UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


Principles  and  Practice 


OF 


AGRICULTURAL  ANALYSIS 


A  Manual   for  the  Study  of  Soils,  Fertilizers,  and 
Agricultural   Products 


For  the  Use  of  Analysts,  Teachers,  and  Students  of  Agricultural 

Chemistry 


SECOND  EDITION,  REVISED  AND  ENLARGED 


VOLUME  II 


FERTILIZERS    AND    INSECTICIDES 


BY  HARVEY  W.  WILEY,  A.M.,  Ph.D. 


EASTON,  PA. 

THE  CHEMICAL  PUBLISHING  CO. 
1908 


53654 


COPYRIGHT,  1908,  BY  HARVEY  W.  WII.KY. 


PREFACE  TO  VOLUME  SECOND 


In  this  volume  an  attempt  has  been  made  to  treat  the  subject  of 
fertilizers  and  fertilizing  materials  in  the  manner  followed  in 
the  first  volume  with  soils.  The  general  principles  of  fertilizer 
manufacture  and  application  have  been  presented  in  so  far  as 
they  seemed  to  throw  light  on  the  rational  method  of  examination 
and  analysis.  The  standard  methods  of  analysis  in  use  in  this 
and  other  countries,  have  been  presented  with  sufficient  fullness 
for  the  guidance  of  the  skilled  worker,  and  the  information  of 
the  student.  To  those  who  make  use  of  a  book  only  for  routine 
work  or  for  preparation  for  an  examination,  this  volume,  as  its 
predecessor,  will  be  found  to  have  little  attraction.  This  fact, 
however,  will  not  be  a  cause  of  regret  to  the  author  whose  pur- 
pose has  been,  avowedly,  to  present  to  the  busy  worker  and  stu- 
dent a  broad  view  of  a  great  subject  which  each  one  does  not  have 
the  time  to  search  out  for  himself. 

It  is  a  matter  of  regret,  however,  that  the  contents  of  the  vol- 
ume have  again  exceeded  all  expectations.  It  was  found  im- 
practicable to  secure  any  greater  condensation  without  depart- 
ing from  the  purpose,  and  impairing  the  completeness  of  the 
work.  When  work  is  done  with  no  prospect  of  financial  com- 
pensation, it  is  gratifying  to  find  it  appreciated,  and  the  author 
will  be  content  to  have  this  volume  meet  with  as  kindly  a  recep- 
tion as  has  been  accorded  volume  one. 

HARVEY  W.  WILEY. 

WASHINGTON,  D.  C., 
End  of  July, 


PREFACE  TO  SECOND  EDITION 


A  great  part  of  the  material  relating  to  the  occurrence  and 
analysis  of  ammonia,  nitrous  and  nitric  acid  printed  in  the  first 
volume  of  the  first  edition  of  this  work  has  been  rewritten  and 
transferred  to  this  volume.  This  rearrangement  has  resulted 
in  making  the  first  and  second  revised  volumes  of  approximately 
the  same  size. 

All  the  matter  of  this  volume  has  been  rewritten  and  brought 
down  to  date.  New  features  of  moment  are  those  relating  to  the 
production  of  nitric  acid  for  manurial  purposes  from  cyanamid 
and  by  direct  electric  oxidation  of  the  nitrogen  of  the  air.  A 
chapter  on  the  analysis  of  insecticides  has  also  been  added. 

While  not  intended  in  any  way  as  a  laboratory  guide  it  is 
hoped  this  volume  may  be  even  more  highly  appreciated  than 
in  its  first  form  by  the  student,  the  investigator  and  the  teacher. 

H.  W.  WILEY. 
November,  190%. 


CONTENTS 


PART  FIRST 

Definitions,  Sampling  and  Preliminary  Treatment,  pp.  1-22. — Waste 
matters  as  fertilizing  materials ;  Waste  materials  as  fertilizers ;  Valuation 
of  fertilizers ;  Trade  valuations  of  fertilizers ;  General  principles  of  sampl- 
ing; Object  of  sampling;  Sampling  a  gas;  Sampling  a  liquid;  Sampling  a 
solid ;  Subdivision  of  sample ;  Sampling  of  fertilizers ;  Mixed  fertilizers ; 
Barn-yard  manures ;  Sampling  of  materials  used  for  road  building ; 
Methods  of  sampling;  Preparation  of  sample  in  laboratory. 

Drying  Samples  of  Fertilisers,  pp.  22-25. — Difficulties  of  desiccation; 
Official  methods ;  General  observations ;  Moisture  in  monocalcium  phos- 
phates. 

Mineral  Phosphates,  pp.  25-40. — Natural  occurrence  of  phosphates ; 
Florida  phosphates ;  Tennessee  phosphates ;  Occurrence  of  black  phos- 
phate ;  Occurrence  of  white  phosphate ;  Origin  of  the  white  phosphates ; 
Utilization  of  white  phosphate. 

Statistics  and  Composition,  pp.  40-49. — Tennessee  phosphates ;  Blue  phos- 
phate ;  South  Carolina  phosphates ;  Magnitude  of  product ;  Production  in 
the  United  States ;  Marketed  production ;  World's  production ;  Quantity 
of  phosphoric  acid  removed  by  crops ;  General  conclusions. 

Analytical  Processes,  pp.  49-121. — Constituents  to  be  determined;  Dis- 
solving phosphates ;  Incineration ;  Loss  of  phosphoric  acid  on  incineration ; 
Official  methods ;  General  methods  for  estimating  phosphoric  acid ;  Prepa- 
ration of  reagents ;  Formula  for  the  reactions ;  Official  method  for  total 
phosphoric  acid;  Influence  of  insoluble  silica;  Use  of  tartaric  acid;  Water- 
soluble  phosphoric  acid ;  Citrate-insoluble  phosphoric  acid ;  Examination  of 
the  pyrophosphate;  Determination  of  available  phosphoric  acid;  Interna- 
tional methods;  Molybdic  acid  method;  French  official  method;  Swedish 
official  method ;  Dutch  official  method ;  Sources  of  error  in  the  molybdate 
method;  Influence  of  aluminum,  magnesium  and  calcium;  Color  of  the 
magnesium  pyrophosphate ;  The  citrate  method ;  German  experiment 
station  method ;  The  Swedish  citrate  method ;  Methods  adopted  by  the 
Brussels  Congress ;  Dutch  citrate  method ;  Method  of  Lasne ;  Compara- 
tive accuracy  of  the  citrate  and  molybdate  methods ;  The  citrate  precipi- 
tate purity ;  The  citrate  method  applied  to  samples  with  small  content 
of  phosphoric  acid ;  Direct  precipitation  of  the  citrate-soluble  phosphoric 
acid ;  Determination  of  phosphoric  acid  with  preliminary  precipitation  as 


Vi  CONTENTS 

stannic  phosphate;  Phosphoric  acid  soluble  in  ammonium  citrate;  Arbi- 
trary determination  .of  reverted  phosphoric  acid;  Theory  of  revision; 
Influence  of  movement;  Digestion  apparatus  for  reverted  phosphates, 
Comparison  of  results ;  Huston's  mechanical  stirrer ;  Precipitation  of 
the  water  and  citrate-soluble  phosphoric  acid;  Veitch's  method  for 
available  phosphoric  acid;  Availability  of  phosphatic  fertilizers. 

Direct  Weighing  of  the  Phosphomolybdate  Precipitate,  pp.  122-130. — 
Method  of  Hanamann;  Method  of  Lorenz;  Method  of  Woy;  Berju's 
modification ;  Method  of  Graftiau ;  Method  of  Pellet ;  Cladding's  modifica- 
tion, 

Volumetric  Determination  of  Phosphoric  Acid,  pp.  130-178. — Classifica- 
tion of  methods ;  Uranium  method ;  Precipitation  of  phosphates  in  pres- 
ence of  citrate ;  Magnesium  citrate  solution ;  Filtration  and  washing ; 
Standard  solution  of  uranium  nitrate ;  typical  solution  of  phosphoric- 
acid  ;  Titration  of  uranium  solution ;  Determination  of  phosphoric  acid 
in  superphosphates ;  Determination  of  soluble  and  reverted  phosphoric  acid ; 
Conclusions ;  Pemberton's  volumetric  method ;  Alkalimetric  estimation  of 
phosphoric  acid;  Comparison  of  weighing  and  titrating  methods;  Esti- 
mation of  phosphoric  acid  as  a  lead  compound ;  Water-soluble  phosphoric- 
acid;  Estimation  of  phosphoric  acid  in  the  presence  of  iron  ;  Methods  of  the 
international  steel  standards  committee ;  Calculating  results ;  The  silver 
method. 

Technical  Determination  of  Phosphoric  Acid,  pp.  179-189. — Desirability 
of  methods ;  Reagents ;  Manipulation ;  Citrate  method ;  Uranium  method  ; 
Determination  of  phosphoric  acid  in  basic  slags ;  Determination  of  phos- 
phoric acid  in  superphosphates ;  Determination  of  free  acid  in  phosphates ; 
Ostersetzer's  method. 

Basic  Phosphatic  Slags,  pp.  190-223. — Uses  of  basic  slag;  History  and 
manufacture ;  Quantity  made ;  Process  of  manufacture ;  Composition 
of  slag  phosphate ;  Molecular  structure ;  Solubility ;  Solvents ;  Method 
of  estimation;  Method  used  at  the  Halle  agricultural  station;  Dutch 
method ;  Estimation  of  citrate-soluble  phosphoric  acid ;  Wagner's  method ; 
Method  of  the  German  agricultural  experiment  stations ;  Preparation 
of  the  citric  acid  extract ;  Direct  precipitation  method ;  German  method 
for  slags  rich  in  silicic  acid ;  Bottcher  method ;  Separation  of  silicic  acid ; 
Estimation  of  total  phosphoric  acid ;  American  methods ;  German  manu- 
facturer's method ;  Estimation  of  lime ;  Detection  of  adulteration. 

Determination  of  Other  Constituents  in  Natural  Phosphates,  pp.  224- 
260. — Water  and  organic  matter ;  Carbon  dioxid ;  Soluble  and  insoluble 
matter ;  Silica  and  insoluble  bodies ;  Loss  of  silica  and  fluorin ;  Esti- 
mation of  lime;  Ammonium  oxalate  method;  Method  of  Immendorff; 
Estimation  of  iron  and  alumina;  The  acetate  method;  Method  of  Hess; 
Method  of  E.  Glaser;  Jones'  variation;  Crispo's  method;  Variation  of 


CONTENTS  Vll 

the  alcohol  method;  Variation  of  Marioni  and  Tasselli;  Method  of  Krug 
and  McElroy;  Method  of  Wyatt;  Separation  of  iron  and  aluminum 
phosphates ;  Methods  of  the  German  fertilizer  association ;  French  meth- 
od; Method  of  Lasne;  Comparison  of  methods  for  iron  and  alumina; 
Sources  of  error;  Effect  of  iron  salts;  Effect  of  calcium  salts;  Effect  of 
sulfates;  Effect  of  fluorin;  Separation  of  alumina  with  phenylhydrazine ; 
General  conclusions. 

Occurrence  of  Fluorin  in  Phosphates,  pp.  261-276. — Significance  of 
fluorin ;  Method  of  Berzelius ;  Chatard's  modification ;  Wyatt's  modifica- 
tion ;  Method  of  Rose ;  Burk's  modification  of  Carnot's  method ;  Method 
of  Lasne ;  Carnot's  modification ;  Protection  of  glassware  from  fluorin ; 
Fluorin  in  bones ;  lodin  in  phosphates ;  Chromium  in  phosphates ;  Vanad- 
ium in  phosphates. 

Superphosphate  Manufacture,  pp.  277-286. — Chemical  changes  in  manu- 
facture ;  Reaction  with  fluorids ;  Reaction  with  carbonates ;  Solution  of 
the  iron  and  alumina  compounds;  Quantity  of  sulfuric  acid;  Use  of 
phosphoric  acid;  Fixation  of  phosphoric  acid;  Absorption  of  phosphoric 
acid;  Availability. 

PART  SECOND 

Nitrogen  in  Fertilisers,  Drainage  Waters,  Hie.,  pp.  287-300. — Kinds  of 
nitrogen  in  fertilizers;  States  of  nitrogen;  Nitrogen  in  seeds  and  seed 
residues;  Nitrogen  in  seaweed;  Dried  blood  and  tankage;  Horn,  hoof, 
and  hair ;  Nitrogen  in  fish ;  Nitrogen  from  birds ;  Waste  nitrogen ;  'Nitro- 
gen in  soils;  Deposits  of  nitrates;  Quantity  of  nitrates  used;  Nitrate 
deposits  in  Chile ;  Nitrate  deposits  in  California ;  Functions  of  sodium 
nitrate;  Composition  of  nitrate  deposits;  Commercial  forms  of  nitrates; 
Composition  of  Chile  saltpeter;  Application  of  saltpeter  to  the  soil. 

Utilization  of  the  Nitrogen  of  the  Air  as  a  Fertilizing  Material,  pp. 
301-320. — Activity  of  leguminous  plants;  Activity  of  other  than  legumin- 
ous plants ;  Accumulation  of  atmospheric  nitrogen  in  the  soil ;  Manufac- 
ture and  use  of  cyanamid ;  Cyanamid  compound  as  a  fertilizer ;  Utiliza- 
tion of  atmospheric  nitrogen ;  Development  of  the  fixation  of  atmos- 
pheric nitrogen;  Properties  of  calcium  cyanamid;  Production  of  nitric 
acid  by  electric  action;  Method  of  Birkeland  and  Eyde;  Manufacture 
of  nitrate  of  lime ;  Quantity  of  nitric  acid  by  electric  action ;  Absorption 
and  concentration  of  product;  Method  of  Moscicki;  Production  of 
nitric  acid  in  the  United  States  by  electric  action. 

Methods  of  Determining  Nitrogen.  Volumetric  Method,  pp.  321-337. — 
Classification  of  methods ;  Determination  of  state  of  combination ; 
Microscopic  examination;  Official  method;  Copper  oxid  method;  Note 
on  copper  oxid  method;  Description  of  apparatus;  Variation  of  Bureau 
of  Chemistry  method  of  Johnson  and  Jenkins;  Calculating  results; 


viii  CONTENTS 

Reading  the  barometer;  Tension  of  aqueous  vapor;  Tables  for  calculat- 
ing results. 

Methods  of  Determining  Nitrogen. — Continued.  Soda-Lime  Process,  pp. 
338-345.— The  official  method;  The  French  method;  The  hydrogen  meth- 
od ;  Coloration  of  the  product ;  General  considerations ;  The  Ruffle  method ; 
Observations;  Boyer's  modification. 

Method  of  Determining  Nitrogen. — Continued.  The  Moist  Combustion 
Process,  pp.  346-372.— Method  of  Kjeldahl;  Theory  of  the  reaction;  Prepar- 
ation of  reagents ;  Modification  of  the  process ;  Method  of  Wilfarth ;  Dutch 
method;  German  method;  The  Official  method  not  applicable  in  the 
presence  of  nitrates;  Apparatus  employed;  The  Gunning  modification; 
Reactions  of  the  Gunning  process. 

Method  of  Determining  Nitrogen. — Continued.  Changes  in  Kjeldahl 
Method  to  Include  Nitric  Acid,  pp.  373-382. — Modifications  of  Asboth ;  Var- 
iation of  Jodlbauer ;  The  Dutch  method ;  The  Halle  method ;  The  salicylic 
acid  method ;  Use  of  zinc  sulfid  and  sodium  thiosulfate ;  Theory  of  the  pro- 
cess; The  official  method;  Gunning  method  for  nitric  acid;  The  official 
Gunning  method. 

Determination  of  Nitrogen  in  Definite  Forms  of  Combination,  pp. 
382-390. — Introductory  considerations ;  Nitrogen  as  ammonia ;  Method 
of  Boussingault ;  Nitrogen  as  thiocyanates ;  Separation  of  proteid  from 
amid  nitrogen ;  Separation  of  nitric  and  ammoniacal  nitrogen ;  French 
method;  German  method;  Perchloric  acid  in  ChUe  saltpeter. 

The  Nitric  Acid  Process,  pp.  391-424. — Occurrence  of  oxidized  nitro- 
gen; Method  of  Schloesing;  Schloesing's  modified  method;  French  agri- 
cultural method ;  Method  of  French  sugar  chemists ;  Method  of  Schloes- 
ing and  Wagner ;  Modification  of  Warington ;  Preparation  of  the  samples ; 
Measurement  of  the  gas;  Spiegel's  modification;  de  Koninck's  modifi- 
cation ;  Schmidt's  process ;  Merits  of  the  ferrous  chlorid  process ;  The 
Crum-Frankland  process;  Warington's  modification;  Wo/s  method; 
Lunge's  nitrometer;  Utility  of  the  method;  Method  of  Gantter;  Analysis 
of  Chile  saltpeter;  Method  of  difference. 

Estimation  of  Nitric  Acid  by  Oxidation  of  a  Colored  Solution.  Indigo 
Method,  pp.  425-432.— Method  of  Marx;  Method  of  Boussingault; 
Method  of  Warington;  Experimental  data;  General  directions. 

Determination  of  Nitric  Acid  by  Reduction  to  Ammonia,  pp.  433-440. — 
Classification  of  methods  ;  Reduction  in  alkaline  solutions ;  Qualitative 
test*  for  nitrates ;  Sodium-amalgam  methods ;  Method  of  the  Mockern 
agricultural  station ;  The  Halle  zinc-iron  method  ;  Method  of  Beck ; 
Method  of  Devarda  ;  Variation  of  Stoklasa  ;  Method  of  Sievert. 

Reduction  in  an  Acid  Solution,  pp.  441-446. — The  sodium-amalgam  pro 
cess;  Method  of  Schmitt;  Method  of  Ulsch ;  Ulsch  method  applied  to 
mixed  fertilizers  ;  Kruger's  method. 


CONTENTS  IX 

Reduction  by  Electric  Current,  pp.  447-449.— Method  of  Williams- 
Warington ;  Nitrogen  in  rain  water ;  Determination  of  ammonia ;  Prep- 
aration of  the  copper-zinc  couple;  Aluminum-mercury  couple. 

lodometric  Estimation  of  Nitric  Acid,  pp.  450-454. — Method  of  de  Kon- 
inck  and  Nihoul;  McGowan's  apparatus;  Method  of  Gooch  and  Gruener. 

Estimation  of  Nitric  Acid  by  Colorimetric  Comparison,  pp.  455-467. — 
Delicacy  of  the  method ;  Hooker's  method ;  Influence  of  other  bodies ; 
Phenylsulfuric  acid  method;  Method  of  Gill;  Variation  of  Johnson; 
Estimation  of  nitric  in  presence  of  nitrous  acid ;  Piccini  process ;  Colors 
produced  by  diphenylamin. 

Estimation  of  Nitrous  Acid,  pp.  467-476. — Metaphenylenediamin  meth- 
od; Sulfanilic  acid  method;  Preparation  of  sulfanilic  acid;  Method  of 
Mason ;  Lunge  and  Lwoff  method ;  Use  of  starch  as  indicator ;  Method 
of  Chabrier;  Ferrous  salt  process. 

Volumetric  Process  for  Nitrous  Acid,  pp.  477-479. — Decomposition 
with  potassium  ferrocyanid;  General  observations. 

Determination  of  Free  and  Albuminoid  Ammonia,  pp.  480-484. — Ness- 
ler  process ;  Nessler  reagent ;  Conduct  of  the  analysis ;  Ilosvay's  modi- 
fication ;  Pure  water. 

PART  THIRD 

Potash  and  Fertilising  Materials  in  Fertilizers,  pp.  485-526. — Intro- 
duction; Occurrence  of  Potash;  Historical  sketch;  Deposits  at  Stassfurt; 
Deposits  in  Alsace ;  Mining  the  salts ;  Concentrating  the  salts ;  Compo- 
sition of  crude  salts ;  Kainit ;  Carnallit ;  Polyhalit ;  Kruget ;  Sylvin ; 
Sylvinit ;  Kieserit ;  Schonit ;  Potassium  sulfate ;  Potassium  magnesium 
carbonate ;  Potash  in  factory  residues ;  Production  of  crude  salts ; 
Production  of  concentrated  potash  salts;  Consumption  of  potash; 
Amount  of  potash  used  in  the  different  states ;  Changes  in  potash  salts ; 
Theory  of  deposition ;  Geological  relations ;  van't  Hoff's  theory ;  Dia- 
grams of  crystallization;  Potash  from  feldspar;  Cushman's  investiga- 
tions ;  Experiments  with  potash  feldspar ;  Effects  of  'ground  feldspar ; 
Extraction  of  potash  from  ground  rocks ;  General  conclusions. 

Organic  Sources  of  Potash,  pp.  526-537. — Tobacco  stems  and  waste; 
Cottonseed  hulls  and  meal ;  Wood  ashes ;  Fertilizing  value  of  wood  ashes ; 
Availability  of  potash  in  ashes ;  Potash  in  beet  molasses ;  Potash  in  win- 
ery residue ;  Insoluble  potash  in  plants ;  Forms  of  potash  in  fertilizers ; 
Quantity  of  potash  removed  by  crops. 

Methods  of  Analysis  of  Potash.  Preparation  of  Sample,  pp.  538-577.— 
Destruction  of  organic  matter  by  ignition ;  Destruction  of  organic  mat- 
ter by  sulfuric  acid ;  Qualitative  detection ;  The  platinic-chlorid  method  ; 
Official  method ;  Optional  method ;  French  method ;  German  method ; 
Dutch  method;  Swedish  method;  Methods  of  the  potash  syndicate; 


X  CONTENTS 

Methods  for  concentrated  salts ;  Methods  for  calcined  salts ;  Prepara- 
tion of  solutions ;  Lunge's  modification  of  technical  methods ;  The  bar- 
ium-oxalate  method ;  Method  of  de  Roode ;  Calcium-chlorid  method ; 
Moore's  method  modified  by  Veitch;  Application  of  the  platinum 
method  in  presence  of  sulfates ;  Rapid  control  method ;  Weighing  the 
precipitate  as  metallic  platinum;  Sources  of  error  in  the  platinum  meth- 
od; Effect  of  concentration;  Differences  in  crystalline  form;  Factors  for 
potash;  Recovery  of  platinum  waste;  Preparation  of  chlor-platinic  acid. 
Estimation  of  Potash  as  Perchlorate,  pp.  578-593. — General  principles; 
Schloesing's  modification ;  Kaspar's  method  for  preparing  perchloric 
acid;  Kreider's  method;  Keeping  properties  of  perchloric  acid;  Tech- 
nique of  the  process ;  Disturbing  factors ;  Removal  of  sulfuric  acid ; 
Application  to  crude  potash  salts ;  Influence  of  carbonates ;  Applicability 
of  the  process;  Accuracy  of  the  process. 

PART  FOURTH 

Miscellaneous  Fertilisers,  pp.  594-625. — Classification ;  Forms  of  lime ; 
Application  of  lime;  Action  of  lime;  Best  forms  of  lime;  Analysis  of 
lime ;  Gypsum ;  Analysis  of  gypsum ;  Solubility  in  sodium  carbonate ; 
Common  salt ;  Green  vitriol ;  Hen  manure ;  Guanos  and  cave  deposits ; 
Total  phosphoric  acid  in  guanos ;  Waste  leather ;  Analysis  of  wood  ashes ; 
Carbon,  sand,  and  silica ;  Phosphates  and  alkaline  earths ;  Method  of 
McElroy ;  Early  official  methods  for  alkalies ;  Official  methods  for  the 
determination  of  inorganic  plant  constituents ;  Sulfur  in  plants ;  Chlorin 
in  plants ;  Stating  results  of  fertilizer  analyses ;  The  elemental  system ; 
The  objections  to  the  elemental  system;  The  advantages  of  the  elemental 
system ;  The  ionic  system ;  General  conclusions. 

Insecticides  and  Fungicides,  pp.  625-653. — Kinds  of  insect  pests ; 
classification  of  insecticides ;  Paris  green ;  Methods  of  analysis ;  Discus- 
sion of  methods  of  analysis ;  Green  arsenoid ;  London  purple ;  Methods 
of  analysis ;  Discussion  of  methods  of  analysis ;  Lead  arsenate ;  Methods 
of  analysis ;  Insecticides  for  external  sucking  insects ;  Soaps ;  Caustic  soda 
and  potash ;  Methods  of  analysis ;  Lime-sulfur-salt  mixture ;  Methods  of 
analysis;  Kerosine  emulsion;  Tobacco  and  tobacco  extract;  Determi- 
nation of  nicotin ;  Potassium  cyanid ;  Carbon  disulfid ;  Insecticides  for 
stored  grains ;  Insecticides  for  animal  parasites ;  Fungicides ;  Formalde- 
hyde ;  Bordeaux  mixture ;  Copper  sulfate ;  Official  methods  of  analysis ; 
Discussion  of  methods  of  analysis ;  Statement  of  Insecticide  analyses ; 
Scheme  for  reporting  results  of  analysis. 


LIST   OF    ILLUSTRATIONS 


Figure     i.     Apparatus  for  crushing  mineral  fertilizers 12 

2.     Plate   grinder    for   minerals 13 

"         3.     Shaking  apparatus   for  superphosphates 92 

"         4.     Shaking  machine   for  ammonium   magnesium   phosphate 96 

"         5.     Rossler    ignition    furnace 97 

Plate,    figure    6.     Huston's    agitating    machine opposite  1 16 

Figure     7.     Huston's    mechanical    stirrer 118 

"         8.     Jones'    reduction   tube 171 

"         9.     Reductor   and   filter    attachment 175 

10.     Permanganate    burette i?5 

"       ii.     Wagner's   digestion    apparatus    for    slags 202 

"       12.     Lasne's     apparatus 268 

Plate,  figure   13.     Wild  duck's  and  eggs  on  Layson  Island opposite  291 

Figure  14.     Mercury    pump    and    azotometer 32^ 

"       15.  Moist  combustion  apparatus  of  the  Halle  agricultural  laboratory....   359 

"       1 6.     Distillation    apparatus   of   the   Halle    agricultural   laboratory 361 

Plate,   figure    1 7.     Hood opposite     367 

Plate,    figure    18.     Distilling   apparatus opposite  367 

Figure  19.     Trap  of  distilling  apparatus 369 

"       20.     Schloesing's  apparatus   for   nitric   acid 393 

"       21.     Schloesing-Wagner     apparatus 398 

22.  Warington's  apparatus   for   nitric   acid 399 

23.  Schulze-Tiemann's  nitric    acid   apparatus 404 

24.  Spiegel's  apparatus  for  nitric  acid 408 

"       25.     DeKonnick's    apparatus 409 

"       26.     End   of  delivery   tube 410 

27.     Schmidt's    apparatus 413 

"       28.     Lunge's     nitrometer 415 

"       29.     Lunge's   improved    apparatus 417 

30.  Lunge's     analytic     apparatus 420 

31.  Gantter's    nitrogen    apparatus 422 

"       32.     Halle  nitric   acid   apparatus 436 

33.     Stoklasa's   nitiic  acid   apparatus 439 

"       34.     Apparatus    of    Monnier    and    Auriol 441 

35.  McGowan's  apparatus  for  the  iodometric  estimation  of  nitric  acid 451 

36.  Apparatus  of  Gooch  and  Gruener 454 

37.  Apparatus     of     Chabrier 475 

"       38.     Schaeffer's  nitrous  acid  method 478 

39.     Water  distilling  apparatus,  Bureau  of  Chemistry 482 

Plate,   figure   40.     Scene  showing  mining  operation opposite  490 

Plate,  figure  41.     Drilling  in  potash  mine  preparatory  to  blasting opposite  490 

Plate,  figure  42.     Scene  during  lunch  hour  in  a  potash  mine opposite  490 

Figure  43.     Geological  relations  of  the  potash  deposits  near  Stassfurt 507 

44.  Diagram  showing  law  of  crystallization  of  potash  salts 511 

45.  Graphic  representation  of  theory  of  crystallization 513 

46.  Graphic  representation  of  the   deposition  of  different  salts 514 

"       47.     Apparatus   for   making  pure   chlorplatinic    acid 576 


EXAMINATION  OF   FERTILIZING  MATERIALS, 
FERTILIZERS,  AND  MANURE 


PART  FIRST 


DEFINITIONS,  SAMPLING  AND  PRELIMINARY  TREATMENT 

1.  Introduction. — The  principal  plant  foods  occurring  in  soils 
are  named  and  the  methods  of  estimating  them  described  in  the 
first  volume.     As  fertilizers  are  classed  those  materials  which 
are  added  to  soils  to  supply  deficiencies  in  plant  foods  or  to  render 
more  available  the  stores  already  present.  There  is  little  difference 
between  the  terms  fertilizer  and  manure.     In  common  language 
the  former  is  applied  to  materials  prepared  for  the  fanner  by 
the  manufacturer  or  mixer,  while  the  latter  is  applied  to  those 
accumulated  about  the  stables  or  made  elsewhere  on  the  farm. 
Thus  it  is  common  to  speak  of  a  barn-yard  or  stall  manure  and  of 
a  commercial  fertilizer.     This  distinction  is  more  nominal  than 
real.     If  a  choice  is  to  be  made  between  terms,  manure  is  pref- 
erable.    The  term  fertilization,  moreover,  is  applied  biologically 
to  the  effective  congress  of  the  male  and  female  elements  of  the 
egg,  and  thus  confusion  may  arise  by  the  application  of  that  term 
to  any  process  of  manuring. 

In  harmony  with  the  common  practice  in  this  country,  however, 
the  words  will  be  used  in  this  volume  in  the  sense  indicated  above. 

One  of  the  objects  of  the  analysis  of  soils  is  to  determine  the 
character  of  the  fertilizer  which  should  be  added  to  a  field  in 
order  to  secure  its  maximum  fertility. 

One  purpose  of  _the  present  manual  is  to  determine  the  fitness 
of  offered  fertilizing  material  to  supply  the  deficiencies  which  may 
be  revealed  by  a  proper  study  of  the  needs  of  the  soil. 

2.  Occurrence  of  Fertilizers  in  Nature. — In   the  succession    of 
geological  epochs  which  has  marked  the  natural  history  of  the 
earth  there  have  been  brought  together  in  deposits  of  greater  or 
less  magnitude  the  stores  of  plant  food  unused  by  growing  crops 


2  AGRICULTURAL   ANALYSIS 

or  which  may  once  have  been  part  of  vegetable  and  animal  organ- 
isms. 

For  a  full  description  of  the  extent  and  origin  of  these  deposits 
the  reader  is  referred  to  works  on  economic  geology.  A  brief 
description  of  them  is  given  further  on  in  connection  with  the 
fertilizing  materials  which  they  furnish.  These  deposits  are  the 
chief  sources  of  the  commercial  fertilizers  of  a  mineral  nature 
which  are  offered  to  the  farmers  of  to-day  and  to  which  the  agri- 
cultural analyst  is  called  upon  to  devote  much  of  his  time  and 
labor.  The  methods  of  determining  the  chemical  composition  and 
agricultural  value  of  these  deposits,  as  practiced  by  the  leading 
chemists  of  this  country  and  Europe,  will  be  fully  set  forth  in  the 
following  pages. 

3.  Waste  Matters  as  Fertilizing  Materials. — In  addition  to  the 
natural  products  just  mentioned,  the  analyst  will  be  called  on  also 
to  deal  with  a  great  variety  of  waste  materials  which,  in  the  last 
few  years,  have  been  saved  from  the  debris  of  factories,  abattoirs 
and  other  sources  and  prepared  for  use  on  the  farm.     Among 
these  waste  matters  may  be  mentioned  bones,  horns,  hoofs,  hair, 
tankage,  dried  blood,  fish  scrap,  oil  cakes,  ashes,  sewage  and  sew- 
age precipitates,  offal  of  all  kinds,  leather  scraps,  and  organic 
debris  in  general. 

It  is  important,  before  beginning  an  analysis,  and  especially  be- 
fore passing  a  final  judgment  on  the  data  obtained,  to  know  the 
origin  of  the  substances  to  be  determined.  As  has  already  been 
pointed  out  in  the  first  volume,  the  process  which  would  be  ac- 
curate with  a  substance  of  a  mineral  origin  might  lead  to  error 
if  applied  to  the  same  element  in  organic  combination.  This  is 
particularly  true  of  phosphorus  and  potash.  A  simple  micro- 
scopic examination  will  usually  enable  the  analyst  to  determine 
the  nature  of  the  sample.  In  this  manner,  in  the  case  of  a  phos- 
phate, it  would  at  once  be  determined  whether  it  is  derived  from 
bone,  mineral,  or  basic  slag.  The  odor,  color  and  general  con- 
sistence will  also  aid  in  the  determination. 

4.  Valuation  of  Fertilizing  Ingredients. — Perhaps  there  are  no 
more  numerous  and  perplexing    questions    propounded    to    the 
analyst  than  those  which  relate  to  the  value  of  fertilizing  materials. 


TRADE   VALUES  OF   FERTILIZING   INGREDIENTS  3 

There  is  none  harder  to  answer.  As  a  rule,  these  questions  are 
asked  by  the  farmer,  and  refer  to  the  money  value  of  the  fertil- 
izers put  on  his  fields.  In  such  cases  the  cost  of  transportation  is 
an  important  factor  in  the  answer.  The  farther  the  farmer  is  re- 
moved from  the  place  of  fertilizer  manufacture  the  greater,  as  a 
rule,  will  be  the  cost.  Whether  the  transportation  is  over  land  or 
by  water  also  plays  an  important  part  in  the  final  cost.  The  dis- 
covery of  new  stores  of  fertilizing  materials  has  also  much  to  do 
with  the  price.  This  fact  is  especially  noticeable  in  this  country, 
where  the  price  of  crude  phosphates  at  the  mines  has  fallen  in  a 
few  years  from  nearly  six  dollars  to  three  dollars  per  ton.1 

This  decrease  has  been  largely  due  to  discoveries  of  vast  beds 
of  phosphatic  deposits  in  Florida,  North  Carolina,  Tennessee  and 
Wyoming.  The  state  of  trade,  magnitude  of  crops  and  the  vigor 
of  commerce  also  affect,  in  a  marked  degree,  the  cost  of  the  raw 
materials  of  commercial  fertilizers. 

Since  1904  there  has  been  some  improvement  in  prices,  as  is 
seen  by  the  data  on  the  following  page. 

5.  Trade  Values  of  Fertilizing  Ingredients  in  Raw  Materials  and 
Chemicals. — As  has  already  been  mentioned,  the  task  of  fixing  a 
money  value  for  fertilizer  ingredients  is  difficult.  In  fact,  it  is  a 
very  general  opinion  that  such  values  should  be  left  to  the  usual 
mandates  of  trade  and  the  function  of  the  analyst  should  cease 
when  he  has  disclosed  the  character  and  amount  of  each  in- 
gredient of  commercial  value.  The  market  price  is  then  regulated 
by  the  ordinary  conditions  of  demand,  supply  and  transportation. 
In  some  cases  the  laws  of  the  State  require  the  construction  of  a 
table  showing  the  money  value  of  each  of  the  component  parts. 
In  such  a  case  the  analyst  is  guided  by  trade  conditions  and  fur- 
ther by  the  character  or  origin  of  the  material  in  question.  Thus 
soluble  phosphoric  acid  is  far  more  valuable  than  the  insoluble 
variety,  and  nitrogen  in  the  form  of  blood  or  saltpeter  than  nitro- 
gen in  horns,  hoofs  or  hair. 

The  values  proposed  for  1907  by  the  Massachusetts  experiment 
htation  are  given  below. - 

1  The  American  Fertilizer,  1905,  22  :  17. 

8  Massachusetts  Experiment  Station,   1907,  Bulletin   119  :  16. 


4  AGRICULTURAL   ANALYSIS 

Cents  per  pound 

Nitrogen  in  ammonia  salts 17.5 

"         "    nitrates 18.5 

Organic  nitrogen  in  dry  and  fine-ground  fish,  meat,  blood,  and 

in  high-grade  mixed  fertilizers 20.5 

"        "     fine-ground  bone  and  tankage 20.5 

"             "         "     coarse  bone  and  tankage 15.0 

Phosphoric  acid  soluble  in  water 5.0 

"            "      soluble  in  ammonium  citrate 4.5 

"      in  fine-ground  fish  bone  and  tankage 4.0 

''      in  coarse  fish  bone  and  tankage 3.0 

in  cottonseed  meal,   castor  pomace,  and  wood 

ashes 4.0 

"     insoluble  (in  water  and  in  neutral  ammonium 

citrate)  in  mixed  fertilizers 2.0 

Potash  as  sulfate,  free  from  chlorids 5.0 

"      as  muriate,  (chlorid) 4.25 

' '      as  carbonate 8.0 

The  above  schedule  of  trade  values  is  adopted  by  Massachu- 
setts, Connecticut,  Rhode  Island,  Maine,  Vermont,  New  York 

and  New  Jersey.     It  is  based  on  the  current  market  prices  in 
ton  lots  of  the  materials. 

The  values  assigned  by  the  Maryland  station  differ  but  slightly 
from  the  above.3 

Cent*  per  pound 
In  mixed  fertilizers: 

For  nitrogen  as  ammonia 20.0 

' '     potash  ( K2O )  free  of  chlorids 6.0 

"         "       (K2O)  as  chlorid  or  in  kainit 5.0 

"     phosphoric  acid  soluble  in  water  and  ammonium  citrate-  •  •  5.0 

' '     insoluble  phosphoric  acid 2.0 

' '  from  rock  phosphate i  .o 

In  dissolved  rock: 

For  phosphoric  acid  soluble  in  water  and  ammonium  citrate. . .  4.5 

In  ground  bone: 

For  nitrogen  as  ammonia  in  fine  bone 16.0 

"      "     medium  bone 15.0 

in  medium  bone 14.0 

' '  coarse  bone 13.0 

phosphoric  acid  in  fine  bone 5.0 

"     "    medium  bone 4.5 

"     "     medium  bone 4.0 

"     "     coarse  bone '. 2.0 

In  tankage  and  ground  fish  : 

For  nitrogen  as  ammonia 15.0 

"     phosphoric  acid 3.0 

5  The  Maryland  Agricultural  College  Quarterly,  1907,  No.  37  :  3. 


DIRECTIONS  5 

The  organic  nitrogen  in  superphosphates,  special  manures  and 
mixed  fertilizers  of  a  high  grade  is  usually  valued  at  the  highest 
figures  laid  down  in  the  trade  values  of  fertilizing  ingredients  in 
raw  materials ;  namely,  eighteen  and  one-half  cents  per  pound,  it 
being  assumed  that  the  organic  nitrogen  is  derived  from  the  best 
sources;  viz.,  animal  matter,  as  meat,  blood,  bones  or  other  equally 
good  forms,  and  not  from  leather,  shoddy,  hair  or  any  low  priced, 
inferior  form  of  vegetable  matter,  unless  the  contrary  is  evident. 
In  such  materials  the  insoluble  phosphoric  acid  is  not  given  any 
value  or  only  a  mere  trifle  per  pound.  These  values  change  as 
the  markets  vary. 

The  scheme  of  valuation  prepared  by  the  Massachusetts  station 
does  not  include  phosphoric  acid  in  basic  slags.  By  many  experi- 
menters the  value  of  the  acid  in  this  combination,  tetracalcium 
phosphate,  is  fully  equal  to  that  in  superphosphates  soluble  in 
water  and  ammonium  citrate.  It  would  perhaps  be  safe  to  assign 
that  value  to  all  the  phosphoric  acid  in  basic  slags  soluble  in  a 
five  per  cent,  citric  acid  solution. 

Untreated  fine-ground  phosphates,  especially  of  the  soft  variety 
so  abundant  in  many  parts  of  Florida,  have  also  a  high  manurial 
value  when  applied  to  soils  of  an  acid  nature  or  rich  in  humus. 
On  other  soils  of  a  sandy  nature,  or  rich  in  calcium  carbonate, 
such  a  fertilizer  would  have  little  value.  The  analyst  in  giving  an 
opinion  respecting  the  commercial  value  of  a  fertilizer  must  be 
guided  not  only  by  the  source  of  the  material,  its  fineness  or 
state  of  decomposition,  and  its  general  physical  qualities,  but  also 
by  the  nature  of  the  crop  which  it  is  to  nourish  and  the  kind  of 
soil  to  which  it  is  to  be  applied. 

GENERAL  PRINCIPLES  OF  SAMPLING 

6.  Directions. — It  is  impracticable  to  give  definite  directions  for 
getting  samples  of  fertilizers  which  will  be  applicable  to  all  kinds 
of  material  and  in  all  circumstances.  If  the  chemist  himself  have 
charge  of  the  sampling  it  will  probably  be  sufficient  to  say  that  it 
should  accurately  represent  the  total  mass  of  material  at  hand. 
Generally  the  samples  which  are  brought  to  the  chemist  have  been 
procured  without  his  advice  or  direction,  and  he  is  simply  called 
upon  to  make  an  analysis  of  them  as  they  are  presented. 


6  AGRICULTURAL   ANALYSIS 

7.  General  Principles  of  Sampling. — The  report  of  the  chairman 
of  the  committee  charged  with  presenting  to  the  Sixth  Interna- 
tional Congress  at  Rome  the  principles  of  sampling  and  sugges- 
tions in  respect  of  the  method  in  which  they  should  be  carried 
out  contains  the  following  directions.4 

The  subject  of  sampling  for  analysis  may  be  very  properly 
divided  into  a  general  and  a  special  part.  I  therefore  shall  dis- 
cuss the  problem  in  this  way :  First,  with  a  brief  statement  of  the 
general  principles  which  should  underlie  sampling,  followed  by 
some  special  observations  on  sampling  in  special  cases. 

8.  Object  of  Sampling'. — The  object  of  securing  a  sample  for 
analysis  is  self-evident ;  namely,  that  the  sample  should  repre- 
sent exactly,  or  as  nearly  as  possible,  the  mean  composition  of  the 
whole  deposit  or  substance  from  which  it  has  been  separated. 
For  this  reason,  much  must  be  left  in  all  cases  to  the  sound 
judgment  of  the  person  in  charge  of  the  sampling.     This  per- 
son, whenever  possible,  should  be  the  analyst  himself,  as  no  one 
can  judge  so  well  as  the  one  who  is  called  upon  to  do  the  analyt- 
ical  work  the  character  of   the   sample   necessary  to   secure   a 
proper  material  on  which  the  analysis  is  to  be  conducted.  There- 
fore, it  is  almost  impossible  to  lay  down  any  general  principles 
which  should  guide  the  expert  in  securing  the  sample  of  his 
material  unless  the  character  of  that  material  be  known. 

9.  Classes  of  Materials. — The  materials  which  are  to  be  oper- 
ated upon  by  the  analyst  are  naturally  divided  into  three  states, 
namely,  gaseous,  liquid  and  solid.     These  bodies  pass  gradually 
from  one  state  to  another,  and  especially  is  this  true  of  those 
passing  from  a  solid  to  a  liquid  condition.     The  transition  from 
the  liquid  to  the  gaseous  form  is  very  sharp  and  well  defined. 

10.  Sampling  a  Gas. — In     general,     in     the     sampling    of     a 
gaseous  material  it  is  only  necessary  that  the  gaseous  contents  of 
the  vessel,  room  or  space  should  be  thoroughly  mixed  in  order 
that  any  given  portion  of  the  gas  may  represent  the  whole  sample. 
This  is  especially  true  if  the  gases  be  of  a  mixed  character  or  of 
different  specific  gravities.     Where,  for  instance,  carbon  dioxid 

4  Wiley,  Methods  of  Sampling  Materials  for  Analysis,  Atti  del  VI  Con- 
gresso  internazionale  di  Chimica  applicata,  1907,  7  :  170. 


SAMPLING   A   LIQUID  7 

is  generated  in  the  lower  part  of  a  room  filled  with  air,  being  a 
heavier  gas  it  would  naturally  accumulate  as  a  heavy  liquid  would 
accumulate  under  a  lighter  one.  A  sample  of  the  gas,  therefore, 
in  a  confined  space  of  this  kind  would  not  be  representative  of  the 
whole  contents  unless  previous  to  the  sampling  the  whole  were 
subjected  to  violent  stirring.  An  ordinary  electric  fan  properly 
placed  in  a  room  will  within  a  short  time  so  thoroughly  mix  its 
gaseous  contents  that  a  sample  may  be  drawn  which  will  repre- 
sent fully  the  character  of  the  whole. 

In  order  that  a  sample  of  the  gas  may  be  unmixed  and  un- 
absorbed,  it  is  well  that  it  should  be  aspirated  into  a  vessel  filled 
with  a  liquid  with  which  the  gas  is  not  miscible.  Mercury,  of 
course,  is  the  best  liquid  for  this  purpose  for  most  gases,  but  on 
account  of  its  great  weight  and  cost  is  unsuitable.  As  a  rule, 
water  will  be  found  entirely  satisfactory  for  the  aspirating  mate- 
rial, especially  if  the  vessel  be  of  considerable  size  so  that  the  total 
volume  of  gas  drawn  in  is  rather  large.  The  small  quantity  of 
gas  which  will  be  absorbed  may  be  practically  neglected. 

A  very  good  sample  of  gas  may  also  be  secured  by  pumping 
gas  from  any  room  or  confined  space  into  a  dry  rubber  bag  which 
is  previously  completely  flattened  out  so  as  to  expel  any  air  which 
it  may  contain.  In  order  that  the  last  traces  of  air  may  be  ex- 
pelled, it  is  advisable  in  a  case  of  this  kind  to  fill  the  rubber  bag 
at  least  partially  full  of  gas,  remove  it  from  the  room  where  the 
sampling  is  made,  and  express  the  contents,  then  carry  back  into 
the  room  and  refill. 

Gases  may  also  be  sampled  into  eudiometers  or  other  vessels  in 
which  the  analytical  processes  are  to  be  carried  out.  In  all  these 
cases  the  study  of  the  nature  of  the  case,  the  experience  of  the 
analyst  and  the  character  of  the  analysis  will  determine  the  meth- 
ods which  are  best  adapted  to  the  purpose. 

ii.  Sampling  a  Liquid. — The  sampling  of  liquid  bodies  is  to  be 
accomplished  in  the  same  general  way.  A  thorough  stirring 
of  the  liquid  should  always  precede  the  sampling  in  order  that 
the  sample  may  be  uniform  in  character.  The  stirring  may 
be  made  either  by  mechanical  means,  as  usually  practiced,  or, 
if  the  liquid  be  one  which  does  not  contain  a  large  amount  of 


8  AGRICULTURAL   ANALYSIS 

gas,  pure  air  may  be  blown  through  it.  The  mechanical  method 
by  paddles  or  other  stirrers,  however,  is  to  be  preferred  when 
it  can  be  practiced.  The  sampling  of  water  for  analytical  pur- 
poses requires  special  methods  which  will  be  given  later. 

12.  Sampling  a  Solid. — The  general  principles  which  should 
underlie  and  regulate  the  sampling  of  solid  materials  are 
more  difficult  to  enunciate.  Here  we  have  the  greatest  variety  of 
conditions.  Solid  materials  may  be  of  such  a  character  that  they 
may  be  easily  mixed ;  as,  for  instance,  in  the  case  of  a  powder  or 
any  substance  in  a  finely  subdivided  state.  On  the  other  hand,  a 
material  from  which  a  sample  is  to  be  taken  may  be  solid,  ex- 
tremely hard  and  difficult  of  disintegration,  as  is  the  case  with  a 
rock  or  a  piece  of  metal  or  of  wood.  The  difficulties  which  ob- 
tain, therefore,  are  very  great  in  this  class  of  bodies  and  require 
special  precautions,  great  experience  and  knowledge  of  the  sub- 
ject and  the  exercise  of  patience  in  order  that  good  results  may  be 
secured.  Where  bodies  can  be  perforated — as  in  the  case  of  wood 
—very  good  samples  may  be  taken  by  means  of  augers  which  are 
made  to  penetrate  the  wood  at  different  places,  and  thus  a  sam- 
ple secured.  If  the  material  is  contained  in  bags  or  barrels 
which  are  easily  penetrated,  the  ordinary  trier  which  is  used  for 
sampling  is,  as  a  rule,  sufficient  to  give  an  average  sample.  In  the 
case  of  metal,  boring  may  be  practiced  with  a  small  drill  and  rea- 
sonably satisfactory  samples  secured. 

The  local  conditions  which  obtain,  the  character,  size  and  shape 
of  the  body,  the  facilities  at  hand  for  sampling,  the  purpose  for 
which  the  analysis  is  to  be  made,  and  the  general  environment  will 
be  sufficient  to  guide  the  expert  analyst  in  his  work  and  enable 
him  to  get  a  sample  of  material  which  to  him  is  a  reasonably  sat- 
isfactory representative.  In  a  little  more  general  way  it  may  be 
said  in  regard  to  liquids  which  are  supposed  to  have  been  mixed 
at  one  time  and  which  have  been  barreled  or  bottled — as  in  the 
case  of  wine,  vinegar  or  beer — it  is  always  advisable  to  take  a 
portion  of  the  sample  from  each  package.  Solids  which  are  finely 
divided  and  evenly  mixed  according  to  a  uniform  standard  and 
which  have  been  taken  from  a  single  source,  as,  for  instance,  in 
the  case  of  fertilizers  which  are  contained  in  bags,  should  have  at 


SUBDIVISION    OF    SAMPLE  9 

least  a  sample  taken  from  every  tenth  bag.  If  there  are  less 
than  ten  bags,  however,  not  less  than  three  or  four  of  the  bags 
should  be  sampled. 

In  regard  to  the  preservation  of  samples  after  they  are  secured, 
ordinary  fruit  jars  which  are  furnished  with  rubber  gaskets  may 
be  used  for  liquids  without  any  fear  of  loss.  In  the  case  of  liquids, 
where  a  narrow-necked  receptacle  is  employed,  and  especially 
where  it  is  necessary  or  advisable  to  secure  a  small  volume  of 
sample,  a  bottle  which  is  closed  with  a  rubber  stopper  may  be 
used.  A  cork  stopper  which  has  been  coated  with  paraffin  and 
afterwards  secured  with  sealing  wax  may  be  substituted  some- 
times to  advantage  for  a  rubber  stopper.  Of  course,  in  many 
cases  the  presence  of  paraffin  is  objectionable,  and  in  such  cases 
it  should  not  be  used. 

13.  Subdivision  of  Sample. — The  extent  of  the  subdivision 
of  the  sample  depends  entirely  on  its  nature  and  the 
character  of  the  examinations  to  be'  made.  In  general 
it  may  be  said  that  the  finer  the  subdivision  the  better 
the  analytical  results.  When  substances  are  dry  and  can  be  easily 
pulverized,  they  should  be  powdered  and  passed  through  a  sieve 
with  a  millimeter  or,  better  still,  a  half  millimeter  mesh.  The 
sample  may  be  selected  advantageously  from  a  large  amount  of 
material  by  repeated  quartering,  the  subsamples  being  passed  suc- 
cessively through  the  crusher  from  time  to  time  so  as  to  have  only 
a  small  amount  of  the  sample  in  a  fine  state  of  subdivision  when 
the  final  grinding  occurs.  In  the  case  of  a  tough  and  difficultly 
reduced  substance  like  meat,  as  large  a  quantity  as  possible  should 
be  passed  repeatedly  through  a  sausage  mill,  mixing  the  whole 
at  once  for  each  grinding,  quartering  the  residue  and  regrinding, 
and  mixing  the  subsamples. 

Many  products  which  consist  of  relatively  small  particles  which 
can  not  be  ground  may  be  thoroughly  mixed  together  and  sub- 
divided by  means  of  quartering  until  a  sample  of  proper  size  is 
obtained.  If  this  material  is  soluble  in  water,  the  whole  of  the 
sample  may  be  weighed,  dissolved  in  water  and  an  aliquot  por- 
tion of  the  mixture  taken  for  analysis.  If  soluble  in  other  solvents 
than  water,  a  similar  process  is  to  be  employed.  It  appears  that 


10  AGRICULTURAL   ANALYSIS 

the  complete  mixture  of  many  substances  which  are  soluble  and 
which  are  of  such  a  nature  that  they  can  not  be  readily  ground  is 
best  effected  by  dissolving  them  in  water  or  some  other  satisfac- 
tory solvent,  mixing  the  solution  and  taking  an  aliquot  part  there- 
of, as  above  suggested. 

If  liquids  have  solids  in  suspension  it  is  often  necessary  to  thor- 
oughly mix  them  in  order  that  the  sample  may  contain  its  pro- 
portionate part  of  the  solid  matters.  Milk  may  be  sufficiently 
mixed  by  pouring  several  times  from  one  receptacle  to  another 
before  the  sample  is  removed.  Carbonated  liquids  may  be  with- 
drawn from  the  casks  or  bottles  in  which  they  are  held  by  means 
of  a  spiggot  with  a  stop-cock.  In  the  case  of  viscous  substances 
a  large  spatula,  cheese-knife  or  cheese-sampler  may  be  con- 
veniently employed.  For  instance,  this  method  of  sampling  may 
be  practised  with  a  substance  like  massecuite.  In  case  the  degree 
of  fluidity  is  too  great  to  admit  of  such  a  method  of  sampling,  a 
slotted  tube  may  be  use'd  which  is  inserted  in  the  semi-liquid  mass 
until  filled  and  then  withdrawn  and  its  contents  removed  for  the 
sample.  Sirups  and  molasses  in  which  the  sugar  has  been  par- 
tially crystallized  offer  unusual  difficulties  in  sampling,  owing  to 
the  great  difficulty  of  breaking  up  the  crystals  and  mixing  them 
uniformly  with  the  liquid  portions.  In  such  cases  it  is  better  to 
dissolve  the  crystals  if  possible  by  gentle  heating  and  stirring  of 
the  products,  or  even  the  addition  of  a  known  amount  of  water 
until  the  whole  of  the  crystallized  portions  are  dissolved. 

There  are  some  plastic  materials  which  it  is  almost  impossible 
to  sample  in  a  uniform  way.  In  these  cases  it  may  be  found  neces- 
sary to  subdivide  the  material  by  cutting  a  selected  and  occasional 
piece  representing,  as  nearly  as  possible,  the  whole  material. 
Materials  like  street  sweepings  and  garbage  may  be  sampled 
when  they  are  loaded  or  unloaded  by  taking  an  occasional  shovel- 
ful and  throwing  it  off  to  itself,  until  a  carload  or  other  large 
quantity  has  thus  been  sampled.  These  materials  which  are  re- 
moved may  then  be  thoroughly  mixed  together  and  resampled  in 
the  same  way. 

Sugar-cane  and  sugar-beets  may  be  sampled  by  taking  at  ran- 
dom every  tenth  or  hundredth  beet  or  cane.  The  same  is  true 


SAMPLING   OF   FERTILIZERS  II 

of  apples  and  other  fruits.  In  such  sampling1  care  must  be  exer- 
cised not  to  select  the  particular  individual  to  be  sampled,  but  to 
take  every  one  which  comes  within  the  prescribed  limit.  In 
general,  it  may  be  said  that  it  would  be  advisable  to  divide  the 
materials  which  are  the  usual  subjects  of  analysis  into  different 
classes  and  subdivisions,  and  that  uniform  methods  for  these 
classes  and  subdivisions  be  recommended. 

14.  Sampling  of  Fertilizers. — Perhaps  there  are  no  more  numer- 
ous and  perplexing  questions  connected  with  the  subject  of 
sampling  than  those  which  arise  in  the  case  of  fertilizers.  In 
many  countries  the  method  of  sampling  the  fertilizing  materials 
i;;  prescribed  by  law.  It  is  impracticable  to  give  definite  direc- 
tions in  all  cases  which  will  be  applicable  to  all  kinds  of  materials 
and  in  all  instances.  The  chemist  himself  having  charge  of  secur- 
ing the  sample  should  see  that  it  accurately  represents  the  total 
amount  of  the  material  sampled.  Too  often  the  samples  which 
are  brought  to  the  chemist  have  been  secured  without  his  advice  or 
direction  and  really  are  not  representative. 

For  sampling  manufactured  fertilizers,  which  in  this  country 
are  usually  very  finely  divided,  I  have  found  nothing  better  than 
a  slotted  brass  tube.  The  tube  may  be  from  I  to  il/2  inches  in 
diameter,  with  a  half  or  three-quarter  inch  slot.  It  should  be 
long  enough  to  reach  the  full  length  of  the  package,  and  the  lower 
end  should  be  provided  with  a  cutting  edge  that  it  may  be  forced 
into  the  package  easily.  For  a  handle  a  smaller  tube  3  to  4  inches 
long  is  brazed  at  right  angles  to  the  upper  end  of  the  larger  tube. 
In  sampling,  the  package  of  fertilizer  is  thrown  on  the  side,  and 
if  the  contents  are  hard  they  are  broken  up  by  rolling  and  by 
blows  on  the  container.  The  slotted  tube  is  now  forced  into  the 
package  with  the  slot  down,  turned  over,  shaken  slightly  to  fill 
the  tube,  withdrawn,  and  the  content  emptied  on  a  rubber  or  oil 
cloth.  Samples  are  drawn  from  at  least  five  per  cent,  of  the  pack- 
ages, but  should  always  be  drawn  from  at  least  three  packages. 
These  samples  are  thoroughly  mixed  on  the  oloth,  a  subsample 
secured  by  quartering,  placed  in  a  screw-top  can  and  labeled 
for  identification.  This  instrument  and  method  are  suitable  for 
sampling  all  finely  ground  fertilizers  and  fertilizer  materials,  but 


12 


AGRICULTURAL   ANALYSIS 


are  hot  suitable  for  raw  phosphate  rock,  coarse  raw  tankage,  fish 
scrap,  farm  manures,  tobacco  stems,  unground  kainit,  nor  for 
very  lumpy  nitrate  of  soda  and  sulfate  of  ammonia,  all  of  which, 
except  when  mechanical  devices  are  used,  leave  much  to  the  judg- 
ment of  the  sampler,  and  for  which  only  general  instructions  can 
be  given. 

Large  samples  should  be  secured  from  five  to  ten  per  cent,  of 
the  material,  being  careful  to  maintain  the  proper  relation  between 
the  coarse  and  fine  portions,  and  to  protect  the  sample  from  loss 
or  absorption  of  moisture.  When  the  material  is  very  wet,  as  fish 
scrap,  or  may  take  up  much  moisture,  as  sulfate  of  ammonia, 
the  sample  should  be  weighed  and  brought  into  an  air-dry  condi- 
tion, and  again  weighed.  It  is  now  coarsely  ground,  thoroughly 


Kig.  i.    Apparatus  for  Crushing  Mineral  Fertilizers. 

mixed  and  a  subsample  taken,  which  may  be  again  ground  and 
subsampled  if  necessary.  The  loss  or  gain  in  bringing  to  an  air- 
dry  condition  must  be  carefully  noted  and  the  results  of  the 
analysis  corrected  thereby. 

15.  Minerals  Containing  Fertilizing  Materials. — When  possible, 
the  samples  should  be  accompanied  by  a  description  of  the  mines 
where  they  are  procured  and  a  statement  of  the  geologic  condi- 


MIXED    FERTILIZERS  13 

tions  in  which  the  deposits  were  made.  As  large  a  quantity  of  the 
material  as  can  be  conveniently  obtained  and  transported  should 
be  secured.  Where  a  large  quantity  of  mineral  matter  is  at  hand 
it  should  first  be  put  through  a  crusher.  Many  forms  of  'crusher, 
driven  by  hand  and  other  power,  are  on  the  market.  They  are  all 
constructed  essentially -on  the  same  principle,  the  pieces  of  mineral 
being  broken  into  small  fragments  between  two  heavy  vibrating 
steel  plates.  The  general  form  of  these  crushers  is  seen  in  Fig.  i. 

The  fragments  coming  from  the  crusher  can  be  reduced  to  a 
coarse  powder  by  means  of  the  iron  plate  and  crusher  shown  in 
Fig.  2. 

Where  only  a  small  quantity  of  mineral  is  at  hand  the  appa- 
ratus just  mentioned  may  be  used  at  once  after  breaking  the 
sample  into  small  fragments  by  means  of  a  hammer. 

Finally  the  sample,  if  to  be  dissolved  in  an  acid  for  sol- 
uble materials  only,  is  reduced  to  a  powder  in  an  iron  mortar 
until  it  will  pass  a  sieve  with  a  one,  or,  better,  one-half  millimeter 


Fig.  2.     Plate  Grinder  for  Minerals. 

circular  mesh.  The  powder  thus  obtained  must  be  stirred  with 
a  magnet  to  remove  all  iron  particles  that  may  have  been  incor- 
porated with  the  mass  by  abrasion  of  the  instruments  employed. 

If  a  complete  mineral  analysis  of  the  sample  is  to  be  secured, 
the  material  freed  from  iron,  as  above  described,  is  to  be  rubbed 
to  an  impalpable  powder  in  an  agate  mortar. 

16.  Mixed  Fertilizers. — In  securing  a  sample  of  mixed  fertiliz- 
ers the  first  requisite  is  that  they  should  be  homogeneous.  If  a  part 
of  one  kind  of  a  fertilizer  be  in  excess  in  any  part  of  the  whole, 


14  AGRICULTURAL   ANALYSIS 

the  sample  is  apt  to  be  nonrepresentative.  The  finer  the  materials 
in  the  original  state  and  the  more  thoroughly  they  have  been 
mixed  the  better  the  sample  will  be.  If  the  materials  be  in  bags 
it  will  b*e  sufficient  to  take  portions  from  every  tenth  bag  or  from 
three  or  four  of  the  bags  if  there  be  less  than  ten,  by  means  of  an 
ordinary  trier  which  is  thrust  through  the  bag  and  filled  with  the 
material  therein  contained.  This  consists  of  a  long  metal  im- 
plement such  as  would  be  formed  by  a  longitudinal  section  of  a 
tube.  The  end  is  pointed  and  suited  for  penetrating  into  the 
sack  and  the  materials  contained  therein.  On  withdrawing  it, 
the  semi-circular  concavity  is  found  filled  with  the  material 
sampled.  Samples  in  this  way  are  removed  from  various  parts 
of  the  bag  and  these  samples  well  mixed  together  and  a  sub- 
sample  of  the  amount  necessary  for  the  laboratory  is  then  ob- 
tained. Quite  a  great  deal  more  of  the  sample  should  be  secured 
than  is  necessary  for  the  analysis  and  this  quantity  may  be 
called  the  "Industrial  Sample."  When  the  industrial  sample, 
more  or  less  voluminous,  reaches  the  laboratory,  the  chemist  is  to 
begin  by  taking  a  note  of  the  marks,  labels  and  descriptions  found 
thereon,  and  of  the  nature  and  state  of  the  package  which  con- 
tains it  and  the  date  of  its  arrival.  All  this  information  should 
be  entered  upon  the  laboratory  book  and  afterwards  transcribed 
on  the  paper  containing  the  results  of  the  analysis,  as  well  as  the 
name  of  the  person  sending  it.  This  having  been  done,  the  sam- 
ple is  to  be  properly  prepared  in  order  that  a  portion  may  be 
taken  representing  the  mean  composition  of  the  whole. 

If  it  is  in  a  state  of  fine  powder,  such  as  ground  phosphates 
and  certain  other  fertilizers,  it  is  sufficient  to  pass  it  two  or  three 
times  through  a  sieve  with  meshes  one  millimeter  in  diameter, 
taking  care  to  break  up  the  material  each  time  in  order  to  mix 
it  and  to  pulverize  the  fragments  which  the  sieve  retains.  The 
whole  is  afterwards  spread  in  a  thin  layer  upon  a  large  sheet 
of  paper  and  a  portion  is  taken  here  and  there  upon  the  point  of 
a  knife  until  about  twenty  grams  are  removed,  and  from  this 
the  portion  subjected  to  analysis  is  afterwards  taken. 

If  the  sample  comes  in  fragments,  more  or  less  voluminous, 
such  as  phosphatic  rocks  or  coarsely  pulverized  guanos  contain- 


MIXED    FERTILIZERS  15 

ing  agglomerated  particles,  it  is  necessary  first  to  reduce  the 
whole  to  powder  by  rubbing  it  in  a  mortar  or  by  using  a  small 
drug  mill.  It  is  next  passed  through  a  sieve  of  the  size  men- 
tioned above  and  that  which  remains  upon  the  sieve  pulverized 
anew  until  all  has  passed  through.  This  precaution  is  very  im- 
portant, since  the  parts  which  resist  the  action  of  the  pestle  most 
have  often  a  composition  different  from  those  which  are  easily 
broken. 

When  the  products  to  be  analyzed  contain  organic  materials, 
such  as  horn,  flesh,  dry  blood,  etc.,  the  pulverization  is  often  a 
long  and  difficult  process,  and  results  in  a  certain  degree  of  heat- 
ing, which  drives  off  some  of  the  moisture  in  such  a  way  that  the 
pulverized  product  is  at  the  last  drier,  and,  consequently,  richer 
than  the  primitive  sample.  It  is  important  to  take  account  of  this 
desiccation,  and  since  the  pulverization  of  a  mass  so  voluminous 
can  not  be  made  without  loss,  the  determination  of  the  total  weight 
of  the  sample  before  and  after  pulverization  does  not  give  exact 
results.  In  such  a  case  it  is  indispensable  to  determine  the  mois- 
ture both  before  and  after  pulverizing,  and  to  calculate  the  analyt- 
ical results  obtained  upon  the  pulverized  sample  back  to  the  orig- 
inal sample.  In  order  to  escape  this  necessity,  as  well  as  the  diffi- 
culties resulting  from  the  variations  in  moisture  during  transpor- 
tation, some  chemists  have  thought  it  better  to  always  dry  the 
commercial  products  before  submitting  them  to  analysis,  and  to 
report  their  results  in  the  dry  state,  accompanied  by  a  determina- 
tion of  the  moisture,  leaving  thus  to  the  one  interested  the  labor 
of  calculating  the  richness  in  the  normal  state,  that  is  to  say,  in 
the  real  state  in  which  the  merchandise  was  delivered. 

In  addition  to  the  fact  that  this  method  allows  numerous 
chances  of  errors,  many  substances  undergoing  important  changes 
in  their  composition  by  drying  alone,  it  has  been  productive  of 
the  most  serious  consequences.  The  sellers  have  placed  their 
wares  on  the  market  with  the  analysis  of  the  material  in  a  dry 
state,  and  a  great  number  of  purchasers  have  not  perceived  the 
fraud  concealed  under  this  expression  so  innocent  in  appearance. 
It  is  thus  that  there  has  been  met  with  in  the  markets  guano  con- 
taining twenty-five  per  cent,  of  water,  which  was  guaranteed  to 


16  AGRICULTURAL   ANALYSIS 

contain  twelve  per  cent,  of  phosphoric  acid,  when  in  reality  it  con- 
tained only  eight  per  cent,  in  the  moist  state. 

17.  Barn- Yard  Manures. — The  sampling  of  stall  and  barn-yard 
manures  is  more  difficult  on  account  of  the  fact  that  the  materials 
are  not  homogeneous  and  that  they  are  usually  mixed  with  straw 
and  other  debris  from  the  feed  trough,  and  only  the  greatest  care 
and  patience  will  enable  the  operator  to  secure  a  fair  sample. 

In  the  case  of  liquid  manures  the  liquid  should  be  thoroughly 
stirred  before  the  sample  is  taken.  In  a  given  case  the  difficulty 
of  securing  representative  samples  of  stall  manure  is  described 
and  also  methods  of  removing  it.6  The  stall  manure  sampled  had 
been  piled  in  the  cattle-yard  for  a  time  and  the  cattle  were  al- 
lowed to  run  over  the  heaps  for  an  hour  or  two  each  day.  Pigs 
.were  allowed  free  access  to  the  heaps  in  order  to  insure  a  more 
perfect  mixture  of  the  ingredients. 

Twenty-nine  loads  of  3000  pounds  each  were  sampled  from  the 
exposed  heap  and  34  loads  of  2000  pounds  each  were  sampled 
from  the  covered  heap.  From  each  load  were  removed 
two  carefully  selected  portions  of  10  pounds  each,  which 
were  placed  in  separate  covered  boxes  numbered  A  and  B.  When 
the  sampling  was  completed  these  boxes  were  covered.  After 
being  removed  to  the  laboratory  the  boxes  were  weighed  and  the 
contents  thoroughly  mixed.  Two  samples  of  12  liters  each 
were  drawn  from  each  box.  One-third  of  this  was  chopped  in 
a  large  meat  chopper  and  the  other  two-thirds  taken  into  the 
laboratory  without  being  cut.  These  samples,  on  entering  the 
laboratory,  were  weighed  and  dried  at  a  temperature  of  60°  to 
secure  the  samples  for  analysis. 

18.  Sampling  of  Materials  Used  for  Road  Building. — The  mate- 
rials of  which  roads  are  built,  especially  the  rock  materials,  have 
of  late  years  been  subjected  to  careful  scientific  examination. 
The  methods  may  be  applied  also  to  minerals  containing  fertilizer 
ingredients.     In  the  examination   of  rocks   and   rock  materials 
which  are  used  to  build  roads,  the  sample  which  is  sent  should 
be  large  enough  to  give  assurance  that  it  practically  represents 
the  materials  employed.  For  this  purpose  not  less  than  30  pounds 

5  Proceedings  iath  and  i3th  Meetings  of  the  Society  for  the  Promotion 
of  Agricultural  Science,  1891-2  :  139. 


METHOD    OF    FRENCH    SUGAR    CHEMISTS  1 7 

of  the  sample  should  be  secured.  If  there  seems  to  be  any  reason- 
able doubt  regarding  the  character  of  the  sample,  its  source 
should  be  investigated  and  a  proper  sample  secured.  In  general, 
the  principles  which  should  guide  the  securing  of  samples  of 
this  kind  of  material  are  those  which  are  in  vogue  for  ordinary 
mineral  analyses,  save  the  larger  quantity  of  road  material  which 
is  usually  required. 

19.  Absence  of  Official  Methods. — Although  the  proper  study  of 
a  fertilizer  has  its  chief  economic  value  when  the  analysis  is  con- 
ducted on  a  representative  sample,  the  official  chemists  have  given 
but  scant  attention  to  the  subject  of  sampling.    It  is  evident  that 
a  detailed  description  of  the  procedure  to  be  followed  in  each 
case  would  be  practically  impossible.     In  such  a  variety  of  com- 
pounds as  is  presented  by  fertilizing  materials  and  fertilizers,  and 
especially  manures,  the  good  judgment  of  the  chemist  in  charge  of 
the  sample  must  point  the  way  to  securing  reasonably  satisfactory 
results.     Patience  and  ingenuity  will  lead  to  the  solution  of  the 
most  intricate  problems  which  may  arise. 

20.  Method  of  the  French  Experiment  Stations. — In  the  method 
employed  by  the  French  experiment  stations,  it  is  directed  that 
in  no  case  should  stones  or  other  foreign  particles  be  removed  from 
the   fertilizer  sampled,  but  they  should   enter  into  the   sample 
in,  as  nearly  as  possible,  the  same  proportions  as  they  exist  in 
the  whole  mass. 

In  the  case  of  stones  or  other  solid  masses  which  are  to  be 
sampled,  as  many  portions  as  possible  should  be  taken  from  all 
parts  of  the  heap  and  these  should  be  reduced  to  a  coarse  powder, 
thoroughly  mixed  together  and  sampled. 

In  case  the  material  is  in  the  form  of  a  paste,  if  it  is  homo- 
geneous, it  will  be  sufficient  to  mix  it  well ;  but  in  case  there  is  a 
tendency  for  the  pasty  mass  to  separate  into  two  parts,  of  which 
the  one  is  a  liquid  and  the  other  more  of  a  solid  consistence, 
it  may  be  well  to  get  samples  from  each  in  case  they  can  not  be 
thoroughly  incorporated  by  stirring. 

21.  Method  of  the  French  Association  of  Sugar  Chemists. — The 
method  adopted  by  the  French  sugar  chemists  directs  that  the 
sampling  should  begin  with  the  fertilizer  in  bulk  or  from  a  portion 


18  AGRICULTURAL   ANALYSIS 

used  for  industrial  purposes.  The  part  for  analysis  is  to  be  taken 
from  the  above  sample  after  it  has  been  sent  to  the  laboratory. 
The  method  of  procedure  should  be  varied  according  to  the  con- 
dition of  the  substances  to  be  analyzed. 

The  large  sample  selected  from  the  goods  delivered  to  com- 
merce having  been  delivered  at  the  laboratory,  the  analytical 
sample  is  obtained  as  described  in  16. 

22.  Method  of  the  International  Congress  of  Applied  Chemistry. 
—The  committee  designated  by  the  Fifth  International  Congress 
of  Applied  Chemistry  has  formulated  the  following  general 
principles  of  sampling  fertilizers  and  component  materials  there- 
of.8 

1.  Samples  not  drawn  in  accordance  with  these  regulations  are 
to  be  refused  by  official  analysts,  such  refusal  being  recorded  on 
the  certificate. 

2.  Samples  are  only  to  be  considered  as  properly  identified,  if 
drawn  during  unloading  on  railway  or  quay,  in  the  presence  of 
representatives  of  both  parties,  or  by  a  sworn  sampler,  and  in  ac- 
cordance with  these  regulations. 

3.  In  the  case  of  manufactured  products,  a  sample  is  to  be 
secured  by  means  of  a  sampling  iron  from  every  tenth  bag,  or  if 
the  material  is  in  bulk,  from  at  least  ten  different  places  through- 
out the  parcel. 

4.  In  the  case  of  shiploads  of  raw  materials  every  fiftieth  bag  or 
bucketful  during  discharge   (corresponding  to  two  per  cent,  ot 
the  whole)  is  to  be  set  aside,  and  from  this,  after  first  crushing  to 
at  least  the  size  of  a  hazel-nut,  a  sample  is  to  be  removed  for  the 
determination  of  moisture ;  a  further  sample  for  the  determination 
of  the  constituents  of  value  is  to  be  obtained  in  the  same  way  as  in 
the  case  of  manufactured  products  after  the  sample  has  been  re- 
duced to  a  fine  state  by  grinding  and  sifting. 

5.  The  samples — in  weight  about  300  grams — are   to  be  filled 
loosely  into  strong,  clean  and  absolutely  dry  glass  bottles. 

6.  At  least  three  samples  are  to  be  prepared.  The  bottles  are  to 
be  hermetically  closed  and  sealed  by  the  persons  conducting  the 
sampling. 

6  Fiinfter,   Internationaler  Kongress  fur  angewandte  Chemie,   Bericht, 
1904,  4  : 937. 


PREPARATION  OF  SAMPLE  IN  LABORATORY         1 9 

7.  The  labels  are  to  be  signed  by  the  persons  supervising  the 
sampling  and  are  to  be  attached  by  means  of  the  wax  used  in 
sealing  the  bottles. 

8.  The  samples  are  to  be  kept  in  a  cool,  dark  and  dry  place. 

9.  Materials  of  heterogeneous  composition  must  be  sufficiently 
reduced  in  size  and  mixed  before  bottling. 

23.  Influence  of  State  of  Subdivision. — The  importance  of  good 
sampling  in  securing  reliable  analytical  data  is  shown  by  Riviere 
by  comparing  the  results  of  analysis  of  samples  from  different 
parts  of  the  same  bulk  material.7     The  substance  examined  was 
dried     blood.       A     sample     received     from     a     farmer     was 
passed    as    customary    through    a    mill    and    contained    9.95 
per    cent,    of    nitrogen.     This     being    lower    than     the    guar- 
anty,   led    to    asking    for    a    new    sample    of    not  less  than 
500  grams.  In  this  sample  there  were  found  11.20  per  cent,  of  ni- 
trogen. The  sample  was  then  divided  into  two  portions  by  means 
of  a  sieve.  The  fine  part,  204  grams,  contained  9.40  per  cent,  of 
nitrogen  and  the  coarse  part  12.10  per  cent.  The  two  portions  were 
again  mixed  and  a  sample  analyzed  contained  11.14  per  cent,  of 
nitrogen.   It  is  evident  from  the  above  data  that  in  transportation 
the  fine  particles  tend  to  go  to  the  bottom  and  the  large  to  be  col- 
lected on  the  top  of  the  mass  so  that  even  were  it  well  mixed  at 
the  start,  at  the  end  of  the  journey  samples  from  different  parts 
would  show  varying  contents  of  nitrogen. 

24.  Preparation  of  Sample  in  Laboratory. — The     method     of 
preparing  mineral  fertilizers  for  analysis  has  been  given  under 
the  directions  for  sampling.     Many  difficulties  attend  the  proper 
preparation  of  other  samples,  and  the  best  approved  methods  of 
procedure  are  given  below. 

According  to  the  directions  given  by  the  Association  of  Offi- 
cial Agricultural  Chemists  the  sample  should  be  well  intermixed, 
finely  ground,  and  passed  through  a  sieve  having  circular  per- 
forations one  millimeter  in  diameter.8  The  processes  of  grind- 
ing and  sifting  should  take  place  as  rapidly  as  possible  so  that 
there  may  be  no  gain  or  loss  of  moisture  during  the  operation. 

1  L'Engrais,  1905,  20  :  233. 

•  Division  of  Chemistry,  Bulletin  46,  Revised,  1899  :  n. 


20  AGRICULTURAL   ANALYSIS 

25.  Method   of   the   International   Commission. — The   methods 
adopted  by  the  international  commission  are  as  follows : 

(a)  Dry  samples  of  phosphates  or  other  artificial  manures  may 
be  simply  sifted  and  then  mixed. 

(b)  In  the  case  of  damp  materials,  where  the  above  procedure 
is  not  possible,  the  preparation  must  be  confined  to  a  careful  mix- 
ing by  hand. 

(c)  In  the  case  of  raw  phosphates  and  animal  charcoal,  a  water 
determination  is  to  be  made,  as  confirmatory  evidence. 

(d)  In  dealing  with  substances  which  are  apt  to  lose  water 
during  grinding,  the  moisture  is  to  be  determined  both  before  and 
after  the  preparation  of  the  sample,  the  results  of  the  analysis 
being  afterwards  calculated  back  into  the  original  hygroscopic 
condition  of  the  sample  as  received. 

26.  Method  of  the  French  Agricultural  Stations. — The  man 
ner  of  proceeding  recommended  by  the  French  stations  varies 
with  the  fertilizer.0     If  it  is    not    already    in    the    form    of    a 
powder  it  is  necessary  to  pulverize  it  as  finely  as  possible  by  rub- 
bing it  up  in  a  mortar.     In  certain  cases,  as  with  superphos- 
phates, the  material  should  be  passed  through  a  sieve  having 
apertures  of  one  millimeter  diameter,  all  the  larger  parts  being 
pulverized  until  they  will  pass  this  sieve. 

When  the  matters  are  too  pasty  to  be  divided  in  the  mortar 
they  should  be  divided  by  means  of  a  knife  or  a  spatula.  They 
should  then  be  incorporated  with  a  known  weight  of  inert,  pul- 
verulent matter  such  as  fine  sand,  with  which  they  should  be 
thoroughly  mixed  and  in  subsequent  calculations  the  quantity 
of  sand  or  other  inert  matter  added  must  be  taken  into  consid- 
eration. Usually  a  pasty  state  of  a  fertilizer  is  due  to  the 
humidity  of  the  mixture.  In  this  case  a  considerable  volume  of 
the  sample  is  dried  and  then  reduced  to  a  pulverulent  state. 
In  the  subsequent  calculations,  however,  the  percentage  of  mois- 
ture lost  must  be  taken  into  consideration. 

Before  drying  a  sample  it  is  necessary  to  take  into  considera- 
tion whether  or  not  the  product  will  be  modified  by  desiccation 

9  Grandeau,  Trait£  d'  Analyse  Matieresdes  agricoles,  3rd  Edition,  1897, 
1  =409. 


GERMAN    METHOD  21 

as  would  be  the  case,  for  instance,  with  superphosphates.  With 
these,  which  are  often  in  a  state  more  or  less  agglomerated,  it  is 
recommended  to  introduce,  in  order  to  divide  them,  a  certain 
quantity  of  calcium  sulfate  to  reduce  them  to  a  pulverulent  state. 

In  the  case  of  animal  debris  they  should  be  divided  as  finely 
as  possible  with  the  aid  of  scissors  and  then  passed  through  a 
drug  mill  if  dry  enough.  They  are  then  mixed  by  hand  and 
may  finally  be  obtained  in  a  state  of  considerable  homogeneity. 

When  fertilizers  are  in  a  pasty  state  or  more  or  less  liquid,  they 
are  dried  at  100°,  first  introducing  a  little  oxalic  acid  in  case 
they  contain  any  volatile  ammoniacal  compounds.  The  product 
of  desiccation  is  then  passed  through  a  mill.  Before  treating  in 
this  way  it  is  necessary  to  be  sure  that  the  composition  will  not 
be  altered  by  drying.  In  the  case  of  a  mixture  containing  super- 
phosphates and  nitrate,  for  instance,  drying  would  eliminate  the 
nitric  acid.  In  such  a  case  the  free  phosphoric  acid  should  be 
neutralized  with  a  base  like  lime.  In  the  case  of  fertilizers  con- 
taining both  nitrates  and  volatile  ammoniacal  compounds,  the 
addition  of  oxalic  acid  might  also  set  free  nitric  acid  during  the 
desiccation.  In  such  a  case  it  is  necessary  to  dry  two  samples ; 
one  with  the  addition  of  oxalic  acid  for  the  purpose  of  estimating 
the  ammonia,  and  the  other  without  the  acid  for  the  purpose  of 
estimating  the  nitrate.  A  qualitative  analysis  should  precede 
all  the  operations  so  as  to  determine  the  nature  of  the  material 
to  be  operated  on. 

27.  German  Method. — In  the  method  pursued  by  the  German 
experiment  stations  the  manipulation  is  conducted  as  follows  :10 

(1)  Dry  samples  of  fertilizers  must  be  passed  through  a  sieve 
and  afterwards  well  mixed. 

(2)  With  moist  fertilizers,  which  can  not  be  subjected  to  the 
above  process,  the  preparation  should  consist  in  a  careful  and 
thorough  mixing,  without  sieving. 

(3)  On  the  arrival   of  the   samples   in   the   laboratory  their 
weight  should  be  determined.     The  half  of  the  sample  is  pre- 
pared for  analysis  and  the  other  part,  to  the  amount,  at  least,  of  a 
kilogram,  should  be  placed  in  a  glass  vessel,  closed  air-tight,  and 

"Die  landwirtschaftlichen  Versuchs-Stationen,  1891,  88  :  303. 


22  AGRICULTURAL   ANALYSIS 

left  in  a  cool  place  for  at  least  a  quarter  of  a  year  from  the  time 
of  its  reception,  in  order  that  it  may  be  subjected  to  any  sub- 
sequent investigations  which  may  be  demanded. 

(4)  In  the  case  of  raw  phosphates  and  bone-black  the  amount 
of  water  which  they  contain  should  be  determined  at  from  105°  to 
1 10°.     Samples  which  in  drying  lose  ammonia  in  any  way,  should 
have  this  ammonia  determined. 

(5)  Samples  which  are  sent  to  other  laboratories  for  control 
analyses  should  be  securely  packed  in  air-tight  glass  bottles. 

(6)  The  weight  of  the  samples    should    be    entered    in    the 
certificates  of  analysis. 

(7)  Samples  which,  on  pulverizing,  change  their  content  of 
water,  must  have  the  water  content  estimated  in  both  the  coarse 
and  powdered  condition  and  the  results  of  the  analysis  must  be 
calculated  to  the  water  content  of  the  original  coarse  substance. 

28.  Special  Cases. — Many  cases  arise  of  such  a  nature  as  to 
make  it  impossible  to  lay  down  any  rule  which  can  be  followed 
with  success.     As  in  almost  every  other  process  in  agricultural 
chemistry,  the  analyst  in  such  cases  must  be  guided  by  his  judg- 
ment and  experience.     Keeping  in  view  the  main  object,  viz.,  to 
secure  in  a  few  grams  of  material  a  fair  representation  of  large 
masses,  he  will  generally  be  able  to  reach  the  required  result  by 
following  the  broad  principles  already  outlined.     In  many  cases 
the  details  of  the  work  and  the  adaptations  necessary  to  success 
must  be  left  to  his  own  determination.     In  all  special  cases  the 
methods  of  securing  the  samples  should  accompany  the  analytical 
data. 

DRYING  SAMPLES  OF  FERTILIZERS 

29.  Difficulties  of  Desiccation. — The  determination  of  the  un- 
combined   moisture    in    a   sample   of    fertilizer    is    not   an    easv 
task.     In  some  cases,  as  in  powdered  minerals,  drying  to  con- 
stant weight  at  the  temperature    of   boiling   water   is    sufficient 
In  organic  matters  containing  volatile  nitrogenous  and  other  com- 
pounds these  must  first  be  fixed  by  oxalic  or  sulfuric  acid,  before 
the  desiccation  begins.     If  any  excess  of  sulfuric  acid  be  added, 
however,  drying  at  100°  becomes  almost  impossible.     Particular 
precautions   must  be    observed   in   drying   superphosphates.     In 


GENERAL   OBSERVATIONS  23 

drying-  samples  preparatory  to  grinding  for  analysis  it  is  best  to 
stop  the  process  as  soon  as  the  materials  can  be  pulverized.  In 
general,  samples  should  be  dried  only  to  determine  water,  and 
the  analytical  processes  should  be  performed  on  the  undried 
portions.  It  is  not  necessary,  as  a  rule,  to  dry  samples  of  mineral 
fertilizers  in  an  inert  atmosphere,  such  as  hydrogen  or  carbon 
dioxid.  Drying  in  vacuo  may  be  practiced  when  it  is  desired 
to  secure  a  speedy  desiccation  or  one  at  a  low  temperature. 

30.  Official  Methods. — The  official  agricultural  chemists  direct, 
in   the    case    of   potash   salts,    sodium    nitrate,   and    ammonium 
sulfate,  to  heat  from  one  to  five  grams  at  about  130°  until  the 
ueight  is  constant.11    The  loss  in  weight  is  taken  to  represent  the 
water.     For  all  other  fertilizers  heat  two  grams,  or  five  grams 
if  the  sample  be  very  coarse,  for  five  hours  in  a  steam  bath.     The 
international  commission  prescribes  heating  to  constant  weight 
at  100°,  using  10  grams  of  material.     Substances  containing  gyp- 
sum are  dried  for  three  hours.     Potash  salts  are  dried  in  harmony 
with  the  regulations    prescribed    by    the    potash    syndicate    at 
Leopoldshall,  Stassfurt. 

In  the  German  stations  in  the  case  of  untreated  phosphates 
and  bone-black  the  moisture  is  estimated  at  from  105°  to  110°. 
Samples  which  lose  ammonia  should  have  the  weight  of  ammonia 
given  off  at  that  temperature,  determined  separately. 

31.  General  Observations. — For  purposes  of  comparison  it  would 
be  far  better  to  have  all  contents  of  moisture  determined  at  the 
boiling  point  of  water.     While  this  varies  with  the  altitude  and 
barometric  pressure  yet  it  is  quite  certain  that  the  loss  on  drying  to 
constant  weight  at  all  altitudes  is  practically  the  same.     Where 
the  atmospheric  pressure  is  diminished  for  any  cause  the  water 
escapes  all  the  more  easily.     This,  practically,  is  a  complete  com- 
pensation for  the  diminished  temperature  at  which  water  boils. 

Only  in  the  case  where  free  sulfuric  or  phosphoric  acid  is  present 

would  this  method  be  ineffective.     The  highly  hygroscopic  nature 

of  these  acids  in  a  concentrated  state  renders  desiccation  at  such  a 

temperature  practically  impossible.     In  such  cases  a  weighed  ex- 

11  Division  of  Chemistry,  Bulletin  46,  1899  :  n. 


24  AGRICULTURAL   ANALYSIS 

cess  of  base  should  be  added  to  convert  the  acids  into  sulfates  or 
phosphates. 

Where  the  samples  contain  no  ingredient  capable  of  attacking 
aluminum,  they  can  be  conveniently  dried,  in  circular  dishes  of 
this  metal  about  seven  centimeters  in  diameter  and  one  centi- 
meter deep,  to  constant  weight,  at  the  temperature  of  boiling 
water. 

32.  Moisture  in  Monocalcium  Phosphates. — In  certain  fertilizers, 
especially  superphosphates,  containing  the  monocalcium  salt,  the 
estimation  of  water  is  a  matter  of  extreme  difficulty  on  account 
of  the  presence  of  free  acids  and  of  progressive  changes  in  the 
sample  due  to  different  degrees  of  heat. 

Stoklasa  has  studied  these  changes  and  reaches  the  following 
results  :12 

A  chemically  pure  monocalcium  phosphate  of  the  following 
composition,  viz., 

CaO 22.36  per  cent. 

P205 56.67" 

H20 21.53" 

was  subjected  to  progressive  dryings.  The  loss  of  water  after 
10  hours  was  1.83  per  cent.;  after  20  hours,  2.46  per  cent.; 
after  30  hours,  5.21  per  cent. ;  after  40  hours,  6.32  per 
cent;  after  50  hours,  6.43  per  cent.  The  loss  of  water 
remained  constant  at  6.43  per  cent.  This  loss  represents  one 
molecule  of  water  as  compared  with  the  total  molecular  magni- 
tude of  the  mass  treated.  A  calcium  phosphate,  therefore,  of 
the  following  composition,  CaH4(PO4)2.H2O  loses,  after  40 
hours  drying  at  100°,  its  water  of  crystallization.  The  calcium 
phosphate  produced  by  this  method  forms  opaque  crystals  which 
are  not  hygroscopic  and  which  give,  on  analysis,  the  following 
numbers : 

CaO 24.02  per  cent. 

P,06 60.74"         " 

H,0 15.00  "         " 

The  temperature  can  be  raised  to  105°  without  marked  change. 
"  Zeitschrift  fur  analytische  Chemie,  1890,  29  :  390. 


NATURAL   OCCURRENCE   OF    PHOSPHATES  25 

If  the  temperature  be  raised  to.  200°  the  decomposition  of  the 
molecule  is  hastened  according  to  the  following  formula  : 
4CaH4(PO4)2  =  Ca.P-A  -f  Ca(PO3)o-f  CaHoPXL  +  2H3PO4 


The  chemical  changes  during  the  drying  of  monocalcium 
phosphates  can  be  represented  as  follows,  temperature  200°  for 
one  hour: 

8[CaH4(PO4)2H2O]=4CaH4(PO4)2+Ca(PO3)2+Ca,P2O7 

+  CaH2P2O7-f  2H3PO4-h  1  2H2O. 

The  further  drying  at  200°  produces  the  following  decomposi- 
tion: 

4CaH4  (  PO4)  2+Ca  (  PO3)  2+Ca2P2O7+CaH2P2O7+2H3PO4 

=2Ca(PO3)2+4CaH2P2O7+Ca2P2O7+2H3PO4+5H2O. 

2Ca(PO3)2+4CaH2P2O7+Ca2P2O7+2H3PO4:= 

6Ca  (  PO,  )  2+2CaH2P267+5H2O. 

Finally,  pyrophosphate  at  210°  is  completely  decomposed  into 
metaphosphate  and  water  according  to  the  following  formula  : 

6Ca(PO3)2+2CaH2P2O7=8Ca(PO3),+2H2O. 
Provided  the  drying  is  made  at  once  at  210°  the  sum  of  the 
changes  produced  as  indicated  above,  can  be  represented  by  the 
following  formula  : 

8[CaH4(PO4)2.H2OJ=8Ca(PO3)2+24H2O. 
The  equations  are  to  be  considered  as  applying  only  to  a  pure 
monocalcium  salt. 

MINERAL  PHOSPHATES 

33.  Natural  Occurrence  of  Phosphates.  —  Gautier  calls  attention 
to  the  fact  that  the  oldest  phosphates  are  met  with  in  the  igneous 
rocks,  such  as  basalt,  trachyte,  etc.,  and  even  in  granite  and 
gneiss.13  It  is  from  these  inorganic  sources,  therefore,  that  all 
phosphatic  plant  food  must  have  been  drawn.  In  the  second  order 
in  age  Gautier  places  the  phosphates  of  hydro-mineral  origin.  This 
class  not  only  embraces  the  crystalline  apatites  but  also  those  phos- 
phates of  later  formation  formed  from  hot  mineral  waters  in  the 
Jurassic,  cretaceous,  and  tertiary  deposits.  These  deposits  are 
not  directly  suited  to  nourish  plants. 
13  Comptes  rendus,  1893,  116  :  1271. 


26  AGRICULTURAL   ANALYSIS 

The  third  group  of  phosphates  in  order  of  age  and  assimila- 
bility  embraces  the  true  phosphorites  containing  generally  some 
organic  matter.  They  are  all  of  organic  origin. 

In  caves  where  animal  remains  are  deposited  there  is  an  ac- 
cumulation of  nitrates  and  phosphates.  Not  only  do  the  bones 
of  animals  furnish  phosphates  but  they  are  also  formed  in  consid- 
erable quantities  by  the  decomposition  of  substituted  glycerids 
such  as  lecithin.  The  ammonia  produced  by  the  nitrification  of 
the  albuminoid  bodies  combines  with  the  free  phosphoric  acid 
thus  produced,  forming  ammonium  or  diammonium  phosphates. 
The  presence  of  ammonium  phosphates  in  guanos  was  first  noticed 
by  Chevreul. 

If  such  deposits  overlay  a  pervious  stratum  of  calcium  car- 
bonate, such  as  chalk,  and  are  subject  to  leaching,  a  double  de- 
composition takes  place  as  the  lye  percolates  through  the  chalk. 
Acid  calcium  phosphate  and  ammonium  carbonate  are  produced. 
By  further  nitrification  and  solution  the  latter  becomes  finally 
converted  into  calcium  nitrate.  In  like  manner  aluminum  phos- 
phates are  formed  by  the  action  of  decomposing  organic  matter 
on  clay. 

Davidson  explains  the  origin  of  the  Florida  phosphates  by  sug- 
gesting that  they  arose  chiefly  through  the  influx  of  animals 
driven  southward  during  the  glacial  period.14  According  to  his 
supposition,  the  waters  of  the  ocean,  during  the  cenozoic  period, 
contained  more  phosphorus  than  at  the  present  time.  The 
waters  of  the  ocean  over  Florida  were  shallow  and  the  shell  fish 
existing  therein  may  have  secreted  phosphate  as  well  as  car- 
bonate of  lime.  This  supposition  is  supported  by  an  analysis  of 
a  shell  of  lingula  ovalis,  quoted  by  Dana,  in  which  there  was 
85.79  Per  cent-  °f  nme  phosphate.  In  these  waters  were  also 
many  fishes  of  all  kinds  and  their  debris  served  to  increase  the 
amount  of  phosphatic  material.  As  the  land  emerged  from  the  sea 
came  the  great  glacial  epoch,  driving  all  terrestrial  animals  south- 
ward. There  was,  therefore,  a  great  mammal  horde  in  the 
swamps  and  estuaries  of  Florida.  The  bones  of  these  animals 
contributed  largely  to  the  phosphatic  deposits.  In  addition  to 
14  Wyatt,  Phosphates  of  America,  4th  Edition,  1892  :  66. 


NATURAL   OCCURRENCE    OF   PHOSPHATES  27 

this,  the  shallow  sea  contained  innumerable  sharks,  manatees, 
whales,  and  other  inhabitants  of  tropical  waters,  and  the  remains 
of  these  animals  added  to  the  phosphatic  store. 

While  these  changes  were  taking  place  in  the  quarternary 
period,  the  Florida  peninsula  was  gradually  rising,  and  as  soon 
as  it  reached  a  considerable  height  the  process  of  denudation  by 
the  action  of  water  commenced.  Then  there  was  a  subsi- 
dence and  the  peninsula  again  passed  under  the  sea  and  was  cov- 
ered with  successive  layers  of  sand.  The  limestone  during  this 
process  had  been  leached  by  rain  water  containing  an  excess  of 
carbon  dioxid.  In  this  way  the  limestone  was  gradually  dis- 
solved while  the  insoluble  phosphate  of  lime  was  left  in  suspen- 
sion. During  this  time  the  bones  of  the  animals  before  men- 
tioned by  their  decomposition  added  to  the  phosphate  of  lime 
present  in  the  underlying  strata,  while  some  were  transformed 
into  fossils  of  phosphate  of  lime  just  as  they  are  found  to-day  in 
vast  quantities. 

Wyatt  explains  the  phosphate  deposits  somewhat  differently.15 
According  to  him,  during  the  miocene  submergence  there  was 
deposited  upon  the  upper  eocene  limestone,  more  especially  in 
the  cracks  and  fissures  resulting  from  their  drying,  a  soft, 
finely  disintegrated  calcareous  sediment  or  mud.  The  estuaries 
formed  during  this  period  were  swarming  with  animal  and  vege- 
table life,  and  from  this  organic  life  the  phosphates  were  formed 
by  decomposition  and  metamorphism  due  to  the  gases  and  acids 
with  which  the  waters  were  charged. 

After  the  disappearance  of  the  miocene  sea  there  were  great 
disturbances  of  the  strata.  Then  followed  the  pliocene  and  ter- 
tiary periods  and  quarternary  seas,  with  their  deposits  and  drifts 
of  shells,  sands,  clays,  marls,  bowlders,  and  other  transported 
materials  supervening  in  an  era  when  there  were  great  fluctua- 
tions of  cold  and  heat. 

By  reason  of  these  disturbances  the  masses  of  the  phosphate 
deposits  which  had  not  been  infiltrated  in  the  limestone  became 
broken  up  and  mingled  with  the  other  debris  and  were  thus  de- 
posited in  various  mounds  or  depressions.  The  general  result 
16  Engineering  and  Mining  Journal,  1890,  50  :  218. 


28  AGRICULTURAL   ANALYSIS 

of  the  forces  which  have  been  briefly  outlined  was  the  formation 
of  bowlders,  phosphatic  debris,  etc.  Wyatt  therefore  classifies 
the  deposits  in  Florida  as  follows : 

1.  Original  pockets  or  cavities  in  the  limestone  filled  with  hard 
and  soft  rock  phosphates  and  debris. 

2.  Mounds  or  beaches,  rolled  up  on  the  elevated  points,  and 
chiefly  consisting  of  huge  bowlders  of  phosphate  rock. 

3.  Drift  or  disintegrated  rock,  covering  immense  areas,  chiefly 
in  Polk  and  Hillsboro  counties,  and  underlying  Peace  River  and 
its  tributaries. 

Darton  ascribes  the  phosphate  beds  of  Florida  to  the  trans- 
formation of  guano.16  According  to  this  author,  two  pro- 
cesses of  decomposition  have  taken  place.  One  of  these  is 
the  more  or  less  complete  replacement  of  the  carbonate  by  the 
phosphate  of  lime.  The  other  is  a  general  stalactitic  coating 
of  phosphatic  material.  Darton  further  calls  attention  to  the 
relation  of  the  distribution  of  the  phosphate  deposits  as  affecting 
the  theory  of  their  origin,  but  does  not  find  any  peculiar  signifi- 
cance in  the  restriction  of  these  deposits  to  the  western  ridge  of 
the  Florida  peninsula. 

As  this  region  evidently  constituted  a  long  narrow  peninsula 
during  early  miocene  time  it  is  a  reasonably  tentative  hypothe- 
sis that  during  this  period  guanos  were  deposited  from  which 
was  derived  the  material  for  the  phosphatization  of  the  limestone 
either  at  the  same  time  or  soon  after. 

Darton  closes  his  paper  by  saying  that  the  phosphate  deposits 
in  Florida  will  require  careful  detailed  geologic  exploration  be- 
fore their  relations  and  history  will  be  fully  understood. 

According  to  Dr.  N.  A.  Pratt  the  rock  or  bowlder  phosphate 
had  its  immediate  origin  in  animal  life  and  to  his  view 
the  phosphate  bowlder  is  a  true  fossil.  He  supposes  the  exist- 
ence of  some  species  in  former  times  in  which  the  shell  excreted 
was  chiefly  phosphate  of  lime.  The  fossil  bowlder,  therefore, 
becomes  the  remains  of  a  huge  foraminifer  which  had  identical 
composition  in  its  skeleton  with  true  bone  deposits  or  of  organic 
matter. 

1(1  American  Journal  of  Science,  1891,  41  :  104. 


NATURAL  OCCURRENCE   OF   PHOSPHATES  29 

Perhaps  the  most  complete  exposition  of  the  theory  of  the  re- 
covery of  waste  phosphates,  with  especial  reference  to  their  de-- 
posit in  Florida,  has  been  given  by  Eldridge.17  He  calls  atten- 
tion to  the  universal  presence  of  phosphates  in  sea  water 
and  to  the  probability  that  in  earlier  times,  as  during  the 
miocene  and  eocene  geological  periods,  the  waters  of  the 
ocean  contained  a  great  deal  more  phosphate  in  solution  than  at 
the  present  time.  He  cites  the  observations  of  Bischof,  which 
show  the  solubility  of  different  phosphates  in  waters  saturated 
with  carbon  dioxid.  According  to  these  observations  apatite 
is  the  most  insoluble  form  of  lime  phosphate,  while  artificial 
basic  phosphate  is  the  most  soluble.  Among  the  very  soluble 
phosphates,  however,  are  the  bones  of  animals,  both  fresh  and 
old.  Burnt  bones,  however,  are  more  soluble  than  bones  still 
containing  organic  'matter.  Not  only  are  the  organic  phos- 
phates extremely  soluble  in  water  saturated  with  carbon  dioxid, 
but  also  in  water  which  contains  common  salt  or  chlorid  of  am- 
monium. The  presence  of  large  quantities  of  common  salt  in 
sea  water  would,  therefore,  tend  to  increase  its  power  of  dissolv- 
ing lime  phosphates  of  organic  origin.  It  is  not  at  all  incredible, 
therefore,  to  suppose  that  at  some  remote  period  the  waters  of 
the  ocean,  as  indicated  by  these  theories,  were  much  more 
highly  charged  with  phosphates  in  solution  than  at  the  present 
time. 

According  to  Eldridge,  the  formation  of  the  hard-rock  and 
soft  phosphates  may  be  ascribed  to  three  periods:  First,  that  in 
which  the  primary  rock  was  formed;  second,  that  of  secondary 
deposition  in  the  cavities  of  the  primary  rock;  third,  that  in 
which  the  deposits  thus  formed  were  broken  up  and  the  result- 
ing fragments  and  comminuted  material  were  redeposited  as 
they  now  occur. 

"The  first  of  these  stages  began  probably  not  later  than  the 
close  of  the  older  miocene,  and  within  the  eocene  area  it  may 
have  begun  much  earlier.  Whether  the  primary  phosphate  re- 
sulted from  a  superficial  and  heavy  deposit  of  soluble  guanos, 
covering  the  limestones,  or  from  the  concentration  of  phosphate 
17  Preliminary  Sketch  of  Florida  Phosphates,  Author's  Edition  :  18. 


30  AGRICULTURAL  ANALYSIS 

of  lime  already  widely  and  uniformly  distributed  throughout  the 
mass  of  the  original  rock,  or  from  both,  is  a  difficult  question. 
In  any  event,  the  evidence  indicates  the  effect  of  the  percolation 
of  surface  waters  highly  charged  with  carbonic  and  other  acids, 
and  thus  enabled  to  carry -down  into  the  mass  of  the  limestone 
dissolved  phosphate  of  lime,  to  be  redeposited  under  conditions 
favorable  to  its  separation.  Such  conditions  might  have  been 
brought  about  by  the  simple  interchange  of  bases  between  the 
phosphate  and  carbonate  of  lime  thus  brought  together;  or  by 
the  lowering  of  the  solvent  power  of  the  waters  through  loss  of 
carbonic  acid.  The  latter  would  happen  whenever  the  acid  was 
required  for  the  solution  of  additional  carbonate  of  lime,  or 
when,  through  aeration,  it  should  escape  from  the  water.  The 
zone  of  phosphate  deposition  was  evidently  one  of  double 
concentration,  resulting  from  the  removal  of  the  soluble  car- 
bonate thus  raising  the  percentage  of  the  less  soluble  phosphate, 
and  from  the  acquirement  of  additional  phosphate  of  lime  from 
the  overlying  portions  of  the  deposits. 

"The  thickness  of  the  zone  of  phosphatization  in  the  eocene 
area  is  unknown,  but  it  is  doubtful  if  it  was  over  20  feet. 
In  the  miocene  area  the  depth  has  been  proved  from  the  phos- 
phates in  situ  to  have  been  between  six  and  12  feet." 

The  deposits  of  secondary  origin,  according  to  Eldridge, 
are  due  chiefly  to  sedimentation,  although  some  of  them  may 
have  been  due  to  precipitation  from  water.  This  secondary  de- 
position was  kept  up  for  a  long  period,  until  stopped  by  some 
climatic  or  geological  change.  The  deposits  of  phosphates  thus 
formed  in  the  Florida  peninsula  are  remarkably  free  from  iron 
and  aluminum  in  comparison  with  many  of  the  phosphates  of 
the  West  Indies. 

The  third  period  in  the  genesis  of  the  hard  rock  deposits  em- 
braces the  time  of  formation  of  the  original  deposits  and  their 
transportation  and  storage  as  they  are  found  at  the  present  time. 
The  geological  time  at  which  this  occurred  is  somewhat  uncertain 
but  it  was  probably  during  the  last  submergence  of  the  peninsula. 
In  all  cases  the  peculiar  formation  of  the  Florida  limestone 
must  be  considered.  This  limestone  is  extremely  porous  and' 


NATURAL   OCCURRENCE   OP    PHOSPHATES  31 

therefore  easily  penetrated  by  the  waters  of  percolation.  A 
good  illustration  of  this  is  seen  on  the  southwestern  and  southern 
edges  of  Lake  Okeechobee.  In  following  down  the  drainage 
canal  which  has  been  cut  into  the  southwest  shore  of  the  lake, 
the  edge  of  the  basin  which  is  composed  of  this  porous  material 
may  be  seen.  The  appearance  of  the  limestone  would  indicate 
that  large  portions  of  it  have  already  given  way  to  the  process 
of  solution.  The  remaining  portions  are  extremely  friable,  easily 
crushed,  and  much  of  it  can  be  removed  by  the  ordinary 
dredging  machines.  Such  a  limestone  as  this  is  peculiarly 
suited  to  the  accumulation  of  phosphatic  materials  due  to  the 
percolation  of  the  water  containing  them.  The  solution  of  the 
limestone  and  consequent  deposit  of  the  phosphate  of  lime  is 
easily  understood  wrhen  the  character  of  this  limestone  is  con- 
sidered. 

Shaler  as  quoted  by  Eldridge  in  the  work  already  referred  to, 
refers  to  this  characteristic  of  the  limestone  and  says  that  the 
best  conditions  for  the  accumulation  of  valuable  deposits  of  lime 
phosphate  in  residual  debris  appear  to  occur  where  the  phos- 
phatic lime  marls  are  of  a  rather  soft  character ;  the  separate  beds 
having  no  such  solidity  as  will  resist  the  percolation  of  water 
through  innumerable  incipient  joints  such  as  commonly  pervade 
stratified  materials,  even  when  they  are  of  a  very  soft  nature. 

Eldridge  is  also  of  the  opinion  that  the  remains  of  birds  are 
not  sufficient  to  account  for  the  whole  of  the  phosphatic  deposits 
in  Florida.  He  ascribes  them  to  the  joint  action  of  the  remains 
of  birds,  of  land  and  marine  animals,  and  to  the  deposition  of 
the  phosphatic  materials  in  the  waters  in  the  successive  subsi- 
dences of  the  surface  below  the  water  line. 

An  important  contribution  to  our  knowledge  of  the  origin  of 
Florida  phosphates  has  been  made  by  Dall.18  After  describing  the 
early  geological  epochs  in  the  southern  part  of  the  United  States, 
Dall  calls  attention  to  the  abundance  of  foraminifera,  whose  shells 
form  deposits  of  limestone,  which,  in  southern  Florida,  have  been 
found  to  be  nearly  2000  feet  in  thickness. 

The  deposit  of  rocks  which  is  known  geologically  as  the  Vicks- 
18  The  American  Fertilizer,  1898,  8  :  108. 


32  AGRICULTURAL   ANALYSIS 

burg  type  is  composed  entirely  of  organic  material,  that  is,  lime, 
clay,  silex  and  iron  taken  up  by  marine  animals  from  the  water  in 
which  they  lived  and  deposited  as  limestone. 

Toward  the  end  of  the  Vicksburg  epoch  a  movement  in  ele- 
vation began  which  brought  above  the  sea  level  a  part  of  the  land 
in  the  vicinity  of  Ocala,  forming  an  island  or  group  of  islands  be- 
tween Cuba  and  the  mainland,  and  the  evidence  is  very  strong 
that  these  low  islands,  containing  numerous  lagoons  of  fresh  water 
and  wooded  with  palms,  reeds  and  other  subtropical  vegetation, 
remained  as  dry  land  from  that  time  to  the  present.  At  the 
same  time  the  low  borders  of  the  continent  began  to  rise  above 
the  sea,  forming  a  coastal  plain  of  marshes  and  lagoons  inhabited 
by  tortoises,  birds  and  other  shore  animals.  It  is  well  known  that 
birds,  seals  and  similar  animals  select  for  their  rookeries,  when 
possible,  such  islets  as  those  described.  Such  locations  give  them 
security  from  predaceous  animals,  and  an  undisturbed  breeding 
place  for  their  young. 

As  phosphoric  acid  has  a  greater  affinity  for  lime  than  carbonic 
acid,  the  carbonate  of  lime  in  such  localities  became  converted 
into  the  less  soluble  phosphate  of  lime,  and  as  the  process  was 
continued  for  thousands  of  years,  in  all  probability,  the  first  steps 
in  the  formation  of  the  invaluable  phosphate  beds  of  Florida  were 
taken  in  this  way. 

34.  Character  and  Origin  of  the  Tennessee  Phosphates. — Some 
of  the  most  extensive  and  valuable  deposits  of  phosphates  in  the 
United  States  occur  in  Tennessee.  The  existence  of  these  deposits 
in  commercial  quantities  was  first  pointed  out  in  1893  and  since 
that  time  elaborate  examinations  of  the  extent  and  character  of 
the  deposits  have  been  made  by  the  U.  S.  Geological  Survey.19 

35.  Classification. — The  phosphates  of  Tennessee  are  divided 

19  Hayes,  The  Tennessee  Phosphates,  i7th  Annual  Report  of  the  Geolog- 
ical Survey,  1895-96,  Part  II  :  519. 

Hayes,  Tennessee  White  Phosphate,  2ist  Annual  Report  of  the  Geolog- 
ical Survey,  1899-1900,  Part  III :  478. 

Geological  Atlas  of  the  U.S.,  Columbia  Folio,  Tennessee. 

Hovey,  The  Production  of  Phosphate  Rock  in  1903,  Geological  Survey, 
Mineral  Resources  of  the  United  States,  1903  :  1047. 


OCCURRENCE  OF  BLACK  PHOSPHATE  33 

into  two  principal  classes  each  of  which  has  a  number  of  varieties. 
The  two  main  groups  are  designated  by  their  color,  the  black 
phosphate,  which  represents  the  original  deposition,  and  the  white 
phosphate,  which  is  a  secondary  deposition  or  replacement.  The 
first  group  belongs  to  the  Devonian  age,  and  its  members  have 
been  changed  from  their  original  form  only  by  the  process  of  con- 
solidation which  affects  all  deeply  buried  sediments ;  that  is,  they 
have  been  changed  from  a  condition  of  mud  and  sand  into  com- 
pact rock  exactly  in  the  same  manner  as  the  non-phosphatic  bodies 
above  and  below  them.  The  white  phosphates,  on  the  other  hand, 
probably  do  not  occupy  the  position  and  form  they  had  when  first 
deposited.  The  material  composing  them  has  been  translated 
from  its  original  position  and  redeposited  in  an  entirely  different 
form. 

The  white  phosphates  are  of  comparatively  recent  origin,  prob- 
ably having  been  formed  in  the  last  geological  period  preceding 
the  present. 

36.  Occurrence  of  Black  Phosphate. — The  black  phosphates  oc- 
cur first  in  a  nodular  condition  associated  with  green  sandy  shale. 
The  nodules  vary  in  size  and  shape  from  nearly  spherical  bodies 
from  one-half  to  one  and  a  half  inches  in  diameter,  to  irregular 
flattened  ellipsoids,  sometimes  two  feet  in  length  and  one-third  or 
one-quarter  as  thick.  Their  surfaces  are  smooth  and  show  no 
external  evidence  of  organic  origin.  In  weathering  they  produce 
almost  a  white  powder,  with  fine  and  concentric  banding  of  dif- 
ferent shades  of  gray.  Thin  sections  examined  under  the  micro- 
scope appear  to  be  chiefly  amorphous,  with  grains  of  pyrite  a'nd 
organic  matter.  In  some  of  the  nodules  there  is  a  concentric 
arrangement  of  the  material,  which  is  easily  separated.  The 
nodules  in  the  lower  layers  are  the  largest.  The  number  of 
nodules  varies  largely  within  short  distances.  The  nodules  con- 
tain from  60  to  70  per  cent,  of  tricalcium  phosphate.  There  is 
a  somewhat  larger  percentage  of  this  substance  in  the  weathered 
than  in  the  unweathered  rock.  The  nodules  are  easily  separated 
from  the  materials  in  which  they  are  imbedded,  so  that  even  when 
they  are  not  sufficiently  numerous  to  form  almost  continuous 
layers  they  can  be  mined  with  profit. 


34  AGRICULTURAL   ANALYSIS 

The  black  phosphate  also  occurs  in  a  bedded  form  and  presents 
several  varieties.  Among  these  may  be  mentioned  oolitic  phos- 
phate, which  has  the  appearance  of  a  rusty,  porous  sandstone. 
The  general  appearance  of  the  ovules  of  which  the  mass  is  made 
indicates  that  they  were  formed  while  lying  free  upon  the  sea 
bottom.  In  the  phosphatic  limestone  which  at  some  points  under- 
lies the  phosphate  bed,  the  same  ovules  and  rounded  fossil  casts 
are  seen  scattered  through  the  mass  of  calcite.  Another  variety 
of  this  bedded  stone  is  known  as  compact  phosphate,  resembling 
a  homogeneous,  finely  grained  sandstone.  The  phosphatic  grains 
of  this  rock  are  so  small  that  they  are  distinguished  with  diffi- 
culty even  with  a  magnifying  glass.  The  composition  of  the  rock, 
however,  is  revealed  in  a  thin  section  under  the  microscope,  and 
it  is  shown  to  be  made  up  of  small  ovules  and  fossiled  casts  closely 
packed  together.  The  ovules  are  nearly  all  flattened  and  are  ar- 
ranged with  their  long  axes  parallel. 

Another  variety  is  the  conglomerate  phosphate,  which  is  closely 
associated  with  the  oolitic  and  compact  varieties,  often  entirely 
replacing  them  and  consisting  of  beds  of  coarse  sandstone  or  con- 
glomerate containing  various  amounts  of  phosphate.  These  con- 
glomerates are  usually  black  or  gray  and  the  constituent  grains 
are  embedded  in  a  matrix  of  fine  material.  They  vary  in  size 
from  extremely  fine  grains  to  coarse  particles  one-fourth  of  an 
inch  in  diameter.  They  are  partly  phosphate  ovules,  similar  to 
those  composing  the  oolitic  rock,  and  partly  quartz.  The  con- 
glomerate also  contains  many  weather  worn  pebbles  which  are  an 
inch  or  more  in  diameter  and  composed  of  hard,  black  phosphate 
so  fine  grained  and  homogeneous  as  to  resemble  black  flint. 

There  is  also  another  variety  known  as  shaly  phosphate,  in 
which  the  laminated  structure  is  pronounced,  the  rock  splitting 
into  extremely  thin  sheets.  In  other  instances  the  layers  are  an 
inch  or  several  inches  in  thickness,  having  a  black  glazed  surface 
even  more  carbonaceous  than  the  remainder  of  the  rock. 

37.  Occurrence  of  White  Phosphates. — The  white  phosphates  ap- 
parently present  two  types;  namely,  the  breccia  and  the  bedded 
phosphate.  Closer  examination  shows  that  the  two  varieties  are 
more  nearly  related  than  was  at  first  supposed,  and  they  are  found 


LAMELLAR   PHOSPHATE  35 

grading  into  each  other  imperceptibly,  so  that  the  distinctions  which 
were  supposed  to  exist  tend  to  disappear  on  more  careful  exam- 
ination. The  result  of  this  gradual  merging  has  led  to  the  drop- 
ping of  the  original  classification  and  the  bringing  of  the  white 
phosphate  into  one  group  with  a  few  slightly  different  varieties. 
Whatever  may  have  been  the  original  form  of  this  rock,  the 
phosphatic  deposit  is  evidently  secondary  and  is  intimately  asso- 
ciated with  the  rocks  of  the  carboniferous  period.  The  sections 
of  this  variety  of  phosphatic  rock  exhibit  under  the  microscope 
masses  of  silica  in  which  are  bedded  rhombohedral  crystals,  some- 
times very  small  and  widely  scattered,  but  perfect  and  sharply 
defined.  In  the  granular  portions  of  the  rock  the  crystals  are 
larger,  appearing  as  sections  of  rhombohedrons  which  are  not 
perfectly  independent,  but  are  segregated  into  irregular  groups. 
These  crystals,  which  have  the  form  of  calcite,  have  been  en- 
tirely changed  in  their  structure  by  the  secondary  deposit.  Phos- 
phate of  lime,  in  other  words,  has  practically  taken  the  place  of 
the  carbonate  of  lime  in  these  crystals.  The  following  analyses, 
made  under  the  direction  of  Monroe,  show  the  composition  of  this 
form  of  Tennessee  white  phosphate  :20 

ANALYSES  OF  TENNESSEE  WHITE  STONY  PHOSPHATE. 

i  2               3  4               5               6 

Silica,  SiO2 61.34  49.43  54.30  54.88  50.18  56.46 

Lime,  CaO 20.30  26.40  22.87  22.76  25.57  22.01 

Phosphoric  acid,  P2O3 12.55  15-12  14.86  15.30  15.21  13.15 

Corresponding  to: 

Lime  phosphate,  Ca,  P2O8,  and..  27.40  33.00  32.45  33.40  33.20  28.60 

Lime  carbonate,  CaCO3 9.75  15.21       9.36  8.23  13.45  11.56 

38.  Breccia  Phosphate. — The  breccia  is    the    most    abundant 
variety  of  the  white  phosphate.  It  occurs  in  irregular  masses  com- 
posed of  slightly  angular  fragments  of  carboniferous  chert  im- 
bedded in  a  matrix  of  phosphate  of  lime.     The  phosphatic  matrix 
before  exposure  to  the  weather  is  of  a  white  or  slightly  reddish 
color  and  somewhat  harder  than  compact  chalk. 

39.  Lamellar  Phosphate. — Another  variety  of  the  phosphate  is 
the  white  lamellar,  consisting  of  even,  parallel  layers  or  plates.  It 

20  i7th  Annual  Report  of  the  U.  S.  Geological  Survey,   Part  II,   1895-6  : 
539- 


36  AGRICULTURAL   ANALYSIS 

lias  evidently  been  formed  by  deposition  of  solutions,  successive 
layers  being  slightly  different  in  color  and  texture.  In  numerous 
cases  the  deposition  seems  to  have  taken  place  in  a  rather  smooth 
cavity  which  was  but  partly  filled  with  the  deposited  solution,  so 
that  deposition  took  place  only  on  the  bottom. 

40.  Origin  of  the  White  Phosphates. — According  to  Hayes,  the 
white  phosphates  of  Tennessee  originated  as  follows  :21 

From  the  nature  of  the  deposits  of  white  phosphate,  their  rela- 
tions to  other  formations  of  the  region,  and  the  physical  charac- 
teristics of  the  several  varieties  of  the  rock,  there  can  be  little 
doubt  as  to  their  mode  of  deposition.  It  seems  reasonably  certain 
that  the  rock  is  entirely  a  secondary  deposit,  accumulated  subse- 
quently to  the  deposition  of  the  carboniferous,  Devonian  and  Silu- 
rian formations,  with  which  it  is  now  associated.  The  latter  were 
laid  down  on  the  sea  bottom  as  horizontal  beds  of  sand,  mud  and 
shells,  having  great  lateral  extent.  They  were  buried  beneath 
other  beds  of  sediment  many  hundred  feet  in  thickness,  which 
have  since  been  removed  by  erosion.  The  black  phosphate,  as 
has  already  been  explained,  is  one  such  sedimentary  bed  which 
was  deposited  when  the  conditions  were  favorable  for  the  accumu- 
lation of  lime  phosphate  on  the  sea  bottom.  It  was  afterwards 
deeply  buried  by  later  deposited  sediments,  and  has  been  brought 
to  light  by  elevation  of  the  sea  bottom  and  erosion  of  the  over- 
lying strata. 

Entirely  different  is  the  formation  of  the  white  phosphate. 
The  lime  phosphate  of  which  these  deposits  are  composed  was 
doubtless  originally  extracted  from  sea  water  by  organisms  and 
accumulated  together  with  other  sediments,  either  segregated  in 
beds  and  concretions  or  disseminated  through  limestones  and 
shales.  When  these  rocks  were  brought  near  the  surface  by  up- 
lift and  erosion  they  were  attacked  by  percolating  surface  waters, 
which  contain  carbonic  and  other  organic  acids.  These  acids 
readily  dissolve  carbonate  of  lime,  and  to  some  extent  also  phos- 
*l  The  Tennessee  Phosphates,  by  C.  W.  Hayes.  Abstract  from  the  iyth 
Annual  Report  of  the  Geological  Survey,  1895-6,  Part  II,  Economic  Geology 
and  Hydrography  :  356.  Also,  Extract  from  the  2ist  Annual  Report  of  the 
Geological  Survey,  1899-1900,  by  C.  W.  Hayes,  Part  III,  General  Geology, 
Ore  and  Phosphate  Deposits  :  479. 


ORIGIN   OF   THE   WHITE   PHOSPHATES  37 

phate  of  lime.  When  water  which  has  slowly  percolated  through 
the  rocks  at  some  depth  emerges  at  the  surface  or  into  a  cavity 
in  which  it  is  no  longer  subjected  to  pressure,  the  excess  of  car- 
bonic acid  escapes,  and  the  substances  which  had  been  held  in 
solution  by  means  of  that  acid  may  be  redeposited.  Thus  many 
springs  are  now  forming  about  their  exits  extensive  deposits  of 
materials  which  they  have  dissolved  in  the  course  of  their  under- 
ground passage.  The  most  common  spring  deposits  are  calcare- 
ous, although  siliceous  and  aluminous  deposits  are  not  uncom- 
mon, particularly  in  the  case  of  thermal  waters.  When  several  sub- 
stances are  held  in  the  same  solution  the  least  soluble  will  gen- 
erally be  the  first  to  separate,  and  hence  will  form  deposits  nearer 
the  exits.  Also,  when  a  solution  of  a  difficultly  soluble  substance, 
as  lime  phosphate,  comes  in  contact  with  one  which  is  more  easily 
soluble,  as  lime  carbonate,  there  is  generally  an  exchange  effected 
— the  more  soluble  substance  is  taken  up  and  the  less  soluble  one 
is  deposited  in  its  place. 

A  simple  application  of  these  principles  suggests  the  probable 
mode  of  formation  of  these  deposits.  The  altitude  at  which  they 
are  found  indicates  that  they  were  formed  when  the  valleys  of  the 
region  had  about  two-thirds  of  their  present  depth.  The  region  was 
probably  heavily  forested,  the  decay  of  vegetation  furnishing  an 
abundant  supply  of  organic  acids  to  the  percolating  surface 
waters.  It  was  also  a  region  of. sluggish  streams,  the  valleys  of 
which  may  have  been  to  some  extent  occupied  by  swamps.  The 
waters,  thus  highly  charged  with  organic  acids,  descending 
through  the  more  or  less  porous  formations  which  occupy  the 
higher  portions  of  the  country,  dissolved  calcium  carbonate,  and, 
in  less  quantity,  calcium  phosphate.  The  former,  by  reason  of  its 
greater  solubility,  was  carried  into  the  streams  and  thence  to  the 
sea.  The  phosphate,  however,  was  deposited,  the  form  of  the 
deposits  being  modified  by  local  conditions.  In  some  cases  the 
waters  containing  these  substances  in  solution  found  an  outlet  in 
a  mass  of  fragmental  chert  derived  from  the  decay  of  the  over- 
lying formations.  Under  such  conditions  the  breccia  was  formed, 
the  phosphate  merely  cementing  the  fragmental  material.  In 
other  cases  the  waters  flowed  through  open  cavities  of  consid- 


38  AGRICULTURAL   ANALYSIS 

erable  size.  When  these  were  the  interstices  among  blocks  of 
chert,  there  resulted  the  coarse  breccia.  The  cavities  were 
wholly  or  in  part  filled  with  compact  phosphate,  which  shows,  by 
differences  of  texture  and  color,  that  it  was  deposited  from  solu- 
tion in  successive  layers.  In  some  cases  it  appears  that  the  cavities 
were  in  a  pure  limestone.  After  they  had  been  to  a  greater  or 
less  extent  filled  by  the  phosphate,  by  reason  of  some  change  in 
conditions,  the  limestone  was  dissolved,  leaving  the  phosphate  dis- 
seminated through  the  residual  clay,  which  represents  the  original 
insoluble  constituents  of  the  limestone.  Finally,  in  some  places, 
instead  of  finding  open  cavities  in  which  the  phosphate  might  be 
deposited,  the  solution,  before  emerging  at  the  surface,  came  in 
contact  with  a  siliceous  limestone  under  conditions  such  that  a 
transfer  of  materials  was  effected.  The  more  soluble  carbonate 
was  taken  up  and  the  less  soluble  phosphate  was  deposited  in  its 
place.  These  conditions  gave  rise  to  the  stony  variety,  in  which 
the  phosphate  is  clearly  seen  occupying  the  place  originally  held 
by  the  carbonate. 

If  this  explanation  of  the  origin  of  these  phosphates  is  the  cor- 
rect one,  some  important  economic  conclusions  follow  as  to  the 
extent  of  the  deposits.  So  long  as  the  waters  were  percolating 
slowly  and  at  considerable  depths  they  would  take  up  rather  than 
deposit  phosphate.  They  would  find  conditions  favorable  for  the 
latter  process  only  comparatively  near  the  surface,  where  the 
excess  of  carbonic  acid  might  readily  escape.  Hence  the  deposits 
must  not  be  expected  to  extend  to  any  considerable  depth.  They 
are  essentially  superficial  pocket  deposits,  and  in  most  cases  their 
depth  will  be  limited  by  the  depth  of  the  residual  mantle  of  chert 
and  clay  with  which  they  are  so  intimately  associated.  It  seems 
probable  that  the  stony  variety  may  extend  to  greater  depths  than 
any  of  the  others,  since  the  process  to  which  it  is  attributed  is 
one  which  does  not  depend  directly  on  surface  conditions — the 
escape  of  carbonic  acid  and  the  evaporation  of  the  solution — but 
upon  some  conditions,  not  fully  understood,  favoring  replace- 
ment. 

The  deposits  were  probably  much  more  extensive  than  now. 
The  deepening  of  the  valleys  has  removed  the  greater  portion  of 


UTILIZATION   OF  THE   WHITE   PHOSPHATE  39 

the  original  deposits,  and  those  which  remain  are  merely  the  rem- 
nants which  have  accidentally  escaped  erosion. 

41.  Utilization  of  the  White  Phosphate. — From  the  foregoing 
description  of  the  several  varieties  of  white  phosphate  it  will  be 
readily  understood  that  this  rock  is  not  available  for  shipment 
without  undergoing  some  process  of  concentration.  That  a  high- 
grade  product  can  be  obtained  by  the  proper  concentration  is 
shown  from  the  numerous  analyses  of  selected  hand  specimens, 
which  sometimes  show  as  much  as  80  per  cent,  of  lime  phosphate. 
Evidently  the  method  of  treatment  should  differ  with  the  different 
varieties.  The  analyses  already  given  show  that  the  stony  variety 
contains  less  than  50  per  cent,  of  lime  phosphate,  and  in  it  the 
phosphate  is  so  intimately  associated  with  the  silica  that  no  ready 
means  of  separating  the  two  elements  suggest  themselves.  In  case 
of  the  other  two  varieties,  however,  the  problem  of  concentration 
is  a  much  simpler  one.  In  case  of  the  breccia,  the  properties  which 
may  be  taken  advantage  of  in  separating  the  chert  and  the  phos- 
phate are,  first,  differences  in  specific  gravity,  and,  second,  differ- 
ences in  hardness.  It  has  been  suggested  that  the  two  constit- 
uents of  the  rock  may  be  cheaply  separated  by  some  form  of  jig- 
ging apparatus.  Determinations  of  their  specific  gravity,  how- 
ever, do  not  offer  much  encouragement  for  this  view.  The  chert 
is  found  to  have  a  specific  gravity  varying  from  2.61  to  2.69. 
The  matrix  of  lime  phosphate  with  which  it  is  associated  has  a 
gravity  of  2.83  to  3.07.  This  difference  of  0.3  or  0.4  is  probably 
not  sufficient  for  any  simple  and  cheap  device.  The  specific 
gravity  of  the  lamellar  variety  is  somewhat  higher  than  that  of 
the  structureless  breccia  matrix. 

The  difference  in  hardness  between  the  chert  and  the  matrix 
suggests  the  possibility  of  making  a  high-grade  concentrate, 
though  not  of  making  a  complete  separation  of  the  two  constit- 
uents of  the  rock.  As  already  stated,  when  long  exposed  to  the 
atmosphere  the  matrix  becomes  considerably  indurated,  so  that  it 
is  separated  from  the  chert  with  great  difficulty.  Below  the  sur- 
face, however,  it  seems  probable  that  the  phosphate  will  generally 
be  found  soft  and  granular,  so  that  it  can  be  easily  pulverized 
and  separated  from  the  chert.  The  chert,  on  the  other  hand,  shows 


4O  AGRICULTURAL   ANALYSIS 

little  if  any  change  of  hardness  from  that  at  the  surface.  If  this 
softer  breccia,  therefore,  were  passed  through  a  suitable  crusher, 
most  of  the  phosphate  would  be  pulverized,  while  the  chert  would 
remain  in  much  larger  blocks.  If  the  material  thus  treated  were 
passed  over  a  screen  with  a  proper  mesh,  which  could  be  deter- 
mined only  by  experiments,  it  seems  altogether  probable  that  a 
fairly  complete  separation  would  be  effected.  The  process  sug- 
gested above  would  be  a  simple  and  cheap  one,  and,  considering 
the  ease  with  which  the  rock  can  be  raised,  it  seems  probable  that 
a  cheap  and  merchantable  product  could  be  obtained  in  this  man- 
ner. 

A  part  of  the  lamellar  variety  would  require  no  further  treat- 
ment than  hand  picking  at  the  bank.  The  quantity  of  such  rock, 
however,  is  probably  not  large,  and  the  greater  part  of  this  variety 
will  have  to  be  separated  from  the  clay  through  which  it  is  found 
disseminated.  This  would  probably  necessitate,  first,  screening  in 
the  bank,  to  separate  it  from  the  greater  part  of  the  clay ;  second, 
washing,  to  remove  the  remainder  of  the  clay;  and,  third,  hand- 
picking,  to  remove  the  free  chert  with  which  it  is  associated. 
None  of  these  processes  are  expensive,  and  if  careful  prospecting 
shall  show  this  variety  to  exist  in  considerable  quantities,  it  can 
doubtless  be  prepared  for  market  at  slight  expense.  It  is  im- 
portant, however,  for  the  successful  development  of  these  deposits 
that  thorough  prospecting  should  precede  the  erection  of  a  plant 
for  treating  the  rock.  The  prospecting  should  be  done  in  a  sys- 
tematic manner  and  by  a  competent  engineer. 

STATISTICS  AND  COMPOSITION 

42.  Tennessee  Phosphates. — Tennessee  produced  during  the 
year  1903,  460,530  pounds  of  phosphate  rock  containing  from 
77  to  So  per  cent,  of  lime  phosphate.  It  is  well  known  that 
almost  all  of  the  rich  phosphates  produced  in  Florida  are  ex- 
ported to  Europe.22  Of  the  rich  phosphates  produced  in  Ten- 
nessee, however,  only  about  one-fourth  are  sent  to  Europe.  The 
other  three-fourths  are  consumed  in  this  country.  The  Tennessee 
phosphates  are  not  looked  upon  with  very  great  favor  in  Europe 
because  of  their  content  of  iron  and  alumina.  Five  samples  of 
22  Annales  de  Chitnie  analytique,  1906,  1 1  :  256. 


PHOSPHATES    FROM   SOUTH   CAROLINA    DEPOSITS  41 

Tennessee  phosphate  were  found  to   have  the   following  com- 
position : 

12  34  5 

Insoluble  (silica,  etc.) 1.31  2.56  1.85  2.16  5.87 

Phosphoric  acid 36.55  36.55  35.47  35.50  32.85 

Phosphate  of  lime 79-8o  79.80  77.45  77.50  71.73 

Oxid  of  iron  and  alumina 2.00  2.48  3.16  3.88  4.52 

Carbonate  of  lime 13.27  12.05  11.46  14.29  9.93 

Organic  matters  and  water   3.62  3.11  6.08  3.17  7.95 

The  above  samples  belong  to  what  is  known  as  the  Brown  Rock 
and  come  chiefly  from  the  vicinity  of  Mt.  Pleasant  in  Maury 
County. 

43.  Blue  Phosphate. — In  Hickman  County,  which  is  adjacent  to 
Maury  County,  large  quantities  of  phosphate  rock  are  found  of 
a  bluish  gray  tint  and  less  rich  in  phosphate  of  lime  than  the  de- 
posits above  mentioned.     These  rocks  are  found  to  contain  from 
60  to  70  per  cent,  of  phosphate  of  lime,  and  from  2.5  to  5  per 
cent,  of  oxids  of  iron  and  alumina  and  from  1.5  to  5  per  cent,  of 
silica.  The  iron  exists  in  these  rocks  partly  in  the  form  of  pyrite. 
In  Perry  County  another  variety  of  phosphate  of  a  reddish  or 
white  color  is  found  with  a  still  lower  content  of  phosphate  of 
lime,  ranging  from  30  to  50  per  cent.     These  samples  come  from 
the  surface.     The  interior  deposits,  on  the  contrary,  are  quite 
rich,  containing  from  70  to  75  per  cent,  of  phosphate  of  lime. 
Still  other  deposits  are  found  in  Tennessee  containing  from  77 
to  80  per  cent,  of  phosphate  of  lime  and  from  two  to  three  per 
cent,  of  oxids  of  iron  and  alumina. 

44.  Phosphates   from   South   Carolina   Deposits. — It   has   been 
estimated  that  up  to  the  present    time    there    have    been    fur- 
nished to  the  markets  from  the  South  Carolina  deposits  about 
11,000,000  tons  of  rock,  of  which  about  one-third  has  gone  to 
Europe.     The  discovery  of  the  Florida  phosphates  was  a  severe 
blow  to  the  industry  in  South  Carolina,  the  annual  exports  from 
South  Carolina  having  fallen  to  about  30,000  tons.     The  reason 
of  this  is  that  the  South  Carolina  rocks  are  somewhat  low  in 
their  content  of  phosphate  of  lime,  ranging  between  55  and  60 
per  cent.     They  contain  from  seven  to  n  per  cent,  of  carbonate 


42  AGRICULTURAL  ANALYSIS 

of  lime,  from  eight  to  12  per  cent,  of  silica,  and  from  two  to 
four  per  cent,  of  oxids  of  iron  and  alumina. 

Small  deposits  of  phosphates  occur  in  other  parts  of  the  United 
States ;  namely,  in  North  Carolina,  in  Pennsylvania,  in  Arkansas, 
and  in  Alabama.  Lately  deposits  have  also  been  found  in  Wyo- 
ming, in  the  county  of  Uinta,  near  the  village  of  Cokeville,  which 
are  made  up  of  grayish  black  phosphates  in  the  form  of  heavy 
and  very  durable  rocks.  These  deposits  are  found  in  the  upper 
carboniferous  rocks  of  the  central  Cordilleran  region  in  a  series 
of  oolitic  beds. 

Considerable  quantities  of  phosphates  are  also  produced  in 
Canada.  The  smallness  of  the  deposits  and  the  difficulties  of 
quarrying,  however,  have  kept  the  Canada  production  down  to  a 
small  amount,  the  production  not  exceeding  30,000  tons  per  year. 
It  is  estimated  that  only  about  850,000  tons  of  phosphate  rock  are 
exported  to  Europe  from  the  United  States,  principally  from 
Florida  and  Tennessee,  Florida  leading  with  about  85  per  cent, 
of  the  total  exportations. 

45.  Magnitude  of  Product. — In  1904  the  production  of  phos- 
phates in  the  United  States,  principally  in  Florida,  Tennessee 
and  South  Carolina,  amounted  to  approximately  1,782,503  long 
tons,  valued  at  $5,703,582.  This  is  an  increase  compared  to 
1903  of  212,275  tons  in  quantity,  and  $709,670  in  value. 
Exports  in  1904,  chiefly  to  Germany,  France,  Italy  and 
Great  Britain,  totaled  about  880,000  tons  as  against  785,259 
tons  in  1903,  showing  an  increase  of  94,741  tons,  or  12 
per  cent.  The  ocean  freight  was  $2.64  to  $3.72,  equivalent  to 
from  one-third  to  one-half  of  the  c.  i.  f.  prices  paid  for  the  phos- 
phates, which  were  $9.84  to  $12.09  f°r  Florida  high-grade  rock; 
$6.39  to  $8.40  for  land  pebble ;  $9.54  to  $i  1.40  for  Tennessee  rock ; 
$5.61  to  $6.88  for  South  Carolina  rock.  In  competition  with  the 
American  phosphates  were  exports  of  775,000  tons  from  Africa, 
paying  an  ocean  freight  of  $1.44  to  $2.22,  and  selling  in  Europe 
at  $6  to  $7.60  for  Algerian,  and  $5.75  to  $6.60  for  Tunis  rock. 
There  were  also  sent  to  Europe  in  1904  some  125,000  tons  high- 
grade  phosphate  from  the  Christmas  and  Ocean  islands,  paying  a 
freight  of  about  $6.48,  and  marketed  at  $11.75  to  $!4-45  Per  ton, 


PRODUCTION   IN   THE   UNITED  STATES  43 

delivered.  Summed  up,  Europe  imported  from  the  countries 
named  a  total  of  1,780,000  tons  valued  at  approximately  $10,375,- 
683,  of  which  $5,105,650,  or  over  50  per  cent.,  represented  cost  of 
freight. 

The  domestic  trade,  which  takes  little  over  half  the  production, 
showed  some  improvement  in  1904,  and  prices  ranged  from  $6.50 
to  $7.50  per  ton  for  high-grade  rock,  f.  o.  b.  Florida  ports ;  $3.75 
to  $4  for  Florida  land  pebble ;  $4  to  $4.25  for  Tennessee  export 
rock,  f.  o.  b.  Mount  Pleasant,  and  $2.95  to  $4  for 'the  various 
domestic  grades ;  $2.75  to  $3.50  for  South  Carolina  rock,  f .  o.  b. 
Ashley  River. 

The  industry  in  Florida  is  gradually  coming  under  control  of  a 
few  large  miners,  and  the  affiliation  of  important  concerns  has 
greatly  lessened  competition  in  the  export  trade.  It  is  proposed 
tc  erect  superphosphate  plants,  to  utilize  the  large  stocks  of  70 
to  77  per  cent,  rock  in  Florida.  In  Tennessee  new  capital  has 
'been  invested  in  mining,  and  in  South  Carolina,  because  of  the 
decadence  of  the  river  industry,  work  will  be  begun  on  the 
marsh  lands  on  Morgan,  Coosaw  and  Buzzard  islands. 

Undoubtedly  the  most  gratifying  feature  of  the  phosphate  in- 
dustry to-day  is  the  gradual  elimination  of  speculative  buying,  and 
the  introduction  of  economic  management,  which  promises  better 
profits  for  the  future. 

46.  Later   Statistics. — The   latest   tabulated   statistics    relating 
to  the  phosphate  industry  in  the  United  States  are  those  found 
in  the  reports  of  the  Geological  Survey.     The  following  tables 
taken  from  those  documents  show  the  rate  of  growth  and  the 
magnitude  of  the  industry. 

47.  Production  in  the  United  States. — The  following  table  gives 
the  production  of  phosphate  rock  in  the  United  States  in  1905 
and  1906,  inclusive,  based  on  the  marketed  product,  classified  by 
kinds  or  grades  :23 

n  Geological  Survey,  Mineral  Resources  of  the  United  States,   1906  : 
1080. 


44 


AGRICULTURAL  ANALYSIS 


PRODUCTION  OF  PHOSPHATE  ROCK  IN  THE  UNITED  STATES,  1905-1906, 
BASED  ON  THE  QUANTITY  MARKETED. 


1905 

Aver- 
age 
value 
per 
ton 

$5-18 
1.98 
2.42 
3.56 

3-30 
2.92 

3-25 

3-45 
2.76 

3-13 
3.38 

1906 

Aver- 
age 
value 
per 
ton 

$5.85 
3.00 
2.8o 
4.28 

3-74 
3-'5 

3.65 

3-97 
3.22 

3-9° 
3-92 
5-65 
4.12 

State 
Florida  : 
Hard  rock 
Land  pebble  •  • 
River  pebble  •  • 
Total  

Quantity 
(long  tons) 

577,672     . 
528,587 
87,847 
1,194,106 

234,676 

35,549 
270,225 

438,139 
44,031 
689 
482,859 

Value 

$2,993,732 
1,  045,  "3 
213,000 

4,251,845 

774,447 
103,722 
878,169 

1,509,748 
121,486 
2,i55 
1,633,389 

Quantity 
(long  tons) 

587,598 
675,444 
41,463 
1,304.505 

190,180 
33,495 
223,675 

5'0,705 
35,669 

1,303 
547,677 
5,100 
2,080,957 

Value 

13,440,276 
2,029,202 
Il6,IOO 
5,585,578 

711,447 
105,621 
817,068 

2,027,917 
"4,997 
5,077 
2,147,991 
28,800 
8,579,437 

South  Carolina  : 
Land  rock  
River  rock  .... 
Total  

Tennessee  : 
Brown  rock.  •  . 
Blue  rock  
White  rock  .  .  . 
Total  

Other  States1  •  •  • 

Grand  total.    1,947,190 
1  Includes  Arkansas  and 

6,763,403 
Idaho. 

3-47 

48.  Marketed  Production. — Since  1880  the  quantity  and  the 
value  of  the  phosphate  rock  produced  (marketed)  in  the  United 
States  have  been  as  follows : 

MARKETED  PRODUCTION  (LONG  TONS)  OF  PHOSPHATE  ROCK  IN  THE 
UNITED  STATES,  1880-1906. 


Year 

Quantity 

Value 

Year 

Quantity 

Value 

1880-... 

211,377 

$1,123,823 

1894.- 

•  '        996,949 

13,479,547 

1881.... 

266,734 

1,980,259 

1895  •• 

••    1,038,551 

3,006,094 

1882.... 

332,077 

1,992,462 

1896.. 

••        930,779 

2,803,372 

1883.... 

378,380 

2,270,280 

1897.. 

••    1,039,345 

2,673,202 

1884  

431,779 

2,374,784 

1898  .  . 

..    1,308,885 

3,453,460 

1885-... 

437,856 

2,846,064 

1899.- 

••    1.515,702 

5,084,076 

1886-... 

430,549 

1,872,936 

1900.  • 

..     1,491,216 

5,359.248 

1887.... 

480,558 

1,836,818 

1901  .  . 

..    1,483,723 

5,316,403 

1888..-. 

448,567 

2,018,552 

1902.  - 

..    1,490,314 

4,693,444 

1889.... 

550,245 

2,937-776 

1903.. 

..    1,581,576 

5,319,294 

1890.... 

510,499 

3,213.795 

1904-. 

••    1,874,428 

6,580,875 

1891..-. 

587,988 

3,651,150 

1905  •• 

..    1,947,190 

6,763,403 

1892  

681,571 

3,296,227 

1906.  . 

•  •    2,080,957 

8,579,437 

1893.... 

941,368 

4,136,070 

49.  Imports. — The  following  table  shows  the  imports  of  fer- 


GENERAL   OBSERVATIONS 


45 


tilizers  of  all  kinds  into  the  United  States  for  the  years  1903- 
1906,  inclusive: 

FERTILIZERS  IMPORTED  AND  ENTERED  FOR  CONSUMPTION  IN  THE 
•UNITED  STATES,  1903-1906,  IN  LONG  TONS. 


Guano 

Kieserit  and 
Kainit 

Apatite,  bone  dust,  crude 
phosphates,  and  other 
substances  used  only 
for  manure 

S3 
4 

4 

4 

Total 
value 

,257,465 
,004,402 
,681,124 
,712,186 

Year 
1903 
1904 

1905 
1906 

Quantity 

21,985 
37,127 
27,104 
23,222 

Value 

498,702 
379,667 
322,766 

Quantity 

158,313 
218,957 
351.053 
334,843 

Value 
$    773,758 
[,050,082 
1,850,622 
1,790,969 

Quantity          Value 
246,042     $2,231,575 
243,130        2,455,618 
197,115        2,450,835 
211,274        2,598,451 

50.  World's  Production.  —  In  the  following  table  will  be  found 
a  statement  of  the  world's  production  of  phosphate  rock  from 
1903  to  1905,  inclusive. 

WORLD'S  PRODUCTION  OF  PHOSPHATE  ROCK,  1903-1905,  BY 
COUNTRIES,  IN  METRIC  TONS. 


1904 


1905 


Quantity        Value 
343,317  $1,325,104 


Quantity       Value 
334,784^1,225,126 


332,250 
8,214 


2,115,647 


23,128 

202,480 

832 


72,905 
423,521 


23,307 

193,305 

1,179 


332,292 
8,425 


i,795 


1,102 


24,120 


5,968 

8,627 

1,260,137 

423 


99,519    0) 
476,720  2,093,118 

(')        

2,522        33J6S 


Country  Quantity        Value 

Algeria 320,843  Ji, 238,454 

Aruba    ( Dutch 

West  Indies)  15, 749          (') 

Belgium 184, 1 20 

Canada 1,251 

Christmas     Is- 
land (Straits 

Settlements)  71,218 

France 475,783 

French  Guiana  7,893 

Norway 

Redonda  (Brit- 
ish West  In- 
dies)   

Russia 14,635 

Spain 1,124 

Sweden 3,219 

Tunis 352,088 

United  King- 
dom    71 

United  States. .  1,606,881 

1  Value  not  reported. 

2  Statistics  not  yet  available. 

51.  General  Observations. — The  foregoing  data  show,  as  stated 
in  the  report,  that  the  output  of  phosphate  rock  in  the  United 


3,305 

2,929 

455,197 

59 


0) 
252,263 

4,590 


1,909,859 
19,564 

10,498 


6,279 
1,582,165 

423 


1,370 
(2) 


7,295 


1,812,493 


5,319,294  1,904,418  6,580,875  1,978,345  6,763,403 


46  AGRICULTURAL  ANALYSIS 

States  in  1906  was  2,080,957  long  tons,  valued  at  $8,579,437. 
A  comparison  of  the  figures  of  late  years  indicates  that,  although 
the  output  has  usually  increased  each  year,  the  demand  has 
made  even  more  rapid  strides,  and  that  the  tendency  of  the 
market  price  is  upwards.  The  new  Western  fields  will  probably 
help  to  supply  the  increasing  demand,  but  as  their  market  is 
somewhat  local  they  will  not  materially  affect  the  general  con- 
ditions throughout  the  country.  The  demand  will  be  likely  to 
continue  in  excess  of  the  supply  unless  the  new  Tennessee  field 
proves  to  be  more  extensive  than  is  anticipated.  The  outlook 
for  the  newer  fields  is  therefore  bright  and  will  soon  become 
even  more  promising  as  the  older  fields  become  exhausted.  It 
is  not  impossible  that  the  increasing  demand  and  higher  prices 
will  make  it  possible  to  operate  many  low  grade  deposits  which 
it  has  hitherto  been  impracticable  to  utilize. 

52.  Quantity  of  Phosphoric  Acid  Removed  by  Crops. — It  is  esti- 
mated that  the  quantity  of  phosphoric  acid  removed  from  the  soil 
annually  in  the  United  States  is  equivalent  to  that  contained  in 
7,000,000  tons  of  14  per  cent,  superphosphate.24    This  estimate 
does  not  include  the  quantity  removed  by  erosion  and  leaching.  It 
is  evident  that  in  order  to  maintain  the  present  fertility  of  our 
arable  soil  in  respect  of  phosphoric  acid  about  one  million  tons  of 
this  substance,  calculated  as  P2O5,  must  be  added  to  the  soil  each 
year. 

53.  General  Conclusions. — From  the  study  of  the  origin  of  the 
deposits  of  mineral  phosphates  it  appears  that  those  which  are 
suitable  for  economic  uses  have  been  derived  chiefly  from  the 
decay  of  organic  matter — mostly  of  animal  origin.     The  phos- 
phoric acid  was  evidently  very  generally  diffused  in  the  mineral 
matter  which  first  formed  the  crust  of  the  earth.    It  began  to  be 
utilized  by  the  simplest  forms  of  vegetable  growth  which  first 
appeared  on  the  earth's  surface,  and  through  this  intermediary 
passed  into  animal  organisms.    In  these  it  was  finally  segregated 
in  the  bones  in  large  quantities.     In  the  decay  of  animal  bodies 
the  bony  structure  is  attacked  by  solvents ;  for  instance,  the  nitric 
acid  produced  by  the  oxidation  of  the  protein  of  vegetable  and 

24  Voorhees,  Journal  of  the  Franklin  Institute,  1905,  160  :  211. 


THE   VALUE   OF   BONE   MEAL  47 

animal  origin,  by  the  carbonic  acid  in  water  and  by  the  humic 
acids  of  the  soil.  The  solutions  thus  produced  are  carried  into 
the  soil  where  a  complex  series  of  actions  due  to  unstable  chem- 
ical equilibria  takes  place.  The  phosphoric  acid  which  in  the 
bones  is  combined  with  lime  as  tricalcium  phosphate,  and  which  in 
solution  is  in  the  form  of  free  acid  or  as  monocalcium  phosphate, 
tends  again  to  form  more  stable  compounds  and  is  finally  deposited 
chiefly  in  the  form  in  which  it  existed  in  the  bones,  viz.,  trical- 
cium phosphate.  All  these  changes  take  place  strictly  in  harmony 
with  the  laws  of  physical  chemistry.  The  deposits  of  phosphates, 
therefore,  are  due  to  chemical  rather  than  geological  phenomena. 

54.  The  Value  of  Bone  Meal  from  which  the  Nitrogen  Constit- 
uents Have  Been  Extracted,  as  a  Fertilizing  Reagent. — When 
fresh,  finely  ground  bones  are  applied  to  use  as  a  fertilizer  and 
valuable  results  are  obtained  they  may  be  ascribed  either  to  the 
nitrogen  constituent  in  bone  or  to  its  content  of  phosphoric  acid. 
In  general,  the  bone  phosphate  has  not  been  regarded  as  being 
of  great  value,  and  the  chief  utility  of  ground  bone  has  been 
ascribed  to  its  nitrogen  constituent.  If  the  value  of  a  phosphate 
as  a  fertilizer  be  governed  by  its  solubility  in  ammonium  citrate 
or  citric  acid,  it  has  been  shown  that  considerable  portions  of 
phosphoric  acid  in  finely  ground  bone  are  soluble  in  these  re- 
agents. 

Since  the  original  observations  of  Huston  have  shown  that  the 
phosphoric  acid  of  finely  ground  bone  is  soluble  in  ammonium 
citrate,  this  problem  has  been  studied  by  many  other  observers. 
Reitmair  has  made  investigations  on  this  subject  with  the  results 
which  follow.25  The  observations  were  carried  on  at  the  same 
time  with  degelatinized  bone  meal  and  basic  slags,  and  the  quan- 
tity of  rye  produced  per  hectare  when  these  bodies  were  used 
for  the  fertilizing  reagents  was  determined.  As  a  result 
of  these  investigations  Reitmair  concluded  that  the  solu- 
bility of  a  phosphate  in  citric  acid  is  no  criterion  for  its  value  as 
a  fertilizer  or  as  a  measure  of  its  solubility  in  the  soil.  The  solu- 
bility in  citric  acid  of  phosphate  is  no  measure  for  the  quantities 
of  the  active  forms  of  phosphoric  acid  which  are  given.  It  is 
15  Wiener  landwirtschaftliche  Zeitung,  1905,  55  :  879-881  and  889-891. 


48  AGRICULTURAL   ANALYSIS 

not  even  a  measure,  as  has  often  been  supposed,  of  the  favorable 
mechanic  properties  of  phosphatic  manure.  The  larger  particles 
of  bone  phosphate  and  of  basic  slags  were  brought  into  solution 
both  by  the  usual  and  by  •  the  modified  digestion  methods  prac- 
ticed. Various  samples  of  the  bone  meal  from  different  sources 
were  treated  with  citric  acid,  according  to  the  usual  method,  to 
determine  the  percentage  of  solubility  therein,  and  the  quantity 
of  fine  particles,  passed  through  a  sieve  with  fine  mesh,  was  de- 
termined. A  bone  meal  containing  86.5  per  cent,  of  fine  particles 
showed  a  solubility  of  92.3  per  cent,  in  citric  acid,  while  the  de- 
gelatinized  sample  of  bone  meal  containing  only  12.6  per  cent,  of 
fine  particles  showed  a  solubility  of  87.6  per  cent.  Thus,  while 
it  is  generally  true  that  the  solubility  in  citric  acid  varies  inversely 
with  the  size  of  the  particles,  it  does  not  vary  proportionately 
thereto.  The  period  of  digestion  in  each  case  was  one-half  hour. 

It  is  evident  from  the  above  that  the  agricultural  chemist  has 
yet  much  to  learn  concerning  the  character  and  speed  of  the  solu- 
tion of  phosphate  in  a  soil.  The  changes  which  take  place  in  the 
ordinary  digestion  in  citric  acid  in  the  laboratory  are  evidently 
of  a  very  different  degree  of  magnitude  and  are  carried  on  with 
a  very  different  degree  of  speed  from  that  which  takes  place  dur- 
ing the  growing  period  in  the  soil  itself. 

All  the  experiments  conducted  by  Reitmair  indicate  that  the 
degelatinized  phosphoric  acid  has  a  distinct  value  as  a  phosphatic 
fertilizer  and  this  depends  primarily  upon  the  state  of  subdivision 
and  is  indicated  only  approximately  by  its  solubility  in  citric  acid. 
Attention,  however,  must  be  called  to  the  fact  that  in  the  manu- 
facture of  degelatinized  bone  meal  it  has  not  yet  been  possible  to 
produce  a  product  entirely  free  from  nitrogen  on  a  commercial 
scale.  The  last  traces  of  nitrogen  are  not  removed  and 
there  usually  remains  in  the  degelatinized  bone  about 
0.5  per  cent,  of  nitrogen.  This  residue  must  be  re- 
garded as  an  unavoidable  contamination  of  the  bone 
meal  for  experimental  purposes,  but  it  is  of  a  magnitude  so 
small  as  to  be  practically  ignored  in  the  experimental  work.  It  is 
evident,  therefore,  that  any  attempt  to  determine  the  fertilizing 
value  either  of  degelatinized  bone  or  of  basic  slag  by  its  solubility 


CONSTITUENTS   TO    BE    DETERMINED  49 

in  citric  acid  solutions  is  likely  to  lead  to  erroneous  conclusions. 
Moreover,  the  fertilizing  value  of  any  material  of  this  kind  is 
not  a  constant  quantity,  but  varies  always  with  the  character  of 
the  soil  to  which  it  is  applied  and  of  the  seasonal  environment  to 
which  it  is  subjected.  The  chemist  has  done  all  that  could  be 
reasonably  expected  of  him  when  he  has  determined  the  fineness 
of  the  subdivisions  of  the  material  and  its  relative  solubility  in 
certain  reagents  which  indicate  the  relative  amount  of  acid  pres- 
ent which  readily  passes  into  solution  under  the  ordinary  condi- 
tions to  which  it  is  likely  to  be  subjected.  It  must  be  remem- 
bered, however,  that  in  the  field  the  processes  of  solution  go  on 
constantly  for  a  period  of  three  or  four  months;  in  fact,  as 
long  as  the  plant  continues  feeding.  A  very  feeble  solubility  in 
the  soil,  therefore,  would  render  the  phosphoric  acid  constantly 
available  in  the  proportion  in  which  it  is  used.  If  a  reagent  of 
the  same  feeble  power  was  used  in  the  laboratory  it  would  neces- 
sarily have  to  be  kept  in  activity  over  a  long  period  of  time  to 
yield  results  which  are  comparable  to  those  found  in  the  soil. 
Therefore,  it  seems  only  reasonable  to  use  a  stronger  reagent 
for  a  limited  period  of  time  such  as  can  be  used  practicably  by 
the  analyst  for  his  determinations. 

While  the  use  of  the  various  reagents  which  have  been  pro- 
posed for  the  valuation  of  these  materials  may  not  lead  to  results 
directly  comparable  to  those  that  take,  place  in  the  growing  sea- 
son, they  do,  undoubtedly,  give  an  idea  of  the  availability,  which 
is  of  great  practical  importance. 

ANALYTICAL  PROCESSES 

55.  Constituents  to  be  Determined. — The  most  important  point 
in  the  analysis  of  mineral  phosphates  is  to  determine  their  con- 
tent of  phosphoric  acid.  Of  equal  scientific  interest,  however, 
and  often  of  great  commercial  importance  is  the  determination 
of  the  percentage  of  other  acids  and  bases  present.  The  analyst 
is  often  called  on,  in  the  examination  of  these  bodies,  to  make 
known  the  content  of  water  both  free  and  combined,  of  organic 
and  volatile  matter,  of  carbon  dioxid,  sulfur,  chlorin,  fluorin, 
silica,  iron,  alumina,  calcium,  manganese,  magnesia,  and  the  al- 
kalies. The  estimation  of  some  of  these  bodies  presents  problems 


50  AGRICULTURAL   ANALYSIS 

of  considerable  difficulty,  and  it  would  be  vain  to  suppose  that  the 
best  possible  methods  are  now  known.  Especially  is  this  the  case 
with  the  processes  which  relate  to  the  estimation  of  the  fluorin, 
silica,  iron,  alumina,  and  lime.  The  phosphoric  acid,  however, 
which  is  the  chief  constituent  from  a  commercial  point  of  view, 
it  is  believed,  can  now  be  determined  with  a  high  degree  of  pre- 
cision. Often  the  estimation  of  some  of  the  less  important  con- 
stituents is  of  great  interest  in  determining  the  origin  of  the  de- 
posits, especially  in  the  case  of  fluorin.  While  the  merchant  is 
content  with  knowing  the  percentage  of  phosphoric  acid  and  the 
manufacturer  asks  in  addition  only  some  knowledge  of  the  quan- 
tity of  iron,  alumina,  and  lime,  the  analyst  in  most  cases  is  only 
content  with  a  complete  knowledge  of  the  constitution  of  the 
sample  at  his  disposal. 

56.  Dissolving  the  Phosphoric  Acid. — It  often  happens,  in  the 
case  of  a  mineral  phosphate,  that  the  only  determination  desired 
is  of  the  phosphoric  acid.  In  such  a  case  the  analyst  may  pro- 
ceed as  follows:  If  the  qualitative  test  shows  the  usual  amount 
of  phosphoric  acid,  two  grams  of  the  sample  passed  through  a 
sieve,  with  a  millimeter,  or,  better,  a  half  millimeter  mesh,  are 
placed  in  a  beaker  and  thoroughly  moistened  with  water.  The 
addition  of  water  is  to  secure  an  even  action  of  the  hydrochloric 
acid  on  the  carbonates  present.  The  beaker  is  covered  with  a 
watch-glass  and  a  little  hydrochloric  acid  is  added  from  time  to 
time  until  all  effervescence  has  ceased.  There  are  then  added 
about  30  cubic  centimeters  of  aqua  regia  and  the  mixture  is  raised 
to  the  boiling-point  on  a  sand-bath  or  over  a  lamp.  The  heating 
is  continued  until  chlorin  is  no  longer  given  off  and  solution  is 
complete.  The  volume  of  the  solution  is  then  made  up  to  200 
cubic  centimeters  without  filtering,  filtered,  and  an  aliquot  part 
of  the  filtrate,  usually  50  cubic  centimeters,  representing  half  a 
gram  of  the  original  sample,  used  for  the  determination  of  the 
phosphoric  acid  according  to  some  one  of  the  accredited  methods. 
The  small  quantity  of  insoluble  material  from  phosphates  of  the 
usual  composition  does  not  introduce  any  appreciable  error  into 
the  process  when  the  volume  is  made  up  to  200  or  250  cubic 
centimeters. 


CONDUCT  OF  THE   INCINERATION  51 

INCINERATION   IN    A    MIXTURE  OF  SULFURIC  AND 
NITRIC  ACIDS 

57.  Destruction  of  Organic  Matter. — The  preliminary  destruc- 
tion of  the  organic  matter  for  the  purpose  of  determining  the 
phosphoric  acid  and  other  mineral  matters,  save  sulfur  and  nitro- 
gen, may  be  conveniently  conducted  as  follows : 

Neumann  has  proposed  incineration  in  a  mixture  of  sulfuric 
and  nitric  acids  as  a  convenient  method  of  preventing  the  forma- 
tion of  free  carbon,  which  is  destroyed  very  slowly  by  subsequent 
burning.26  The  acid  mixture  is  prepared  by  pouring  slowly 
and  with  constant  shaking,  one-half  liter  of  concentrated  sul- 
furic acid  into  one-half  liter  of  concentrated  nitric  acid  of  a 
specific  gravity  of  1.4. 

58.  Apparatus. — The  incineration  is  carried  on  in  a  deep,  round 
flask  of  Jena  glass  which  has  the  normal  length  of  neck  of  about 
10  centimeters  and  a  capacity  of  from  one-half  to  three-fourths 
of  a  liter.  Over  this  is  placed  in  a  glass  or  porcelain  ring  a  funnel 
provided  with  a  stop-cock,  which  is  conveniently  provided  with 
a  capillary  dropping-tube,  and  the  whole  apparatus  is  fixed  to  an 
appropriate  stand.     In  the  preparation  of  the  sample  different 
processes  are  employed,  according  to  the  condition  of  the  sam- 
ple.    Dry,  powdery  substances  are  placed  in  small  glass  tubes 
(weighing  tubes)  which  can  be  easily  passed  into  the  neck  of  the 
incineration  flask.     Sticky  substances  can  be  placed  in  a  piece  of 
a  broken  test-tube.    Liquids  can  be  placed  in  thin,  weighed,  small 
tubes  which  are  easily  broken  after  placing  in  the  flask.    Dry  or 
moist  substances  can  be  used  for  the  incineration,  and  even  liquids 
in  not  too  large  quantities,  without  any  previous  preparation.     In 
the  case  of  blood  it  is  better  to  evaporate  it  before  incineration. 
Fats  or  materials  rich  in  carbohydrates,  such  as  milk,  should  be 
treated  before  incineration  with  one  per  cent,  of  pure  potash  lye 
and  evaporated  to  a  sirupy  consistence  in  order  to  avoid  foaming 
or  bumping  in  the  flask.     For  instance,  for  25  cubic  centimeters 
of  milk  about  15  cubic  centimeters  of  one  per  cent,  potash  lye 
are  used. 

59.  Conduct  of  the  Incineration. — The  substance  which  has  been 
16  Zeitschrift  fur  physiologische  Chemie,  1902-3,  37  :  115- 


52  AGRICULTURAL   ANALYSIS 

prepared  in  some  of  the  ways  described  is  placed  in  the  flask  and 
a  measured  quantity  of  the  acid  mixture,  from  five  to 
10  cubic  centimeters,  poured  over  it  and  warmed  with  a 
moderate  flame.  As  soon  as  the  evolution  of  brown 
nitroso-vapors  becomes  slow  a  further  addition  of  the 
acid  mixture,  drop  by  drop,  from  the  funnel  furnished  with 
a  stop-cock,  is  added  and  this  addition  continued  until  the  re- 
action ceases  and  the  intensity  of  the  brown  vapors  evolved  is 
diminished.  In  order  to  determine  whether  the  destruction  of 
the  material  has  been  completed,  the  addition  of  the  acid  mixture 
is  discontinued  for  a  short  time  and  the  mass  further  heated  until 
the  brown  vapors  formed  disappear  and  it  is  noticed  whether 
the  liquid  in  the  flask  is  still  dark  or  black.  If  this  is  the  case 
the  acid  mixture  is  again  added  and  the  test  above 
described,  after  a  few  minutes,  is  repeated.  If  on  standing 
and  after  the  expulsion  of  the  brown  vapors  the  bright 
yellow  or  colorless  liquid  is  not  again  darkened  by  further  heat- 
ing, and  also  no  evolution  of  gas  is  observed,  the  incineration  may 
be  regarded  as  complete.  If  the  liquid  is  colored  slightly  yellow 
it  generally  becomes  completely  clear  on  cooling.  Three  times 
as  much  water  is  now  added  as  the  quantity  of  acid  mixture 
which  has  been  used,  the  mixture  heated  and  boiled  from  five  to 
10  minutes.  By  this  process  brown  vapors  are  evolved  which 
are  derived  from  the  decomposition  of  the  nitrosyl  sulfuric  acid 
which  has  been  formed. 

It  must  be  remembered  that  in  the  above  operation  the  nitro- 
gen of  the  protein  matter  is  not  converted  into  ammonia.  In 
fact,  no  trace  of  ammonia  can  be  found  in  the  resulting  liquid. 
The  ash  constituents,  however,  of  the  organic  matter  are  found 
in  a  completely  inorganic  state  dissolved  in  the  mixture,  and  this 
mixture  can  be  used  for  the  determination  of  these  constituents 
in  the  ordinary  way. 

The  above  method  for  freeing  the  phosphorus  and  converting 
it  into  inorganic  forms  has  given  good  results  in  the  laboratory 
of  the  Bureau  of  Chemistry. 

60.  Loss  of  Phosphoric  Acid  by  Incineration. — It  is  well  known 
that  in  certain  substances  used  for  fertilizing  purposes,  such  as 


LOSS   OF   PHOSPHORIC   ACID   BY   INCINERATION  53 

oil  cakes  and  other  organic  compounds,  the  large  quantity  of 
phosphoric  acid  which  they  contain  is  in  organic  combination 
and  unless  special  precautions  are  exercised  a  portion  of  the 
phosphorus  is  lost  in  burning.  The  loss  of  phosphoric  acid  which 
takes  place  in  cereals  has  lately  been  carefully  studied  by  Leavitt 
and  LeClerc.27  In  the  case  of  wheat  it  is  shown  that  the 
principal  part  of  the  organic  phosphorus  is  in  a  water-soluble 
form,  known  as  phytin.  This  substance  has  a  relatively  high 
molecular  weight  compared  to  the  phosphorus  molecule.  A 
comparatively  large  percentage  of  the  phosphorus  may  be  lost 
in  ashing  without  changing  very  greatly  the  apparent  weight  of 
the  ash. 

As  is  well  known,  the  addition  of  calcium  acetate  previous  to 
burning  prevents  the  volatilization  of  phosphoric  acid.  The  pro- 
portion of  phosphorus  lost  by  the  ordinary  incineration  as  com- 
pared with  the  amount  obtained  with  the  previous  addition  of 
calcium  acetate  has  been  found  in  the  extreme  cases  to  be  50  per 
cent,  of  the  total  quantity  present.  The  ordinary  incineration 
was  conducted  at  redness.  If,  however,  the  incineration  is  ac- 
complished without  any  treatment  whatever  at  incipient  redness 
just  sufficient  to  show  a  faint  radiation  of  light  from  the  dishes, 
there  is  no  appreciable  loss  of  phosphoric  acid.  The  results 
show  that  the  ashing  below  the  point  of  fusion  of  the  mineral 
portions  of  the  ash  is  not  a  very  important  factor  where  only  the 
percentage  of  ash  is  desired.  But  in  order  to  determine  the 
quantity  of  the  phosphorus  as  phosphoric  acid  the  greatest  cau- 
tion must  be  observed  to  keep  the  temperature  below  the  volatil- 
ization point  of  the  combined  phosphorus.  This  is  to  be  ac- 
complished either  by  incineration  at  an  extremely  low  tempera- 
ture or  by  previous  treatment  with  calcium  acetate. 

Later  investigations  show  that  in  reality  there  is  no  appreciable 
loss  of  phosphoric  acid  even  at  bright  redness.  The  phosphoric 
acid  is  simply  changed  into  a  form  which  is  not  precipitable  by 
ammonium  molybdate  until  the  ash  has  been  boiled  a  long  time 
with  nitric  acid,  or  has  been  treated  according  to  Neumann's 
method  of  digesting  with  nitric  and  sulfuric  acid. 

27  Journal  of  the  American  Chemical  Society,  1908,  30  :  391,  617. 


54  AGRICULTURAL   ANALYSIS 

61.  Official  Method. — The  official  chemists  recommend  seven 
methods  of  solution  for  mineral  phosphates,  phosphatic  materials 
and  preparations  thereof;  viz.,28 

1.  Ignite  and  dissolve  in  hydrochloric  acid. 

2.  Evaporate  with  five  cubic  centimeters  of  magnesium  nitrate 
solution  and  dissolve  in  hydrochloric  acid.     This  method  is  ap- 
plicable in  the  presence  of  organic  matter. 

3.  Boil  with  from  20  to  30  cubic  centimeters  of  strong  sulfuric 
acid,  adding  from  two  to  four  grams  of  sodium  or  potassium 
nitrate  at  the  beginning  of  the  digestion  and  a  small  quantity, 
after  the  solution  has  become  nearly  colorless.     Or  the  nitrate  in 
small  quantities  may  be  added  at  regular  intervals  during  the 
whole  time  of  the  digestion,  which  is  conducted  in  a  kjeldahl 
flask  marked  at  250  cubic  centimeters.     When  the   solution  is 
colorless  add   150  cubic  centimeters  of  water,  boil   for  a  few 
minutes,  cool  and  make  up  to  the  mark  with  water. 

4.  Digest  with  strong  sulfuric  acid  and  such  other  reagents  as 
are  used  in  the  processes  for  converting  nitrogen  in  nitrogenous 
compounds  into  sulfate  of  ammonia  as  described  in  the  second  part 
of  this  volume.     Do  not  add  any  potassium  permanganate  but 
after  the  solution  has  become  colorless  add  about  100  cubic  centi- 
meters of  water,  boil  for  a  few  minutes,  cool  and  make  up  to  a 
convenient  volume  (250  cubic  centimeters).    The  operation  should 
be  conducted  on  about  2.5  grams  of  substance. 

Processes  3  and  4  are  especially  applicable  to  organic  sub- 
stances such  as  oil  cakes,  which  contain  considerable  quantities 
of  phosphorus. 

5.  Dissolve  in  30  cubic  centimeters  of  concentrated  nitric  and  a 
small  quantity  of  hydrochloric  acid  and  boil  until  organic  matter 
is  destroyed. 

6.  Add  to  the  substance  30  cubic  centimeters  of  concentrated 
hydrochloric  acid,  heat  and  add  cautiously  in  small  quantities  at 
a  time  about  0.5  gram  of  finely  pulverized  potassium  chlorate  to 
destroy  organic  matter. 

7.  Dissolve  the  substance  in  from  15  to  30  cubic  centimeters  of 
strong  hydrochloric  acid  and  from  three  to  10  cubic  centimeters 

w  Bureau  of  Chemistry,  Bulletin  107,  1907  :  2. 


PRELIMINARY  CONSIDERATIONS  55 

of  nitric  acid.    This  method  is  particularly  suited  to  samples  con- 
taining much  iron  or  aluminum  phosphate. 

From  the  above  directions  it  is  seen  that  in  a  purely  mineral 
phosphate  a  single  strong  acid  or  a  mixture  of  acids  is  sufficient 
to  bring  all  the  phosphoric  acid  into  solution.  Where  organic 
matter  is  present  the  use  of  strongly  oxidizing  solvents  as  in 
4  and  5  is  necessary.  In  substances  containing  phosphorus  in 
organic  forms  such  as  blood,  tankage,  oil  cakes,  seeds,  etc.,  espec- 
ial care  is  required  to  complete  the  oxidation  and  secure  all  the 
phosphorus  in  the  form  of  phosphoric  acid. 

GENERAL    METHODS   FOR   ESTIMATING  PHOSPHORIC 
ACID  IN  FERTILIZERS 

62.  Preliminary  Considerations. — The  chief  sources  of  the 
phosphoric  acid  in  commercial  fertilizers  are  the  mineral  phos- 
phates and  bones.  In  respect  of  the  general  analyses  of  mineral 
phosphates  detailed  directions  have  been  given  in  the  preceding 
volume.  Bones  are  valuable  for  fertilizing  materials,  both  because 
of  their  content  of  phosphoric  acid  and  of  their  organic  nitrogen. 
The  method  of  treating  bones  for  their  phosphoric  acid  will  be 
found  in  the  general  methods  for  fertilizing  materials,  and  their 
nitrogen  content  can  be  determined  by  the  processes  to  be  de- 
scribed hereafter.  Other  fertilizing  materials  also  contain  phos- 
phorus, as  ashes,  tankage,  oil  cakes,  and  other  organic  products. 
In  general,  the  methods  for  determining  the  phosphoric  acid  is 
the  same  in  all  cases,  but  the  means  of  destroying  the  organic 
matter  precedent  to  the  analysis  vary  in  different  cases.  In  most 
cases  a  simple  ignition  is  sufficient,  while,  if  the  phosphorus  be 
found  in  certain  organic  products,  the  oxidation  must  be  accom- 
plished by  one  of  the  methods  described  in  the  processes  adopted 
by  the  official  chemists.  In  all  cases  of  acid  phosphates 
and  superphosphates,  the  water  and  ammonium  citrate-soluble 
phosphoric  acid  is  to  be  determined  as  well  as  the  total.  In 
basic  slags  the  amount  soluble  in  ammonium  citrate  or  dilute 
citric  acid  is  also  to  be  ascertained. 

In  all  cases  where  soluble  or  so-called  reverted  acid  is  to  be 
considered,  the  analysis  must  be  performed  without  previous 
desiccation  or  ignition.  If  water  content  or  loss  on  ignition  is 


56  AGRICULTURAL   ANALYSIS 

to  be  considered,  the  operation  to  determine  them  must  be  con- 
ducted on  a  separate  part  of  the  sample. 

The  methods  of  analysis  which  have  been  adopted  by  associa- 
tions of  chemists  should  be  given  the  preference  in  the  conduct  of 
the  work,  although  it  must  be  admitted  that  they  may  contain 
sources  of  error,  and  may  be  in  no  respect  superior  to  processes 
employed  by  chemists  in  their  private  capacity.  In  this  country 
the  methods  adopted  by  the  Association  of  Official  Agricultural 
Chemists  should  be  followed  as  closely  as  possible.  The  great 
merit  of  other  methods,  however,  must  not  be  denied.  Espe- 
cially those  methods  which  shorten  the  time  required  or  diminish 
the  labor  and  expense  of  the  analysis  are  worthy  of  careful  con- 
sideration. In  factory  work,  for  instance,  it  is  often  far  more 
important  for  the  chemist  to  be  able  to  rapidly  determine  the 
phosphoric  acid  in  a  great  number  of  samples  with  approximate 
accuracy  than  to  confine  his  work  to  one  with  absolute  precision. 
Some  of  the  shorter  methods,  moreover,  notably  the  citrate  or  ti- 
tration  process,  appear  to  be  quite,  if  not  altogether,  as  reliable 
as  the  molybdate  method,  while  in  the  case  of  the  uranium  volu- 
metric process,  it  must  not  be  forgotten  that  it  has  been  largely 
practiced  in  France.  Other  volumetric  processes  are  given 
in  full,  as,  for  instance,  the  one  perfected  by  Pemberton  and  Kil- 
gore,  and  data  are  at  hand  to  justify  their  strong  recommendation. 
It  should  be  remembered  that  this  manual  is  not  written  for  the 
beginner,  but  rather  for  the  chemist  already  acquainted  with  the 
principles  and  practice  of  general  chemical  analysis,  and  it  is, 
therefore,  expected  that  each  analyst  will  make  intelligent  use  of 
the  data  placed  at  his  disposal. 

63.  Preparation  of  Reagents. — Ammonium  Citrate  Solution. — 
(a)  Mix  370  grams  of  commercial  citric  acid  with  1500  cubic 
centimeters  of  water,  nearly  neutralize  with  commercial  ammonia, 
cool,  add  ammonia  until  exactly  neutral  (testing  with  saturated 
alcoholic  solution  of  corallin)  and  bring  to  a  volume  of  two  liters. 
Determine  the  specific  gravity,  which  should  be  1.09  at  20°,  be- 
fore using. 

(&)  Optional  Method. — To  370  grams  of  commercial  citric 
.acid  add  commercial  ammonia,  of  0.96  specific  gravity,  until  near- 


PREPARATION    OF   REAGENTS  57 

ly  neutral ;  reduce  the  specific  gravity  to  nearly  i  .09  and 
proceed  as  follows :  Prepare  a  solution  of  fused  calcium 
chlorid  200  grams  to  the  liter,  and  add  four  volumes  of 
strong  alcohol.  Make  the  mixture  exactly  neutral,  using  a 
small  amount  of  freshly  prepared  corallin  solution  as  a  prelimi- 
nary indicator,  withdrawing  a  portion,  diluting  with  an  equal 
volume  of  water,  and  testing  with  cochineal  solution.  Fifty  cubic 
centimeters  of  this  solution  will  precipitate  the  citric  acid  from 
10  cubic  centimeters  of  the  citrate  solution.  To  10  cubic  centi- 
meters of  the  nearly  neutral  citrate  solution  add  50  cubic  centi- 
meters of  the  alcoholic  calcium  chlorid  solution,  stir  well,  filter 
at  once  through  a  folded  filter,  dilute  with  an  equal  volume  of 
water  and  test  the  reaction  with  neutral  solution  of  cochineal.  If 
acid  or  alkaline,  add  ammonia  or  citric  acid,  as  the  case  may  be,  to 
the  citrate  solution,  mix,  and  test  again  as  before.  Repeat  this  pro- 
cess until  a  neutral  reaction  of  the  citrate  solution  is  obtained. 
The  specific  gravity  must  be  1.09  at  20°. 

The  reagents  employed  in  the  separation  of  the  phosphoric 
acid  are  prepared  according  to  the  following  formulas: 

Molybdate  Solution. — Dissolve  100  grams  of  molybdic  acid  in 
144  cubic  centimeters  of  ammonia,  specific  gravity  0.90,  and  271 
cubic  centimeters  of  water ;  pour  the  solution  thus  obtained,  slow- 
ly and  with  constant  stirring,  into  489  cubic  centimeters  of  nitric 
acid,  specific  gravity  1.42,  and  1148  cubic  centimeters  of  water. 
Keep  the  mixture  in  a  warm  place  for  several  days,  or  until  a 
portion  heated  to  40°  deposits  no  yellow  precipitate  of  ammo- 
nium phosphomolybdate.  Decant  the  solution  from  any  sedi- 
ment and  preserve  it  in  glass-stoppered  vessels. 

Ammonium  Nitrate  Solution. — Dissolve  200  grams  of  com- 
mercial ammonium  nitrate  in  water  and  dilute  with  water  to  two 
liters. 

Magnesia  Mixture. — Dissolve  22  grams  of  recently  ignited 
calcined  magnesia  in  dilute  hydrochloric  acid,  avoiding  an  ex- 
cess of  the  latter.  Add  a  little  calcined  magnesia  in  excess,  and 
boil  a  few  minutes  to  precipitate  iron,  alumina,  and  phosphoric 
acid ;  filter ;  add  280  grams  of  ammonium  chlorid,  700  cubic  centi- 
meters of  ammonia  of  specific  gravity  0.96,  and  water  enough  to 


58  AGRICULTURAL   ANALYSIS 

make  a  volume  of  two  liters.  Instead  of  the  solution  of  22  grams 
of  calcined  magnesia,  1 10  grams  of  crystallized  magnesium  chlorid 
(MgCl2.6H2O)  may  be  used. 

Dilute  Ammonia  for  Washing. — This  solution  is  prepared  so 
as  to  contain  2.5  per  cent.  NH3. 

Magnesium  Nitrate  Solution. — Dissolve  320  grams  of  cal- 
cined magnesia  in  nitric  acid,  avoiding  an  excess  of  the  latter; 
then  add  a  little  calcined  magnesia  in  excess ;  boil ;  filter  from  the 
excess  of  magnesia,  ferric  oxid,  etc.,  and  dilute  with  water  to  two 
liters. 

Formulas  for  the  Reactions. — The  reactions  which  take  place 
when  a  mineral  acid,  for  instance,  nitric,  dissolves  tricalcium 
phosphate,  may  be  represented  as  follows:  Ca3(PO4)2-f-4HNO3 
=:Ca(H2PO4)2-{-2Ca(NO3)2.  In  the  case  of  a  large  excess  of 
acid,  free  phosphoric  acid  may  be  formed  thus : 

Ca3(P04)2+6HN03=3Ca(N03)2+2H8P04. 
Assuming  that  the  phosphoric  acid  is  in  a  soluble  state  in  the 
solutions  prepared  with  the  strong  hot  acids,  the  reactions  which 
take  place  in  the  process  of  separating  it  are  as  follows : 

1.  (For  free  phosphoric  acid)  : 

2H3PO4+24  ( NH4)  2MoO4+42HNO3=2  ( NH4)  SPO4.  i2MoO, 
+42NH4NO3-f24H2O. 

2.  (For  monocalcium  phosphate)  : 
Ca(H2PO4)2+24(NH4)2MoO4+44HNO3=2(NH4)3PO4. 

i2MoO3+Ca(NH3)2+42NH4NO3+24H2O. 
The  yellow  precipitate  2(NH4)3PO4.i2MoO3  is  dissolved  in 
ammonia  with  regeneration  of  ammonium  molybdate  as  follows : 

3.  2(NH4)3PO4.i2MoO3+48NH4OH=2(NH4)sPCVr- 

24  ( NH4 )  2MoO4+24H2O. 

4.  Precipitation  of  the  phosphoric  acid  with  magnesia  salts: 

(NH4)8PO4+MgCl2=NH4MgP04-fNH4Cl. 

5.  Conversion  of  the  ammonia-magnesium  phosphate  into  mag- 
nesium pyrophosphate  by  heat: 

2NH4MgP04=Mg1P10T+2NH,+HfO. 
The  factors  for  calculating  the  phosphorus  pentoxid  and  tri- 


OFFICIAL   METHOD    FOR   TOTAL   PHOSPHORIC    ACID  59 

calcium  phosphate  from  the  weight  of  pyrophosphate  are  given  be- 
low on  the  two  bases,  viz.,  hydrogen  equals  i,  and  oxygen 
equals  16. 

H=i. 

Mg2P207Xo.63756=P205 
Mg2P207Xi.39i8=Ca3(P04)2 
P205X2.i83i=Ca3(P04)2 

O=id 

Mg2P207Xo.63757=P205 
Mg2P207Xi.3932=Ca3(P04)2 
P205X2.i852=Ca3(P04)2 

64.  Official  Method  for  Total  Phosphoric  Acid. — Having  now 
described  the  approved  methods  of  bringing  into  solution  all  the 
phosphorus  in  the  form  of  phosphoric  acid,  the  next  step  is  to 
separate  this  acid  and  bring  it  into  a  homogeneous  compound  in 
which  it  may  be  titrated  or  weighed.  The  usual  method  of 
separation  depends"  on  the  property  possessed  by  phosphoric  acid 
of  forming  in  a  strongly  acid  solution,  which  prevents  the  pre- 
cipitation of  the  associated  bodies,  an  insoluble  compound  with 
molybdic  acid.  The  separation  is  accomplished  as  follows  :29 
Determination. — Neutralize  an  aliquot  portion  of  the  solution 
prepared  as  above,  corresponding  to  0.25  gram,  0.50  gram, 
or  one  gram,  with  ammonia,  and  clear  with  a  few  drops  of  nitric 
acid.  In  case  hydrochloric  or  sulfuric  acid  has  been  used  as 
solvent,  add  about  15  grams  of  dry  ammonium  nitrate  or  a  solu- 
tion containing  that  amount.  To  the  hot  solution  add  50  cubic 
centimeters  of  molybdic  solution  for  every  decigram  of  P2O3 
that  is  present.  Digest  at  about  65°  for  an  hour,  filter,  and  wash 
with  cold  water,  or  preferably  ammonium  nitrate  solution.  Test 
the  filtrate  for  phosphoric  acid  by  renewed  digestion  and  addition 
of  more  molybdic  solution.  Dissolve  the  precipitate  on  the  filter 
with  ammonia  and  hot  water  and  wash  into  a  beaker  to  a  bulk 
of  not  more  than  100  cubic  centimeters.  Nearly  neutralize  with 
hydrochloric  acid,  cool,  and  add  magnesia  mixture  from  a  bur- 
ette; add  slowly  (about  one  drop  per  second),  stirring  vigorously. 
After  15  minutes  add  12  cubic  centimeters  of  ammonia  solu- 
29  Bureau  of  Chemistry,  Bulletin  107,  1907  :  3. 


60  AGRICULTURAL   ANALYSIS 

tion  of  density  0.90.  Let  stand  for  some  time ;  two  hours  is  usual- 
ly enough.  Filter,  wash  with  2.5  per  cent.  NH3  until  practically 
free  from  chlorids,  ignite  to  whiteness  or  to  a  grayish  white,  and 
weigh. 

65.  Influence  of  Insoluble  Silica. — It  is  assumed  in  the  above 
methods  that  there  is  no  more  than  a  mere  trace  of  soluble  silica 
in  the  solutions  of  the  phosphate  with  which  the  operations  are 
conducted.     Silica  in  solution  (silicic  acid)  has  also  the  property 
of  forming  yellow  compounds  with  molybdate  of  ammonia  and 
thus  when  present  in  any  quantity  would  contaminate  the  precip- 
itate produced.     This  trouble  is  avoided  if  the  acid  solution  of 
the  phosphate  is  evaporated  to  dryness,  rubbed  to  a  fine  powder 
before  becoming  perfectly  dry,  moistened  with  hydrochloric  acid 
and  taken  up  with  water.     The  pasty  state  of  the  phosphoric  acid 
and  large  quantities  of  soluble  salts  present  in  these  cases  make 
this  a  tedious  process  to  be  practiced  only  when  necessary. 

66.  Use  of  Tartaric  Acid  in  Phosphoric  Acid  Estimation. — In 
the  presence  of  iron  the  molybdate  mixture  is  likely  to  carry 
down  some  ferric  oxid  with  the  yellow  precipitate.     To  prevent 
this,  and  also  hinder  the  separation  of  molybdic  acid  in  the  solu- 
tion on  long  standing,  tartaric  acid  has  been  recommended. 

Jiiptner  has  found  that  the  presence  of  tartaric  acid  does  not 
interfere  with  the  separation  of  the  yellow  precipitate,  as  some 
authorities  assert.30  Even  100  grams  of  the  acid  in  one  liter  of 
molybdate  solution  produce  no  disturbing  effect.  Molybdate 
solution  treated  with  tartaric  acid  does  not  show  any  separation 
of  molybdic  acid  when  kept  for  a  year  at  room  temperatures. 
The  presence  of  tartaric  acid,  therefore,  is  highly  useful  in  pre- 
venting the  danger  of  obtaining  both  ferric  oxid  and  molybdic 
acid  with  the  yellow  precipitate. 

67.  Water-Soluble  Phosphoric  Acid. — The  method  of  procedure 
recommended  by  the  Association  of  Official  Agricultural  Chemists 
is  as  follows:31     Place  two  grams  of  the  sample  in  a  nine  centi- 
meter filter ;  wash  with  successive  small  portions  of  cold  water,  al- 
lowing   each    portion    to    pass    through    before    adding    more, 

30  Chemisches  Central-Blatt,  1894,  2  :  813. 
sl  Bureau  of  Chemistry,  Bulletin  107,  1907  :  3. 


CITRATE-INSOLUBLE    PHOSPHORIC    ACID  6 1 

until  the  filtrate  measures  about  250  cubic  centimeters.  If  the 
filtrate  be  turbid,  add  a  little  nitric  acid.  Make  up  to  any  con- 
venient definite  volume;  mix  well;  take  any  convenient  portion 
and  proceed  as  under  total  phosphoric  acid. 

68.  Citrate-Insoluble  Phosphoric  Acid. — The  official  method  ap- 
plied to  samples  previously  acidulated  is  as  follows:  Heat  100 
•cubic  centimeters  of  strictly  neutral  ammonium  citrate  solution  of 
1.09  specific  gravity  to  65°  in  a  flask  placed  in  a  bath  of  warm 
water,  keeping  the  flask  loosely  stoppered  to  prevent  evaporation. 
When  the  citrate  solution  in  the  flask  has  reached  65°,  drop 
into  it  the  filter  containing  the  washed  residue  from  the  water- 
soluble  phosphoric  acid  determination,  close  tightly  with  a 
smooth  rubber  stopper ;  and  shake  violently  until  the  filter  paper 
is  reduced  to  a  pulp.  Place  the  flask  again  in  the  bath  and 
maintain  the  water  in  the  bath  at  such  a  temperature  that  the 
contents  of  the  flask  will  stand  at  exactly  65°.  Shake  the  flask 
every  five  minutes.  At  the  expiration  of  exactly  30  minutes 
from  the  time  the  filter  and  residue  are  introduced,  remove  the 
flask  from  the  bath  and  immediately  filter  as  rapidly  as  possible. 
It  has  been  shown  by  Sanborn  in  his  investigations,  that 
the  filtration  is  greatly  facilitated  by  adding  asbestos  pulp. 
Wash  thoroughly  with  water  at  65°.  Transfer  the  filter  and  its 
contents  to  a  crucible,  ignite  until  all  organic  matter  is  destroyed, 
add  from  10  to  15  cubic  centimeters  of  strong  hydrochloric 
acid,  and  digest  until  all  phosphate  is  dissolved ;  or  return  the  fil- 
ter with  contents  to  the  digestion  flask,  add  from  30  to  35 
cubic  centimeters  of  strong  nitric,  and  from  five  to  10  cubic 
centimeters  of  strong  hydrochloric  acid,  and  boil  until  all  the  phos- 
phate is  dissolved.  Dilute  the  solution  to  200  cubic  centimeters. 
If  desired,  the  filter  and  its  contents  can  be  treated  according  to 
methods  i,  2,  or  3,  paragraph  61,  under  preliminary  treatment  of 
samples  containing  organic  matter.  Mix  well;  filter  through  a 
dry  filter;  take  a  definite  portion  of  the  filtrate  and  proceed  as 
under  total  phosphoric  acid,  paragraph  64. 

In  case  a  determination  of  citrate-insoluble  phosphoric  acid  be 
required  in  non-acidulated  goods  it  is  to  be  made  by  treating  two 
grams  of  the  phosphatic  material,  without  previous  washing 


62  AGRICULTURAL  ANALYSIS 

with  water,  precisely  in  the  way  above  described,  except  that  in 
case  the  substance  contains  much  animal  matter  (bone,  fish,  etc.), 
the  residue  insoluble  in  ammonium  citrate  is  to  be  treated  by  one 
of  the  processes  described  under  i,  2,  or  3,  paragraph  61. 

69.  Citrate-Soluble  Phosphoric  Acid. — The  sum  of  the  water- 
soluble  and  citrate-insoluble  subtracted  from  the  total  gives  the 
citrate-soluble  phosphoric  acid. 

70.  Time  Required  for  the  Precipitation  of  Phosphoric  Acid. 
—The  length  of  time  required  for  the  complete  precipitation  of 

the  phosphoric  acid  by  molybdate  mixture  is  perhaps  much  less 
than  generally  supposed.  At  65°  the  precipitation,  as  shown  by 
de  Roode,  is  complete  in  five  minutes.32  In  a  given  case  the 
weight  of  pyrophosphate  obtained  after  five  minutes  was  0.0676 
gram,  and  exactly  the  same  weight  was  found  after  24 
hours.  In  view  of  these  facts  analysts  would  often  be  able  to 
save  time  by  omitting  the  delay  usually  demanded  by  the  set- 
ting aside  of  the  yellow  precipitate  for  a  few  hours  in  order  to 
secure  a  complete  separation  of  the  phosphoric  acid.  In  the 
method  of  the  official  chemists  it  is  directed  that  the  digestion  at 
65°  be  continued  for  one  hour,  and  this  time  may  possibly  be 
shortened  with  advantage.  In  all  cases,  however,  where  there 
is  any  doubt  in  regard  to  the  complete  separation,  some  of  the 
molybdate  solution  should  be  added  to  the  filtrate  and,  with 
renewed  digestion,  it  should  be  noted  whether  any  additional 
precipitate  be  formed. 

71.  Examination  of  the  Pyrophosphate. — In  fertilizer  control 
it  is  not  usually  thought  necessary  to  examine  the  magnesium 
pyrophosphate  for  impurities.     Among  those  most  likely  to  be' 
found  is  silica.     It  is  proper,  in  all  cases  where  accuracy  is  re- 
quired, to  dissolve  the  precipitate  in  nitric  acid,  boil  for  some 
time  to  convert  the  pyro-  into  orthophosphate,  and  reprecipitate- 
with  molybdate  and   magnesia  mixture.     This  treatment  will  sep- 
arate the  silica,  which  remains  practically  insoluble  after  the  first 
ignition.     It  has  been  observed  by  some  analysts  that  the  results 
obtained  by  the  official  method  are  a  trifle  too  high  and  also  that 
on  re-solution  the  second  precipitate  of  pyrophosphate  weighs. 

32  Journal  of  the  American  Chemical  Society,  1895,  17  :  43. 


DIRECT   DETERMINATION   OF    PHOSPHORIC   ACID  63 

less  than  the  first.33  The  difference  in  most  cases  is  very  little, 
but  it  may  become  a  quantity  of  considerable  magnitude  in  sam- 
ples where  soluble  silica  is  found  in  notable  quantities.  The  dan- 
ger of  contamination  with  iron,  alumina,  and  arsenic  has  already 
been  mentioned  and  the  precautions  suggested  should  be  careful- 
ly observed. 

72.  Insolubility  of  Silica. — It  is  evident  that  many  of  the  errors 
which  are  incident  to  the  methods  of  separating  phosphoric  acid 
~by  ammonia  phosphomolybdate  are  due  to  the  presence  of  silica. 
The  fact  has  been  repeatedly  pointed  out  by  analysts.     Pellet 
proposes  to  render  the  silica  insoluble  and  thus  prevent  the  error  by 
the  following  procedure  :3*  The  weighed  phosphate  is  placed  in  a 
platinum  capsule  and  moistened  with  free  hydrochloric  acid.     The 
moistened  mass  is  evaporated  to  dryness  after  which  the  silica 
is  no  longer  soluble  in  hot  hydrochloric  acid.     Pellet  claims  that 
this  method,  which  saves  the  time  of  a  previous  solution  and  evap- 
oration to  dryness,  is  quite  as  effective  as  the  longer  method. 

73.  Direct  Determination  of  Available  Phosphoric  Acid. — The 
•direct  determination  of  available  phosphoric  acid  is  not  new,  being 
•official  in  several  of  the  European  countries.     In  this  country, 
however,  it  has  not  met  with  favor,  probably  because  the  citrate 
method  is  not  official  here.     The  necessity  of  destroying  the  or- 
ganic matter  before  precipitating  with  molybdate  solution  pre- 
cludes the  use  of  the  molybdate  method.35 

In  1893  Ross  presented  a  method  for  the  direct  determination 
of  the  reverted  phosphoric  acid.36  While  the  aim  of  this  method 
met  with  hearty  approval  from  the  official  chemists,  the  method 
itself  did  not,  owing  to  some  difficulties  met  with  in  the  manipu- 
lation, and  more  particularly  to  the  fact  that  it  did  not  give 
results  agreeing  with  the  official  method.37  Agreement  could 
hardly  be  expected,  because  the  method  did  not  account  for 
the  phosphoric  acid  removed  in  the  water  used  in  washing  the 
citrate-insoluble.  The  estimation  of  the  available  phosphoric  acid 

33  Journal  of  the  American  Chemical  Society,  1895,  17  =43- 

34  Annales  de  Chitnie  analytique,  1906,  11  :33i. 

35  Veitch,  Journal  of  the  American  Chemical  Society,  1899,  21  :  1090. 

36  Division  of  Chemistry,  Bulletin,  38,  1893  :  17. 

37  Division  of  Chemistry,  Bulletin  43,  1894  :  72  and  Bulletin  47,  1896:  81. 


64  AGRICULTURAL  ANALYSIS 

consisted  in  the  determination  of  the  water-soluble  phosphoric  acid 
by  the  volumetric  method,  as  modified  and  carried  out  by  Veitch  ;3S 
the  direct  determination  of  the  citrate-soluble  by  the  citrate  method 
in  50  cubic  centimeters  of  the  citrate  filtrate,  and  the  determina- 
tion of  that  removed  by  washing  the  citrate-insoluble  residue,, 
using  the  modified  volumetric  method.  The  sum  of  these  three 
results  should  equal  the  available  phosphoric  acid  by  the  official 
method. 

It  is  perhaps  sufficient  to  say  that  the  citrate  method  at  that 
time  and  later  gave  satisfactory  results.39 

The  two  methods  gave  practically  the  same  results  on  availables 
and  on  totals.  The  work  also  shows  very  plainly  why  the  Ros& 
method  differs  from  the  official,  from  0.09  per  cent,  to  1.48  per 
cent,  being  removed  and  accounted  for  in  the  wash  water  of  the 
official  method  that  could  not  be  accounted  for  by  the  Ross  method. 
Of  course,  the  amount  removed  by  the  wash  water  will  vary 
somewhat  in  the  hands  of  different  analysts,  according  as  they 
wash  the  citrate-insoluble  much  or  little.  It  is  the  practice  of 
Veitch  to  wash  until  the  filtrate  and  washings  amount  to  about 
250  cubic  centimeters. 

A  comparison  of  the  official  method  with  the  citrate  and  the 
molybdate  methods,  precipitating  with  magnesia  mixture  and  with 
molybdate  solution,  respectively,  in  the  mixed  filtrates  con- 
taining  the  water-soluble  and  the  citrate-soluble,  was  undertaken. 

The  method  finally  adopted  is  as  follows:  The  water-soluble 
extracted  as  usual,  is  received  in  a  500  cubic  centimeter  flask, 
graduated  roughly  at  250  cubic  centimeters  and  containing  from 
five  to  10  cubic  centimeters  nitric  acid.  The  citrate-soluble  is  then 
extracted  as  usual  and  the  filtrate  and  washings  received  in  the 
flask"  with  the  water-soluble.  After  cooling,  the  volume  is  com- 
pleted, shaken,  filtered,  and  in  aliquots  of  100  cubic  centimeters 
the  phosphoric  acid  is  determined  by  one  of  two  methods,  the 
molybdate  or  citrate,  the  precipitants  being  added  directly  to  the 
solution  without  destroying  the  organic  matter,  and  the  precipi- 

38  Journal  of  the  American  Chemical  Society,  1896,  1 8  :  389. 
w  Division  of  Chemistry,  Bulletin  49,  1897  :  61. 


DIRECT    DETERMINATION   OF   PHOSPHORIC    ACID  65 

tates  are  allowed  to  stand  over  night  before  filtering.  The  de- 
terminations are  completed  as  usual. 

The  results  by  the  citrate  method  were  unexpectedly  low.  In 
Veitch's  hands  this  method  has  always  given  satisfactory  results, 
even  on  low  percentages.  It  is  probable  the  low  results  are  due 
to  an  excess  of  citrate.  This  addition  is  unnecessary,  and  bet- 
ter results  obtained  when  more  citrate  is  not  added,  lead  to  the 
belief  that  this  additional  citrate  is  the  cause  of  the  low  results. 

The  results  by  the  molybdate  method  are  good.  It  was  feared 
that  the  organic  matter  present  would  prevent  the  complete  pre- 
cipitation of  the  ammonium  phosphomolybdate.  To  insure  com- 
plete precipitation  the  samples  were  allowed  to  stand  over  night 
before  filtering. 

Notwithstanding  the  oft-repeated  statement  that  salts  of  or- 
ganic acids  and  organic  matter  generally  prevent  the  complete  pre- 
cipitation of  ammonium  phosphomolybdate,  the  molybdate  method 
is  used  to  determine  soluble  phosphoric  acid  in  the  presence  of 
what  organic  matter  may  be  dissolved  by  the  water  used  in  the 
extraction.  In  the  Wagner  method  for  basic  slag,  the  precipi- 
tation is  accomplished  with  molybdate  solution  in  the  presence  of 
three  grams  of  citric  acid.  Lorenz  precipitates  in  the  presence 
of  two  per  cent,  of  citric  acid  to  prevent  contamination  with  mag- 
nesia. Jiiptner  uses  as  much  as  100  grams  of  tartaric  acid  per 
liter  of  molybdate  solution  to  prevent  the  precipitation  of  iron 
and  the  separation  of  molybdic  acid.40  The  successful  use  of  the 
molybdate  method  in  these  cases  seems  to  warrant  the  conclusion 
that  we  are  needlessly  alarmed  at  the  presence  of,  at  least,  some 
forms  of  organic  matter  in  phosphate  solutions. 

The  direct  determination  of  the  available  phosphoric  acid  pos- 
sesses several  advantages.  Only  one  determination  is  required 
instead  of  two  as  by  the  present  method.  The  probable  error  is 
reduced  one-half.  The  soluble,  reverted,  insoluble,  and  total  phos- 
phoric acid  can  also  be  determined  in  one  sample  and  with  one 
weighing,  where  it  now  takes  two  samples  and  two  weighings. 

The  saving  of  time  effected  by  this  method  is  of  considerable 
40  Abstract,  Experiment  Station  Record,  1894-5,  6  :  610. 
3 


66  AGRICULTURAL   ANALYSIS 

importance  in  control  and  in  factory  laboratories,  whether  the 
citrate  or  the  molybdate  method  is  used. 

74.  International  Methods. — The  international  commission  for 
the  analysis  of  artificial  fertilizers  presented  a  report  to  the  Fifth 
International  Congress  of  Applied  Chemistry  embracing  certain 
processes  of  analysis  which  are  recommended  for  international 
adoption.41  The  methods  suggested  for  phosphoric  acid  are  as 
follows : 

1.  Determination   of  Moisture. — Ten  grams  of  the  substance 
are  used ;  the  drying  is  conducted  at  100°  to  constant  weight ;  sub- 
stances containing  gypsum  are  dried  three  hours. 

For  potash  salts  the  regulations  of  the  Kali  syndicate  at  Leo- 
poldshall-Stassfurt  hold  good. 

2.  Determination    of   Insoluble   Matter. — Ten   grams    of   the 
substance  are  used. 

A.  When  the  substance  is  dissolved  in  mineral  acids,  the  silica 
is  rendered  insoluble  and  the  total  residue  ignited. 

B.  When  the  substance  is  dissolved  in  water,  the  residue  is  dried 
at  1 00°  to  constant  weight. 

3.  Determination  of  Phosphoric  Acid. — A.     Method  of  mak- 
ing the  solutions. 

1.  In   the   case   of   water-soluble    P2O5,    20   grams   substance 
are  to  be  agitated  for  30  minutes  with  about  800  cubic  centimeters 
water  in  a  liter  bottle  and  then  filled  up  to  1000  cubic  centimeters. 
The  solution  of  so-called  double  superphosphates  must  be  boiled 
with  HXO3  previous  to  precipitation  of  the  P2O5,  whereby  any 
pyrophosphoric  acid   which   may  be   present   is   converted   into 
orthophosphoric  acid. 

For  every  25  cubic  centimeters  of  solution  of  double  superphos- 
phate, 10  cubic  centimeters  concentrated  HNO3  must  be  used. 

When  the  amount  of  citrate-soluble  phosphoric  acid  in  super- 
phosphates is  required,  the  determination  must  be  made  accord- 
ing to  Petermann. 

2.  For  total  phosphoric  acid  five  grams  of  the  substance  are 
boiled  with  aqua  regia  or  20  cubic  centimeters  HNO3  and  50 

41  Proceedings  of  the  Fifth  International  Congress  of  Applied  Chemistry, 
Berlin,  1903,  1  1228. 


INTERNATIONAL,  METHODS  67 

grams  concentrated  H2SO4  for  30  minutes  and  filled  up  to  500 
cubic  centimeters. 

3.  To  determine  P2O5  in  slag  phosphates,  the  meal,  which  ap- 
pears to  contain  coarse  particles,  is  passed  through  a  two 
millimeter  sieve;  the  portion  which  remains  behind  is  slightly 
crushed.  The  determination  of  P2O5  is  made  in  the  portion  which 
passes  through  the  sieve,  the  result  being  calculated  so  as  to  in- 
clude the  portion  which  remains  behind. 

(a)  Citric  acid  soluble  P2O5. 

Five  grams  of  the  substance  are  placed  in  a  500  cubic  centi- 
meter flask  with  five  cubic  centimeters  of  alcohol  to  prevent  bak- 
ing and  shaken  with  two  per  cent,  citric  acid  solution  for  one  half 
hour  at  17°. 5  in  a  rotary  apparatus  which  makes  30-40  revolutions 
per  minute. 

(b)  Total  P2O5.42 

Ten  grams  of  the  substance  are  placed  in  a  500  cubic  centi- 
meter flask,  thoroughly  mixed  with  a  few  cubic  centimeters  of 
water  and  boiled  for  30  minutes  with  50  cubic  centimeters  concen- 
trated H2SO4,  the  flask  being  frequently  shaken. 

B.  Analysis  of  the  Solutions. 

i.  Molybdate  method  according  to  Fresenius  and  P.  Wagner. 

2..  Citrate  method. 

3.  Free  acid. 

(a)  Total  free  acid:     The  aqueous  solution  A   I   is  titrated 
with  a  solution  of  NaOH,  using  methyl  orange  as  an  indicator. 

(b)  Free  phosphoric  acid:     An  alcoholic  solution  is  used  for 
making  a  gravimetric  determination. 

4.  Determination  of  Ferric  Oxid  and  Alumina. 

This  determination  must  be  made  either  according  to  the  meth- 
od of  Eugen  Glaser43  as  improved  by  R.  Jones44  or,  in  the  case 
of  the  determination  of  alumina,  according  to  Henri  Lasne.45  The 
method  adopted  must  be  mentioned. 

42  When  a  determination  of  the  fine  dust  is  to  be  made,  a  sieve  of  0.17 
millimeter  mesh  must  be  used. 

43  Zeitschrift   fur   angewandte     Chemie,    1889,    2  :  636 ;  Die    landwirt- 
schaftlichen  Versuchs-Stationen,  1891,  38  :  284. 

44  Zeitschrift  fur  angewandte  Chemie,  1891,  4  :  3;  Zeitschrift  fur  analyt- 
ische  Chemie,  1891,  30  :  743. 

"Bulletin   de  la  Socie'te'   chimique  de  Paris,  1896,    [3],    15  :  146,  23?; 
Chemiker-Zeitung  Repertorium,  1896,  20  :  47,  65. 


68  AGRICULTURAL   ANALYSIS 

75.  Methods  of  the   German  Experiment  Stations. — The  pro- 
cesses adopted  by  the  union  of  the  German  agricultural  experi- 
ment stations  are  based  on  the  general  methods  of  procedure 
already  outlined  as  is  seen  from  the  following  resume.48     The 
sample  containing  the  phosphoric  acid  is  dissolved  in  aqua  regia 
in  the  proportion  of  five  grams  of  the  sample  to  50  cubic  centi- 
meters of  the  acid,  made  by  mixing  three  parts  of  hydrochloric 
acid  of    1. 1 2  specific  gravity  with  one  part  of  nitric  acid  of 
1.25  specific  gravity  or  20  cubic  centimeters  of  nitric  acid  of  1.42 
specific  gravity   with    50    cubic    centimeters    of    sulfuric    acid 
of  1.8  specific  gravity.     With  the  latter  reagent  the  boiling  is  con- 
tinued for  30  minutes.     The  phosphoric  acid  is  then  determined 
by  the  direct  (Bottcher)   method.47 

76.  Water-Soluble  Phosphoric  Acid. — The  soluble  acid  in  acid 
phosphates  is  extracted  by  treating  20  grams  of  the  sample  in  a 
liter  flask  with  800  cubic  centimeters  of  water  for  30  minutes  with 
vigorous  shaking,  filling  the  flask  to  the  mark,  shaking  and  filling. 
A  mechanical  shaker  is  recommended  with  a  vibration  or  rotation 
of  150  turns  a  minute.    The  acid  is  determined  in  an  aliquot  part 
of  the  filtrate  by  the  magnesia  citrate  method.  Solutions  of  double 
acid  phosphates  are  boiled  with  nitric  acid  before  treatment  in 
order  to  bring  all  the  phosphoric  acid  in  the  ortho  form.     When 
required  the   content  in   water-soluble   and   citrate-soluble   acid 
must  be  returned  separately  and  not  in  one  figure  as  citrate-solu- 
ble acid.     It  was  decided  that  the  new  Wagner  method  for  de- 
termining citrate-soluble  acid  in  basic  slag  should  be  adopted. 
This  method  is  given  in  another  paragraph,  and  it  is  not  to  be 
applied  to  other  phosphatic  materials  such  as  bone-meal. 

77.  Official  Norwegian  Methods. — The  Director  of  the  Chemical 
Control  Station  of  Norway,  expresses  the  opinion,  that  for  Nor- 
wegian, Swedish,  Danish  and  German  conditions,  the  quantities 
of  material  required  by  the  American  methods  for  the  determina- 
tion of  phosphoric  acid,  notwithstanding  their  analytical  exact- 

46  Die  landwirtschaftlichen  Versuchs-Stationen,  1904,  60  :  371. 

47  Die  landwirtschaftlichen  Versuchs-Stationen,   1903-4,   59:313;  1904, 
60  :  221. 


METHODS    FOR    PHOSPHORIC    ACID   USED    IN   NORWAY          69 

ness,  are  insufficient.48  In  those  countries  are  found  many,  in  part, 
poorly  pulverized,  and  badly  mixed  manures,  such  as  ammonium- 
superphosphate,  potassium-superphosphate,  and  potassium-ammo- 
nium-superphosphate, and  these  can  not  usually  be  so  well  pul- 
verized and  mixed  that  one  can  secure  a  true  average  sample  of 
from  two  to  two  and  five-tenths  grams.  Care  in  the  analysis  is  use  - 
less  when  the  material  employed  does  not  represent  the  average 
conditions  of  the  materials  investigated.  Therefore,  in  the  coun- 
tries named,  often  from  10  to  20  grams,  and  almost  never  less 
than  five  grams  of  substance  are  used  in  the  preparation  of  the 
solutions,  except,  for  instance,  in  the  determination  of  nitrogen 
and  reverted  phosphoric  acid. 

78.  Methods  for  Phosphoric  Acid  Used  in  the  Norway  Stations.40 
• — i.  Description  of  the  Method  for  Total  Phosphoric  Acid. — For 
determining  the  phosphoric  acid  in  bone-meal,  fish-guano,  and 
superphosphates,  five  grams  of  the  substance,  with  20  cubic 
centimeters  of  nitric  acid  of  1.42  specific  gravity,  and  50  cubic 
centimeters  of  sulfuric  acid  of  1.8  specific  gravity,  are  boiled  half 
an  hour  in  a  half  liter  flask,  diluted  with  water,  and  after  cool- 
ing, made  up  to  the  mark.  Fifty  cubic  centimeters  of  the  filtrate 
are  made  alkaline  with  ammonia,  then  acid  with  nitric  acid,  pre- 
cipitated with  50  cubic  centimeters  of  molybdic  solution  for  every 
one-tenth  gram  of  phosphorus  pentoxid  present,  heated  over 
the  water  bath  for  one  hour,  and  allowed  to  stand  12  hours, 
when  the  supernatant  liquid  is  separated  by  decantation,  the  pre- 
cipitate washed  thoroughly  with  dilute  molybdate  solution  (1:4), 
dissolved  in  warm  dilute  ammonia,  and  the  filter  washed  with  hot 
water.  The  ammoniacal  solution  is  neutralized  with  hydrochloric 
acid,  cooled,  mixed,  drop  by  drop,  with  constant  stirring,  with 
from  10  to  20  cubic  centimeters  of  magnesia  mixture,  and 
after  a  quarter  of  an  hour  one-third  the  volume  of  10  per  cent, 
ammonia  is  added.  This,  after  standing  two  hours,  is  filtered, 
washed  with  five  per  cent,  ammonia  until  the  disappearance  of 
Ihe  chlorin  reaction,  dried,  burned  in  an  open  crucible  over  a 
bunsen,  and  finally,  for  a  quarter  of  an  hour,  in  a  covered  cru- 
cible over  the  blast. 

48  Division  of  Chemistry,  Bulletin  47,  1896  :  85. 

49  Solberg,  Division  of  Chemistry,  Bulletin  47,  1896  :  83. 


70  AGRICULTURAL   ANALYSIS 

2.  Water-Soluble  Phosphoric  Acid. — To    20      grams    of    the 
substance  in  a  liter  flask,  are  added  800  cubic  centimeters  of  water, 
shaken  every   15  minutes  for  two  hours;  the  volume  is  made 
up  to  the  mark  and  the  phosphoric  acid  in  50  cubic  centimeters 
of  the  filtrate,  equalling  one  gram  substance,  is  determined  as  un- 
der total. 

3.  Reverted  Citrate-Soluble  Phosphoric  Acid. — Two  and  five- 
tenths  grams  substance  are  rubbed  up  with  water,  washed  upon 
the  filter  with  about  100  cubic  centimeters  of  water,  the  residue 
on  the  filter  washed  into  a  flask  with  a  part  of  the  measured  cit- 
rate solution,  and  digested  one  hour  at  from  35°  to  40°  with  200 
cubic  centimeters  of  Petermann's  citrate  solution.     The  water  and 
citrate  extracts  are  made  up  to  a  quarter  of  a  liter  each,  and 
the  phosphoric  acid  determined  in  from  25  to  50  cubic  centime- 
ters, according  to  the  quantity  present. 

Solutions,  i.  Molybdate  Solution. — Three  hundred  and  seven- 
ty-five grams  of  ammonium  molybdate  are  dissolved  in  two  and 
five-tenths  liters  of  water,  and  the  solution  poured  into  two  and 
five-tenths  liters  of  nitric  acid  of  1.20  specific  gravity. 

2.  Magnesia  Mixture. — Two  hundred  and  seventy-five  grams 
of  crystallized  magnesium  chlorid  and  350  grams  of  ammonium 
chlorid  are  dissolved  in  3250  cubic  centimeters  of  water  and  filled 
up  to  five  liters  with  ammonia  of  0.96  specific  gravity. 

3.  Petermann's  Solution. — One  kilogram  of  citric  acid  is  dis- 
solved in  about  two  liters  of  water  and  1350  cubic  centimeters  of 
ammonia  of  0.925  specific  gravity  and  filled  up  with  water  to 
5750  cubic  centimeters.     The  solution  then  has  a  specific  gravity 
of  1.09;  300  cubic  centimeters  of  ammonia  of  0.925  specific  grav- 
ity are  added. 

79.  The  Molybdic  Acid  Method  as  Practiced  by  Members 
of  the  Union  of  the  German  Experiment  Stations. — The  method 
adopted  by  the  German  experiment  stations  is  essentially  that 
used  at  Halle.50  The  samples  are  brought  into  solution  in  the 
following  way:  For  the  estimation  of  phosphoric  acid  in  bone- 
meal,  fish-guano,  flesh  preparations  and  raw  phosphates,  and  the 
total  phosphoric  acid  in  superphosphates,  five  grams  of  the  sample 
50  Die  landwirtschaftlichen  Versuchs-Stationen,  1891,  38  :  306. 


THE   MOLYBDIC    ACID   METHOD  Jl 

are  dissolved  in  50  cubic  centimeters  of  aqua  regia,  made  of  three 
parts  of  hydrochloric  acid  of  1.12  specific  gravity  and  one  part 
of  nitric  acid  of  1.25  specific  gravity,  or  the  solvent  may  be  made 
of  a  mixture  of  20  cubic  centimeters  of  nitric  acid  of  1.42 
specific  gravity  and  50  cubic  centimeters  of  sulfuric  acid  of  1.8 
specific  gravity.  The  boiling  should  continue  for  half  an  hour. 
The  solution  is  made  up  to  half  a  liter  and  filtered.  Fifty  cubic 
centimeters  of  the  filtrate  containing  the  phosphoric  acid,  (with 
double  superphosphates,  25  cubic  centimeters),  are  digested  with 
200  cubic  centimeters,  of  ammonium  molybdate  solution  for 
three  hours  at  50°  in  a  water  bath  and,  after  cooling,  filtered,  so 
that  as  little  as  possible  of  the  precipitate  is  collected  upon  the 
filter,  which  is  made  of  strong  paper. 

The  yellow  precipitate  is  washed  by  decantation  in  the  flask 
nine  times  with  20  cubic  centimeters  of  molybdic  solution 
diluted  with  one  volume  of  water  and  the  filter  washed  out  once 
with  the  same  quantity  of  liquid.  The  funnel,  with  the  filter,  is 
immediately  placed  upon  the  flask  and  the  portion  of  the  precipi- 
tate collected  in  the  filter  dissolved  in  five  per  cent,  ammonia, 
which  is  easily  accomplished  by  throwing  ammonia  upon  it  from 
a  wash  bottle.  Afterwards  the  filter  is  washed  with  a  sufficient 
quantity  of  hot  water  and  finally  removed.  The  contents  of  the 
flask  are  neutralized  while  warm  with  hydrochloric  acid,  the  acid 
being  added  until  the  precipitate  first  formed,  after  continued  shak- 
ing, is  again  dissolved  in  the  liquid.  The  solution  is  then  cooled 
and  treated,  drop  by  drop,  with  constant  stirring,  with  20  cubic 
centimeters  of  magnesia  mixture.  Finally  25  cubic  centimeters  of 
dilute  ammonia  solution  are  added,  the  precipitate  is  not  shaken, 
and  after  two  hours  is  filtered  through  a  gooch. 

For  the  filtering  of  the  ammonium  magnesium  phosphate  by 
the  molybdic  method,  freshly  prepared  felts  are  always  employed 
since  the  remarkably  fine  crystalline  precipitates  will  pass  through 
a  filter  which  has  once  been  used.  It  is  necessary  also  that 
special  precautions  be  taken  in  the  ignition.  The  crucible 
should  be  heated  in  a  platinum  cap,  Vhich  has  the  purpose  of 
protecting  the  contents  of  the  crucible  from  the  access  of  redu- 
cing gases  during  the  ignition.  After  redness  has  been  reached 


72  AGRICULTURAL   ANALYSIS 

the  cap  can  be  removed  and  the  crucible  transferred  to  a  blast 
where  it  is  strongly  ignited  for  10  minutes  before  weighing. 
The  precipitate  should  be  pure  white. 

The  molybdic  solution  is  prepared  as  follows :  One  hundred 
and  fifty  grams  of  ammonium  molybdate  are  dissolved  in  a  liter 
of  water,  and  after  the  solution  is  completely  cooled,  poured  into 
a  liter  of  nitric  acid  of  1.2  specific  gravity. 

80.  Estimation  of  Soluble  Phosphoric  Acid. — i.  The  extraction 
of  the  superphosphates  is  made  as  follows :     Twenty  grams  of 
the  superphosphates  are  placed  in  a  liter  flask  with  800  cubic  centi- 
meters of  water  and  shaken  continuously  for  30  minutes.     The 
flask  is  then  filled  with  water  to  the  mark  and  the  whole  again 
thoroughly  shaken  and  filtered.     For  shaking,  a  machine  is  re- 
commended, driven  by  hand  or  water  power.     The  normal  rate 
of  the  machine  is  fixed  at  150  turns  per  minute. 

2.  The  solution  of  double  superphosphates,  obtained  as  above, 
must  be  boiled  with  nitric  acid  before  the  precipitation  of  the  phos- 
phoric acid  in  order  to  convert  any  phosphoric  acid  present  as 
pyrophosphoric  into  tribasic  phosphoric  acid.     For  each  25  cubic 
centimeters  of  the  superphosphate  solution  10  cubic  centimeters  of 
concentrated  nitric  acid  are  added  and  the  mixture  boiled. 

3.  The  precipitation  of  the  phosphoric  acid  is  conducted  by 
the  molybdate  method  as  usually  practiced. 

4.  For  the  estimation  of  iron  and  alumina  in  each  of  the  su- 
perphosphates the  Glaser  alcohol  method  is  recommended  pro- 
visionally.    A  description  of  this  method  is  given  further  on. 

81.  The  French  Official  Method. — For  the  purpose  of  securing 
the  most  appropriate  method  of  analysis  the  materials  to  be  ex- 
amined are  divided  by  the  French  authorities  into  the  following 
classes  rS1 

These  groups  are : 

1.  Mineral    phosphates,    consisting    of    tricalcium  phosphate 
more  or  less  mixed  with  carbonate  of  lime,  silicious  matters,  oxids 
of  iron  and  alumina,  etc. 

2.  Bone  phosphates  an'd  bone  black. 

3.  Phosphates  in  manures,  poudrettes  and  guanos. 

51  Sidersky,  Analyse  des  Engrais,    1901  :  54 ;    L,a  Sucrerie  indigene  et 
coloniale,  1897,  50  :  382. 


THE  FRENCH  OFFICIAL  METHOD  73 

4.  Superphosphates,   precipitated    (reverted)    phosphates,   am- 
monia-magnesium phosphates. 

5.  Phosphatic  slags. 

In  the  first  class  the  phosphoric  acid  is  determined  by  direct 
precipitation  by  the  citrate  method. 

In  the  second  and  third  classes  previous  to  the  separation  of  the 
phosphoric  acid  the  organic  matter  is  destroyed  after  treating 
with  some  slaked  lime  to  prevent  the  organic  matter  from  reduc- 
ing any  phosphate.  After  the  reduction  of  the  organic  matter 
the  process  is  continued  as  in  the  first  class. 

In  the  fourth  class  the  precipitated  (reverted)  phosphoric  acid 
is  dissolved  in  ammonium  citrate.  About  0.75  gram  of  the  sample 
is  rubbed  in  a  mortar  with  a  few  drops  of  the  citrate  solution 
and  the  paste  washed  into  a  flask  of  150  cubic  centimeters  capac- 
ity with  60  cubic  centimeters  of  the  citrate  of  ammonia  solution 
and  digested  with  frequent  shaking  for  12  hours.  The  flask  is 
subsequently  filled  to  the  mark  and,  after  shaking,  the  contents 
are  poured  on  a  filter,  and  in  100  cubic  centimeters  of  the  filtrate, 
representing  0.5  gram  of  the  sample,  the  phosphoric  acid  is  sepa- 
rated as  above. 

The  total   phosphoric   acid   is   determined   as  in  the   first  in 
stance. 

In  the  fifth  class  the  phosphoric  acid  is  separated  as  usual 
after  solution  in  hydrochloric  acid  and  not  nitric.  When  the 
slags  are  very  rich  in  lime  it  is  advisable  to  dissolve  first  in  acetic 
acid  and  separate  the  greater  part  of  the  lime  as  oxalate  before 
dissolving  the  phosphoric  portion  of  the  slag  in  hydrochloric  acid. 

The  molybdate  method  is  also  used  officially  by  the  French 
chemists  in  harmony  with  the  usual  directions. 

The  methods  employed  are  so  nearly  like  those  already  described 
that  their  repetition  is  not  deemed  necessary.  The  determination 
of  the  degree  of  fineness  of  the  sample  is  properly  regarded  by 
the  French  chemists  as  of  great  importance. 

In  the  case  of  natural  phosphates  and  slags  it  is  advised  that 
the  sample  be  separated  by  a  sieve  of  0.17  millimeter  mesh.  At 
least  90  per  cent,  of  the  sample  should  pass  such  a  sieve. 


74  AGRICULTURAL   ANALYSIS 

82.  Swedish  Official  Method  for  Determination  of  Phosphoric 
Acid.52 — The  Swedish  chemists  determine  phosphoric  acid  in  fer- 
tilizers both  by  the  molybdate  and  the  citrate  methods.  These 
methods  carefully  conducted  according  to  the  directions  given 
below,  give  very  concordant  results.  In  doubtful  cases  the  former 
method  is  taken  as  the  deciding  one,  it  having  proved  by  long 
practice  to  give  very  satisfactory  results. 

Reagents  for  the  Molybdate  Method. — i.  Molybdic  Solution. — 
Prepared  by  dissolving  100  grams  of  finely  powdered  molybdic 
acid  with  heat  in  400  grams  of  eight  per  cent,  ammonia  of  0.967 
specific  gravity  and  pouring  the  solution  into  1500  grams  of  nitric 
acid  of  one  and  two-tenths  specific  gravity ;  or  else  by  dissolv- 
ing 150  grams  ammonium  molybdate  in  one  liter  of  hot  water,  and 
pouring  the  solution  into  one  liter  of  nitric  acid  of  1.2  specific 
gravity.  Prepared  in  this  way,  the  molybdic  solution  will  con- 
tain, in  the  former  case,  five  per  cent.,  in  the  latter  case,  from  five 
to  six  per  cent,  of  molybdic  acid,  and  100  cubic  centimeters  of  it 
are  required  for  precipitating  one-tenth  gram  of  phosphorus 
pentoxid. 

2.  Magnesia  Mixture. — Prepared  with  no  grams  of  crystal- 
lized magnesium  chlorid,  140  grams  of  ammonium  chlorid,  700 
grams  of  eight  per  cent,  ammonia  of  0.967  specific  gravity  and 
1300  grams  of  distilled  water.  The  mixture  is  filtered  after  a  few 
days,  if  necessary ;  10  cubic  centimeters  are  required  for  precipi- 
tating one-tenth  gram  of  phosphorus  pentoxid. 

3.  Ten  per  cent,  ammonia  of  0.959  specific  gravity. 

Determinations:  (a)  Water-Soluble  Phosphoric  Acid. — i. 
Preparation  of  the  Aqueous  Solution. — Of  superphosphates  and 
other  fertilizers  containing  water-soluble  phosphoric  acid,  20 
grams  are  treated  with  water  in  a  mortar ;  lumps  are  crushed 
lightly  but  completely  with  the  pestle  without  pulverizing 
finer;  the  whole  mass  is  then  washed  into  a  graduated  flask  hold- 
ing one  liter,  which  at  once  is  filled  up  to  the  mark.  The  volume 
taken  up  by  the  residue  insoluble  in  water  is  left  out  of  considera- 
tion in  the  calculation.  After  standing  in  the  flask  (  which  is 

51  Official  Swedish  Methods  Translated  for  the  Author  by  F.  W.  Woll. 


SWEDISH    DETERMINATION   OF   PHOSPHORIC   ACID  75 

* 

occasionally  shaken)  at  the  ordinary  temperature  of  the  room  for 
two  hours,  the  mixture  is  filtered. 

2.  The  Determination. — To  25  cubic  centimeters  of  the  super- 
phosphate solution  thus  prepared  (or  a  quantity  of  the 
sample  equal  to  one-tenth  gram  phosphorus  pentoxid)  add  a 
quantity  of  molybdic  solution  sufficient  for  complete  precipitation, 
leave  standing  for  four  hours  in  a  beaker  covered  with  a  watch- 
glass;  decant  the  solution  through  a  small  filter,  wash  the  pre- 
cipitate first  by  decantation,  then  on  the  filter,  with  a  mixture  con- 
taining 100  parts  fnolybdic  solution,  20  parts  nitric  acid  of 
1.2  specific  gravity,  and  80  parts  water,  until  a  few  drops 
put  into  alcohol,  to  which  some  dilute  sulfuric  acid  has  been  added, 
do  not  any  longer  cause  turbidity.  The  molybdic  precipitate  is 
now  washed  with  a  little  water  from  the  filter  into  a  beaker 
and  particles  adhering  to  the  filter  are  dissolved  by  a  hot  mix- 
ture of  one  part  ammonia  and  three  parts  water,  which  is  allowed 
to  flow  into  the  beaker  till  the  precipitate  is  finally  completely 
dissolved  in  it.  To  the  clear  solution  add  dilute  hydrochloric  acid 
while  stirring  till  the  yellow  precipitate  formed  by  the  acid  is  no 
longer  immediately  dissolved;  then  add  from  six  to  eight  cubic 
centimeters  of  ammonia  through  the  filter.  The  volume  of  the 
solution  is  not  to  exceed  75  cubic  centimeters.  It  is  cooled  com- 
pletely and  one  cubic  centimeter  of  magnesia  mixture  is  added 
from  a  burette  for  every  centigram  of  phosphorus  pentoxid 
which  it  is  expected  to  contain,  and  finally  one-quarter*  of 
its  volume  of  ammonia  is  added.  The  precipitate  may  be  filtered 
after  four  hours,  and  washed  on  the  filter,  preferably  by  means  of 
suction,  with  a  mixture  of  one  part  ammonia  and  three  parts 
water  till  the  filtrate  is  entirely  free  from  chlorin.  After  drying, 
heat  the  precipitate,  first  gently,  then  stronger,  and  finally  with  a 
blast  for  a  few  minutes  and  then  weigh  it. 

Treated  with  hydrochloric  acid  it  must  leave  no  insoluble  residue 
(SiO2),  nor  should  hydrogen  sulfid  cause  any  precipitation  in  the 
solution  thus  formed  (MoO3). 

(b)  Total  Phosphoric  Acid. — i.  In  Superphosphates. — For  the 
determination  of  total  phosphoric  acid,  treat  a  weighed  quantity 
of  the  superphosphate  with  nitric  acid,  if  necessary  to  bring  a  dif- 


76  AGRICULTURAL   ANALYSIS 

*• 

ficultly  soluble  residue  into  solution,  with  addition  of  hydrochloric 
acid,  or  of  potassium  chlorate,  to  destroy  organic  matter  present. 
Dilute  the  solution  to  a  definite  volume  and  determine  the  phos- 
phoric acid  in  a  measured  quantity  thereof,  as  directed  under  (a) 
2;  if  hydrochloric  acid  or  potassium  chlorate  be  applied  in  the 
preparation  of  the  solution,  however,  the  determination  of  the 
phosphoric  acid  must  not  be  made  till  the  measured  quantity 
has  been  repeatedly  evaporated  to  dryness  with  concentrated  nitric 
acid. 

2.  In  Bone-meal. — Destroy  organic  matter  in  five  grams  of  the 
sample  by  ignition,  dissolve  the  residue  in  nitric  acid,  filter  from 
the  insoluble  residue,  dilute  the  filtrate  to  half  a  liter,  and  deter- 
mine the  phosphoric  acid  as  directed  under  (a)  2  in  an  aliquot 
part  containing  about  one-tenth  gram  phosphoric  pentoxid. 

3.  In  Fish-guano   (and  other  fertilizing  materials  of  organic 
origin). — The  organic  matter  cannot  here  be  removed  by  sim- 
ple ignition,  as  in  this  way  a  loss  of  phosphorus  may  take  place ; 
it  is  therefore  destroyed  either  in  the  wet  way  by  nitric  acid  and 
potassium  chlorate,  or  in  the  dry  way  by  fusion  with  a  mixture  of 
potassium  nitrate  and  sodium  carbonate,  otherwise  the  procedure 
is  as  in  (b)   I. 

4.  In  Mineral  Phosphates. — Determine  the  phosphoric  acid  in 
a  solution  obtained  by  nitric  acid ;  organic  matter  if  present  is 
destroyed  preferably  in  the  wet  way. 

5.  In  Basic  Slag. — Dissolve   10  grams  of  powdered  slag  by 
treating  it  with  100  cubic  centimeters  of  hot  fuming  hydrochloric 
acid;  wash  the  solution  into  a  graduated  half  liter  flask,  fill  to 
the  mark,  shake  well,  and  filter.     Determine  the  phosphoric  acid 
in  25  cubic  centimeters  of  the  clear  filtrate,  according  to  (a)  2, 
after  having  first,  however,  evaporated  the  solution  to  dryness 
and  then  at  least  three  times  evaporated  the  residue  to  dryness 
with  concentrated  nitric  acid. 

83.  Method  Employed  by  the  Royal  Experiment  Station  of  Hol- 
land.— A.  Soluble  Phosphoric  Acid.™ — The  necessary  reagents 
are: 

(i)  Molybdate  solution,  made  by  dissolving  150  grams  of  am- 

M  Methoden  van  Onderzoek  aan  de  Rijkslandbouwproefstations,  1893  :  4. 


METHOD  EMPLOYED  BY  HOLLAND  77 

monium  molybdate  in  a  liter  of  water  and  pouring  the  solution 
into  a  liter  of  nitric  acid  of  1.20  specific  gravity. 

(2)  A  10  per  cent,  solution  of  ammonium  nitrate. 

(3)  Strong  and  dilute  ammonia,  the  latter  being  between  two 
and  five-tenths  and  three  per  cent,  and  of  0.988  specific  gravity.. 

(4)  Magnesia  mixture  made  by  dissolving  no  grams  of  crys- 
tallized magnesium  chlorid,  140  grams  of  ammonium  chlorid,  and 
700  cubic  centimeters  of  ammonia  of  •  0.96  specific  gravity  in 
water  and  bringing  the  solution  to  two  liters. 

(5)  Ammoniacal  citrate  solution,  made  by  dissolving  500  grams 
of  citric  acid  in  a  liter  of  water,  and  mixing  with  four  liters  of 
10  per  cent,  ammonia  of  0.96  specific  gravity. 

Manipulation. — Place  20  grams  of  the  substance  in  a  mortar 
together  with  some  cold  distilled  water  or  pure  rain  water,  stir, 
and  decant  the  water  and  suspended  matters  into  a  liter  flask. 
After  this  has  been  repeated  several  times,  rub  up  the  residual 
mass  and  wash  it  all  into  the  flask.  Fill  up  to  about  900  cubic 
centimeters  and  allow  to  stand  two  hours  (24  hours  in  the  case 
of  double  phosphates  with  more  than  22  per  cent,  of  soluble  phos- 
phoric acid)  ;  shaking  repeatedly,  or  shaking  continuously,  for 
half  an  hour.  Fill  up  to  the  liter  mark  and  filter  through  a  dry 
filter.  Add  100  cubic  centimeters  of  molybdate  solution  for  each 
100  milligrams  of  phosphorus  pentoxid  present,  to  portions  of 
25  or  50  cubic  centimeters  for  each  determination,  warm  to  about 
80°  for  an  hour,  filter,  and  wash  the  precipitate  with  the  ammo- 
nium nitrate  solution.  Add  a  little  molybdate  solution  to  the 
filtrate,  warm,  and,  if  a  fresh  precipitate  be  observed,  it  is  to  be 
added  to  the  first.  The  precipitate  is  dissolved  in  ammonia  and 
hydrochloric  acid  carefully  added  until  the  precipitate  caused  by 
it  only  slowly  redissolves  on  stirring.  The  phosphoric  acid  is 
precipitated  from  the  clear  liquid,  which  is  still  ammoniacal,  with 
magnesia  mixture,  using  10  cubic  centimeters  for  each  100  'milli- 
grams of  phosphorus  pentoxid  present.  This  is  added,  drop  by 
drop,  and  the  liquid  kept  stirred  during  the  addition.  Allow  to 
stand  at  least  two  hours,  filter,  wash  with  dilute  ammonia,  dry, 
and  ignite,  at  first  with  a  very  small  flame,  and  finally  with  the 
blast-lamp  or  in  a  Rossler  furnace.  To  insure  burning  to  white- 


78  AGRICULTURAL   ANALYSIS 

ness,  nitric  acid  may  be  used,  but  not  more  than  one  or  two 
drops. 

B.  Total  Phosphoric  Acid. — (i)  For  bone  and  flesh-meal, 
fish-guano,  and  similar  fertilizers  the  reagents  necessary  are  the 
same  as  before. 

Carefully  burn  five  grams  to  ash,  boil  the  ash  for  half  an  hour 
with  nitric  acid  of  1.32  specific  gravity,  dilute  with  water,  and, 
after  cooling,  dilute  to-  500  cubic  centimeters.  Filter  through  a 
dry  filter  and  add  100  cubic  centimeters  of  the  molybdate  solution 
for  each  100  milligrams  of  phosphorus  pentoxid  present  to  50 
cubic  centimeters  of  the  filtrate.  Treat  further  as  before  described. 

(2)  Phosphates,  guanos,  bone-black,  etc. 

One  gram  of  substance,  after  powdering,  and,  if  necessary, 
igniting,  is  covered  with  four  cubic  centimeters  of  hydrochloric 
acid  of  1.13  specific  gravity  and  a  little  water  and  heated  for  an 
hour  and  a  half.  Evaporate  to  dryness  without  filtration,  making 
repeated  additions  of  nitric  acid  until  no  more  vapors  of  hydro- 
chloric acid  are  evolved.  Boil  the  residue  with  nitric  acid,  cool, 
make  up  to  100  cubic  centimeters  with  water,  and  shake.  Filter 
and  treat  50  cubic  centimeters  of  the  resulting  solution  by  the 
molybdate  method  and  proceed  further  as  before  described. 

84.  Sources  of  Error  in  the  Molybdate  Method. — When  con- 
ducted with  proper  care,  the  gravimetric  molybdate  method  is  one 
of  the  most  exact  processes  known  to  analytical  chemistry. 

There  are,  however,  some  sources  of  error  in  the  process  which 
should  be  avoided  as  carefully  as  possible  or  taken  into  account. 

i.  Hrror  Due  to  Occluded  Silica. — When  silica  passes  into 
solution  in  the  original  sample,  and  this  may  be  the  case  especially 
with  mineral  phosphates,  it  may  appear  both  in  the  yellow  pre- 
cipitate and  in  the  final  magnesium  pyrophosphate.  In  all  such 
cases  the  residue,  after  ignition,  should  be  dissolved  in  hydro- 
chldric  acid  and  any  insoluble  residue  weighed  as  silica  and  de- 
ducted from  the  first  weight.  If  the  silica  be  removed  by  evap- 
orating the  solution  of  the  original  material  to  dryness,  and 
igniting  to  destroy  organic  matter,  care  must  be  taken  to  recon- 
vert all  phosphoric  acid  into  the  ortho  form  by  long  boiling  with 
nitric  acid  before  precipitation. 


SOURCES   OF   ERROR    IN   THE   MOLYBDATE   METHOD  79 

Another  method  of  avoiding  any  trouble  from  silica  consists  in 
using  sulfuric  and  a  little  nitric  acid  as  the  solvent  for  the  orig- 
inal substance.  Silica  is  not  soluble  in  hot  concentrated  sulfuric 
acid.  The  volume  of  the  sulfuric  should  be  about  ten  times  that 
of  the  nitric  acid  used,  and  the  boiling  be  continued  until  sulfuric 
vapors  are  evolved. 

2.  Error  Due  to  Arsenic— -Only  in  rare  cases  will  arsenic  be 
found  in  phosphatic  fertilizing  materials.    In  case  of  pyritic  phos- 
phates, the  iron  disulfid  may  carry  arsenic.     The  solution  in  such 
a  case  is  best  accomplished  in  hydrochloric  acid.     If  aqua  regia 
be  used,  all  nitric  acid  should  be  removed  by  repeated  evapora- 
tion with  hydrochloric  acid.  The  arsenic  can  then  be  precipitated 
in  the  hot  dilute  hydrochloric  acid  solution  by  hydrogen  sulfid. 

3.  Error  Due  to  Occluded  Magnesia. — The  danger  of  contami- 
nation of  the  final  precipitate  with  magnesium  oxid  has  been 
pointed  out  by  some  authors.    The  re-solution  of  the  precipitate 
followed  by  a  second  precipitation  is  the  usual  remedy  proposed. 
Lorenz  states  that  this  source  of  error  may  be  entirely  avoided  by 
the  addition  of  two  per  cent,   of  citric  acid  to  the  solution.54 
Without  the  addition  of  citric   acid  the  precipitation  of  some 
magnesia  with  the  phosphate,  at  least  in  strongly  ammoniacal  solu- 
tions, cannot  be  avoided  even  by  the  slowest  and  most  careful 
addition  of  the  magnesia  mixture.    The  citric  acid  is  used  in  the 
common  form  of  ammonium  citrate  solution. 

4.  Error  Due  to  Volatility  of  Phosphoric  Acid. — This  source  of 
error  has  been  made  the  subject  of  a  special  study  by  Neubauer.55 
From  the  results  a  table  has  been  constructed,  the  use  of  which 
is  recommended  for  phosphoric  acid  determinations.    The  source 
of  error  in  the  method  where  neutralization  is  omitted  lies  exclu- 
sively in  the  loss  of  phosphoric  acid  by  volatilization.    The  mag- 
nesia-covered crucible  lid  offers  a  very  good  control  of  this  error, 
and  its  use  is  recommended  to  the  analyst.    Of  course,  the  pres- 
ence of  sulfur  in  the  gas  used  for  ignition  is  liable  to  disturb  this 
check. 

54  Zeitschrift  fur  analytische  Chetnie,  1893,  82  : 64. 

55  Journal  of  the  American  Chemical  Society,    1894,    16  :  289.     Trans- 
lated and  Abridged  by  K.  P.  McElroy. 


8O  AGRICULTURAL   ANALYSIS 

The  following  course  of  procedure  in  the  determination  of 
phosphoric  acid  can  be  recommended  to  avoid  or  correct  this 
error : 

Separate  the  phosphoric  acid  in  the  form  of  the  yellow  precip- 
itate and  wash  this  latter  in  the  usual  way.  Too  high  a  heat 
should  not  be  employed,  nor  should  the  solutions  be  allowed  to 
stand  too  long,  lest  excess  of  molybdic  acid  separate.  Dissolve 
the  phosphomolybdate  in  100  cubic  centimeters  of  cold  two  and 
five-tenths  per  cent,  ammonia  and  add  as  many  cubic  centi- 
meters of  the  usual  magnesia  mixture  (55  grams  magnesium 
chlorid  and  70  grams  ammonium  chlorid  dissolved  in  a  liter 
of  two  and  five-tenths  per  cent,  ammonia)  as  there  are  centi- 
grams of  phosphorus  pentoxid  present.  Addition  should  not  be 
made  faster  than  10  cubic  centimeters  per  minute.  Stir  during 
the  addition.  After  the  precipitation  stir  briskly  once  more  and 
allow  to  stand  at  least  three  hours.  Wash  with  two  and  five- 
tenths  per  cent,  ammonia  till  the  chlorin  reaction  disappears,  dry 
the  filter,  and  introduce  into  a  well  cleaned  crucible  which  has 
been  thoroughly  ignited.  Place  the  lid  at  an  angle,  carbonize 
the  filter,  and  gradually  raise  the  heat,  though  not  higher  than 
a  medium  red  heat,  till  the  pyrophosphate  becomes  completely 
white.  When  this  happens  bring  the  blast  into  action  and  ignite 
to  constant  weight.  The  weight  finally  accepted  must  not  change 
even  after  half  an  hour's  ignition.  Upon  this  requirement  espe- 
cial stress  must  be  laid.  Pure  magnesium  pyrophosphate  does 
not  suffer  any  loss  even  after  several  hours'  ignition,  nor  does 
a  good  platinum  crucible.  To  the  weighed  amount  of  pyrophos- 
phate add  the  correction  given  in  the  table.  For  example,  if  the 
weight  be  250  milligrams,  the  correction  to  be  added  is  four  and 
two-tenths  milligrams,  and  the  correct  weight  is  then  254.2  milli- 
grams. Multiplication  of  the  sum  by  sixty-four  gives  the  amount 
of  phosphorus  pentoxid  in  the  weight  taken  for  analysis. 

When  phosphoric  acid  is  to  be  estimated  as  pyrophosphate  it 
must  always  be  first  separated  as  molybdate,  even  when  the  orig- 
inal solution  contains  no  bases  capable  of  forming  insoluble  phos- 
phates, as  otherwise  these  corrections  will  not  be  applicable. 


MODIFICATION   OF  JORGENSEN  8 

Using  these  corrections,  the  estimation  of  phosphoric  acid  be- 
comes one  of  the  most  accurate  of  known  analytical  methods. 
CORRECTION  FOR  PHOSPHORIC  ACID  DETERMINATION. 

Found,  Lost.  Found,  Lost. 

Mg2P2O7  milligrams  Mg2P8O7  milligrams 

in  grams.  Mg2P2O7.  in  grams.  Mg2P2O7. 

o.  10  0.6  0.24  4.0 

o.  12  0.8  0.25  4.2 

0.14  1.2  0.26  4.6 

0.15  1-4  0.27  5.0 

0.16  1.6  0.28  5.5 

0.17  £.4  0.29  6.T 

0.18  2.6  0.30  6.8 

0.19  3-2  0.31  7.6 

0.20  3.5  0.32  8.6 

0.21  .36  0.33  9.6 

0.22  3.8  0-34  10.6 

85.  Modification  of  Jorgensen. — Jorgensen  has  submitted  to  a 
renewed  detailed  study  the  standard  methods  of  precipitation 
of  phosphoric  acid  as  magnesium  ammonium  phosphate  for  the 
purpose  of  determining  whether  any  errors  have  crept  into  the 
usual  methods.50  He  used  as  the  basis  of  his  test  for  accuracy  bv 
preference  a  preparation  of  sodium  ammonium  phosphate  in  a 
crystalline  state,  NaNH4HPO4H2O.  He  selected  this  salt  as 
the  one  best  suited  for  testing  the  accuracy  of  the  method  and 
the  purity  of  reagent  because  it  can  be  prepared  easily  in  a  state 
of  purity  by  recrystallization  out  of  ammoniated  water.  The  crys- 
tals are  subsequently  exposed  in  the  air  until  dry.  It  is  also  a 
salt  which  has  little  tendency  to  efflorescence,  and  its  purity  can 
be  determined  without  reference  to  its  phosphoric  acid  content 
by  determining  the  loss  of  weight  upon  ignition  and  by  deter- 
mining its  content  of  ammonia.  If  these  two  determinations  show 
a  pure  salt  the  content  of  phosphoric  acid  may  be  left  out  of  con- 
sideration, since  this  is  the  material  upon  which  methods  and  solu- 
tions are  to  be  tried. 

Aside  from  the  variation  in  the  standard  of  comparison,  there 
is  little  new  in  Jorgensen's  work.  He  makes  a  few  changes  in 
the  composition  of  preparations  which  he  uses,  but  the  change  in 
no  case  is  great  enough  to  introduce  any  appreciable  difference  in 
the  manipulation. 

56  Zeitschrift  fiir  analytische  Chemie,  1906,  45  :  273. 


82  AGRICULTURAL   ANALYSIS 

Jorgensen  calls  especial  attention  to  the  tests  which  he  has 
made  on  the  influence  of  impurities  in  the  phosphatic  materials 
which  are  to  be  determined,  and  especially  of  the  maximum  quan- 
tities of  silica,  iron,  calcium,  aluminum,  or  salts  thereof,  which 
may  be  present  without  interfering  with  the  accuracy  of  the  pro- 
cess. He  also  uses  a  concentrated  molybdate  solution  of  which 
about  61  cubic  centimeters  are  necessary  for  the  precipitation  of 
0.2  gram  (P2O5)  on  the  supposition  that  one  part  of  phosphorus 
is  best  precipitated  in  the  presence  of  about  12  parts  of  molyb- 
denum. 

In  the  application  of  the  method  for  fertilizing  materials  Jor- 
gensen prefers  that  they  should  be  brought  into  solution  either 
with  hydrochloric  or  sulfuric  acids,  hydrochloric  preferred.  For 
the  conversion  of  the  pyrophosphates  into  phosphates,  however, 
nitric  acid  is  necessary.  If  the  solution  contains  about  0.2  of 
pyrophosphoric  acid  in  50  cubic  centimeters,  it  should  be  boiled 
with  10  cubic  centimeters  of  nitric  acid  of  a  specific  gravity  of 
1.4  for  a  quarter  of  an  hour,  or  2.5  of  nitric  acid  of  the  same 
strength  for  half  an  hour,  or  1.25  cubic  centimeters  for  an  hour. 
In  the  precipitation  of  the  phosphoric  acid  in  the  fertilizers,  if 
ferric  oxid  is  present  not  exceeding  in  quantity  0.22  gram, 
aluminic  oxid  in  quantity  not  exceeding  o.ii  gram,  calcium  oxid  in 
quantity  not  exceeding  0.42  gram,  and  silica  in  quantities  not  ex- 
ceeding 0.17  gram,  these  bodies  do  not  exert  any  injurious  effect. 
The  molybdate  precipitate  is  washed  about  10  times  by  decanta- 
tion  with  from  20  to  25  cubic  centimeters  of  a  nitric  acid  solu- 
tion of  ammonium  nitrate  consisting  of  about  one  per  cent,  of 
nitric  acid  to  about  five  per  cent,  of  ammonium  nitrate  in  100  parts 
of  the  solution,  and  afterwards  the  precipitate  is  dissolved  in  a 
measured  quantity  of  2.5  per  cent,  of  ammonia  in  such  a  way 
that  about  100  cubic  centimeters  of  the  solution  are  used  for 
each  0.2  gram  phosphoric  anhydrid,  with  similar  quantities  of 
phosphoric  acid  and  correspondingly  less  quantities  of  the  sul- 
phate. If  the  filter  is  not  considered  well  washed,  a  small  quan- 
tity of  water  may  be  used  afterwards  for  this  purpose.  The  solu- 
tion is  then  heated  in  a  covered  beaker  until  bubbles  of  steam 
begin  to  escape,  and  drop  by  drop  treated  with  a  neutral  mag- 


PHOSPHORIC   ACID   DETERMINATION  83 

nesium  solution  of  which  from  15  to  20  cubic  centi- 
meters are  required  for  each  0.2  gram  of  phosphoric  anhydrid 
present.  After  the  addition  of  the  magnesium  solution  and  dur- 
ing the  cooling  it  is  desirable  to  frequently  shake  the  vessel  con- 
taining the  precipitate,  especially  if  the  precipitate  has  changed 
into  the  dense,  crystalline  form,  which  is  apt  to  be  the  case,  for 
the  addition  of  the  magnesium  mixture  has  been  slow  and  there 
is  not  a  sufficient  excess  of  ammonia.  The  ordinary  stirring  ap- 
paratus which  is  used  can  give  valuable  service  at  this  point. 
The  nitration  of  the  precipitated  phosphoric  acid  should  not  take 
place  until  after  four  hours'  standing.  A  longer  time  than  four 
hours  does  not  have  any  influence  upon  the  results.  After  the 
collection  of  the  material  in  the  filter  it  is  washed  with  2.5  per 
cent,  of  ammonia.  It  is  very  convenient  to  have  the  bottom  of 
the  crystal  covered  with  precipitated  platinum,  since  in  this  case 
the  heating  over  a  blast-lamp  is  unnecessary,  the  ordinary  heating 
over  a  common  burner  being  sufficient.  For  conversion  the  factor 
0.63757  is  used.  (Log.  0.80453^-1). 

86.  Influence  of  Aluminium,  Magnesium  and  Calcium  upon  the 
Phosphoric  Acid  Determination. — In  solutions  containing  alumin- 
ium, iron,  magnesium  and  calcium  in  which  phosphoric  acid  is 
to  be  determined,  the  influence  of  these  bases  upon  the  deter- 
mination must  not  be  neglected.  Neubauer  has  called  attention 
to  this  point,  especially  in  connection  with  the  determination  of 
phosphoric  acid  in  the  hydrochloric  acid  solutions  of  soils.57 

The  well  known  fact  that  the  chlorid  of  lime  and  aluminium 
at  moderate  heating  in  the  air  and  in  water  produce  insoluble 
oxids  with  which  the  phosphoric  acid  as  an  insoluble  sulfate  is 
entangled  is  well  known.  The  chlorids  of  alkalies,  however, 
are  not  changed  by  this  heating,  and  this  difference  in  deport- 
ment is  the  principle  upon  which  Neubauer  bases  his  observations. 
Where  only  potassium  and  phosphoric  acid  are  to  be  determined 
in  a  hydrochloric  acid  solution,  for  instance,  of  a  soil,  Neubauer 
uses  the  following  process: 

A  volume  of  the  solution  corresponding  to  25  grams  of  the 
original  substance  (soil)  is  evaporated  to  dryness  in  a  platinum 

"  Die  landwirtschaftlichen  Versuchs-Stationen,  1905-6,  63  :  141. 


84  AGRICULTURAL   ANALYSIS 

dish.  If  no  chlorid  of  lime  is  contained  in  the  original  soil  be- 
fore the  evaporation  takes  place  a  half  gram  of  calcium  carbonate 
is  added  to  the  solution.  The  residue  from  drying  is  heated  care  • 
fully  and  in  order  to  avoid  too  rapid  evaporation  a  platinum  or 
nickel  plate  is  placed  between  the  source  of  the  heat  and  the 
dish.  After  complete  dryness  has  been  secured,  the  flame  is  so 
regulated  that  the  bottom  of  the  dish  containing  the  residue  is 
heated  almost  to  a  low  red  heat,  but  even  in  this  case  the  volatili- 
zation of  the  aluminium  chlorid  is  not  to  be  feared.  After  the 
vigorous  evaporation  of  the  vapors  of  hydrochloric  acid  has 
diminished  somewhat  the  platinum  or  nickel  plate  is  laid  upon 
the  top  of  the  dish.  The  mass  within  the  dish  soon  reaches  a 
condition  in  which  it  can  be  rubbed  into  a  fine  powder  by  a  glass 
rod,  after  which  it  is  heated  a  while  longer  and  stirred  contin- 
ually until  all  parts  of  the  material  are  reduced  to  a  fine  pow- 
der. After  about  an  hour  of  treatment  of  this  kind  the  organic 
substances  which  the  .solution  may  contain  are  completely  de- 
stroyed and  the  residue  is  ready  for  further  investigation. 

The  contents  of  the  dish  are  washed  in  a  125  cubic  centimeter 
flask  with  a  sufficient  quantity  of  water  to  fill  the  flask  half  full 
and  the  contents  of  the  flask  are  boiled  over  a  low  flame  for  about 
half  an  hour;  after  cooling,  the  flask  is  filled  to  the  mark,  thor- 
oughly mixed  and  filtered  through  a  very  small  dry  filter  into  a 
dry  vessel.  The  filtrate  must  be  completely  colorless  and  at  most 
only  slightly  alkaline,  and  if  the  operation  above  indicated  has 
been  properly  carried  out,  it  is  entirely  free  from  iron,  phosphoric 
acid  and  silicic  acid.  One  hundred  cubic  centimeters  of  the  fil- 
trate, corresponding  to  20  grams  of  the  original  soil,  is  the  quan- 
tity used,  if  the  volume  of  insoluble  material  is  not  taken  into 
consideration.  * 

If  a  correction  is  desired  for  this,  the  ignited  residue  is  weighed 
and  it's  volume  approximately  calculated  by  taking  into  consid- 
eration its  specific  gravity  and  weight. 

In  a  porcelain  dish  100  cubic  centimeters  of  filtrate  are  evap- 
orated to  dryness,  a  few  drops  of  hydrochloric  acid  added  and  a 
sufficient  quantity  of  platinum  chlorid  for  the  determination  of 
potassium  salts  in  the  usual  manner.  Inasmuch  as  other  salts 


PHOSPHORIC   ACID   DETERMINATION  85 

may  be  found  in  this  operation,  their  separation  is  recommended 
by  the  method  described  by  Neubauer.58 

For  the  estimation  of  phosphoric  acid  the  insoluble  residue 
obtained  in  the  estimation  of  potash  above  described  is  used. 
After  the  whole  of  the  filtrate  has  run  through  a  small  filter  upon 
which  the  reddish  brown  precipitate  has  been  collected,  replace 
in  the  flask  and  treat  with  a  dilute  sulphuric  acid  corresponding 
to  five  cubic  centimeters  of  the  concentrated  acid;  then  boil  the 
half-filled  flask  for  about  half  an  hour.  A  small  quantity  of  oxid 
sometimes  remains  very  firmly  attached  to  the  platinum  dish,  and 
for  this  reason  the  acid  is  conveniently  used  for  washing  out  the 
dish.  It  is  then  certain  that  no  trace  of  phosphoric  acid  is  lost. 
If  any  stains  remain  upon  the  platinum  dish  due  to  the  iron  they 
are  easily  removed  by  treatment  with  zinc  and  hydrochloric  acid. 

The  phosphoric  acid  which  has  passed  into  solution  corre- 
sponds to  20  grams  of  the  original  solution  (soil)  which  has  been 
extracted  and  is  conveniently  determined  by  the  molybdate  method. 
This  molybdate  method  is  recommended  because,  even  with  all 
the  care  which  has  been  exercised,  the  solution  usually  still  con- 
tains a  little  salicylic  acid.  Neubauer,  however,  highly  recom- 
mends in  this  case,  for  the  estimation  of  small  quantities  of  phos- 
phoric acid,  the  direct  weighing  of  the  yellow  precipitate.  In 
this  case  only  25  cubic  centimeters  of  the  solution  are  employed, 
corresponding  to  five  grams  of  the  soil,  and  this  is  treated  with 
25  cubic  centimeters  of  nitric  acid  of  1.2  specific  gravity,  and  the 
rest  of  the  process  is  carried  out  as  described  in  the  volumetric 
method. 

For  the  estimation  of  calcium  and  magnesium  another  portion 
of  the  solution,  corresponding  to  25  grams  of  soil,  except  in  the 
case  of  marly  soil,  where  a  smaller  quantity  is  used,  is  treated  as 
above  described,  except,  of  course,  without  the  addition  of  cal- 
cium carbonate.  The  residue  is  treated  with  water  and  the  liquid 
should  give  no  trace  of  an  acid  reaction.  Otherwise  it  is  evident 
that  the  deposition  of  the  chlorid  has  not  been  sufficiently  se- 
cured. 

According  to  the  estimated  quantity  of  calcium  from  about  two 

58  Zeitschrift  fiir  analytische  Chemie,  1904,  48: 14. 


86  AGRICULTURAL   ANALYSIS 

to  five  grams  of  ammonium  chlorid  are  added  and  the  mixture 
heated  upon  the  water  bath  until  no  further  evaporation  of  am- 
monia takes  place.  The  mixture  is  washed  in  a  125  cubic  centi- 
meter flask  and  treated  with  a  few  drops  of  ammonia,  boiled  a 
few  minutes,  cooled,  filled  to  the  mark,  filtered  through  a  small 
dry  filter  and  100  cubic  centimeters  of  the  filtrate,  corresponding 
to  20  grains  of  the  soil,  used  for  the  estimation  of  lime  and 
magnesium  by  the  usual  methods. 

Neubauer  claims  that  the  method  described  is  recommended 
particularly  by  reason  of  its  speediness.  According  to  him,  it 
also  has  other  advantages.  For  instance,  the  precipitation  by 
ammonia  and  ammonium  carbonate  is  avoided  in  which  a  slimy, 
difficultly  filterable  precipitate  is  often  produced  which  can  easily 
intertangle  notable  quantities  of  phosphoric  acid  and  potash.  The 
filtrate  from  the  iron  and  aluminium  precipitate  must,  on  account 
of  its  ammonia  and  ammonium  carbonate,  be  very  carefully  evap- 
orated to  dryness  in  order  to  avoid  loss  by  spurting. 

Finally,  one  of  the  especial  advantages  of  the  process  appears 
to  be  that  the  disturbing  influences  of  organic  substances  is  com- 
pletely eliminated  and  no  impure  potassium  platinum  chlorid  or 
brown  colored  phosphoric  acid  precipitate  is  any  longer  possible. 

This  method,  which  is  originally  designed  for  application  to 
soils,  may  be  used,  apparently,  with  advantage  in  the  examination 
of  slags  containing  small  quantities  of  potash  and  phosphoric 
acid  to  determine  their  value  as  fertilizing  material.  A  quantity 
of  phosphoric  acid  and  potash,  especially  the  latter,  which  is 
directly  soluble  in  hydrochloric  acid,  may  prove  to  be  an  index 
of  the  comparative  availability  of  these  two  plant  foods  contained 
in  slag. 

87.  The  Color  of  the  Magnesium  Pyrophosphate. — After  the  final 
ignition  of  the  magnesium  pyrophosphate,  whether  secured  by 
the  citrate  or  the  molybdate  method,  a  black  or  grayish  tint  is 
often  noticed.  This  may  be  due  to  traces  of  organic  matter 
brought  down  by  the  precipitate  and  especially  to  a  lack  of  care 
in  the  initial  ignition.  Many  devices  have  been  proposed  for 
the  purpose  of  avoiding  this  coloration,  although  general  experi- 


DETERMINATION   OF   PHOSPHORIC    ACID  AND  NITROGEN      87 

ments  have  shown  that  there  is  no  appreciable  increase  in  the 
weight  of  the  precipitate  when  colored  in  this  way. 

When  the  precipitation  is  carried  on  according  to  the  citrate 
method,  Neubauer  proposes  to  eliminate  this  coloration  by  the 
use  of  ammonium  sulfate.59  About  seven  cubic  centimeters  of  a 
saturated  solution  of  ammonium  sulfate  should  be  added  to  the 
solution  before  the  precipitation  by  the  magnesium  mixture. 
With  this  precaution  it  is  possible  to  obtain  a  perfectly  white 
precipitate  after  five  minutes  of  ignition.  The  lively  glowing  of 
the  precipitate  throughout  the  whole  mass  at  the  time  of  changing 
into  pyrophosphate  is  much  more  easily  observed  by  this  treat- 
ment than  when  the  mass  is  gray  or  black.  Even  should  the 
addition  of  the  ammonium  sulfate  solution  to  one  containing  a 
large  amount  of  lime  produce  a  precipitate  of  crystalline  calcium 
sulfate,  it  is  of  no  importance,  inasmuch  as  the  ammonium  citrate 
immediately  dissolves  large  quantities  of  the  calcium  salt. 

A  white  pyrophosphate  is  easily  obtained  by  treating  the  pre- 
cipitate on  the  gooch  after  washing  free  from  chlorids  with  a  drop 
or  two  of  ammonium  nitrate.  The  ignition  is  commenced  very 
gently  at  first  and  afterwards,  when  the  mass  is  white,  the  blast 
is  used. 

If  the  ignited  residue  be  gray  it  may  sometimes  be  whitened  by 
moistening  with  a  drop  or  two  of  nitric  acid,  burning  at  a  very 
low  temperature,  followed  by  the  blast.  There  is  no  appreciable 
difference  in  weight  between  a  gray  and  white  pyrophosphate. 

88.  Determination  of  Phosphoric  Acid  and  Nitrogen  in  the  Same 
Solution  by  Treatment  with  Sulfuric  Acid  and  Mercury. — Fertiliz- 
ing materials  which  contain  organic  nitrogen  and  phosphoric  acid, 
such  as  bones,  are  of  such  a  nature  that  it  is  often  difficult  to  ob- 
tain a  fair  sample  of  them  in  quantities  suited  to  the  direct  deter- 
mination ;  viz.,  about  one  gram.  Thus  it  often  becomes  important 
to  take  a  much  larger  quantity  of  the  material,  to  bring  it  into 
solution  and  to  take  an  aliquot  part  thereof.  It  may  also  often 
happen  that  it  is  important  to  determine  the  phosphoric  acid  in 
the  same  sample  which  has  been  used  for  the  determination  of 
the  nitrogen  by  moist  combustion  with  sulfuric  acid  and  mercury. 
59  Zeitschrift  fur  angewandte  Chetnie,  1894,  7  :  678. 


88  AGRICULTURAL   ANALYSIS 

In  this  connection,  however,  it  is  somewhat  difficult  to  avoid  the 
precipitation  of  some  of  the  mercury  with  the  phosphoric  acid. 

The  mercuric  sulfate  which  is  produced  by  the  Kjeldahl  method 
is  not  precipitated  in  the  presence  of  ammoniacal  solution  of  am- 
monium citrate,  but  there  may  be  small  quantities  of  mercurous 
salts  present  or  some  finely  divided  metallic  mercury  which  may 
contaminate  mechanically  the  phosphate  precipitate.  These  dis- 
turbing influences  may  be  removed  by  previous  treatment  with 
sodium  chlorid.  If  from  50  to  60  cubic  centimeters  of  sul- 
furic  acid  have  been  used  for  the  solution  and  oxidation  and  this 
be  made  up  to  half  a  liter,  it  will  be  sufficiently  dilute  to  permit 
an  almost  quantitative  separation  of  the  mercurous  chlorid  pro- 
duced by  treatment  with  sodium  chlorid. 

Neubauer,  who  has  proposed  this  method,  finds  that  when 
sodium  chlorid  is  used  previous  to  the  precipitation  of  the  phos- 
phoric acid,  a  precipitate  of  ordinary  size  contains,  at  most,  only 
one  milligram  of  mercury,  while  without  the  use  of  sodium  chlorid 
as  much  as  four  milligrams  may  be  found.  The  details  of  the 
method  employed  by  Neubauer  are  as  follows  :60 

Ten  grams  of  the  fertilizing  material  are  placed  in  a  half  liter 
flask  with  from  50  to  60  cubic  centimeters  of  strong  sulfuric 
acid,  two  grams  of  mercury,  and  a  little  paraffin  to  prevent  foam- 
ing. The  oxidation  is  carried  on  as  usual  in  the  Kjeldahl  method. 
The  liquid,  after  cooling,  is  diluted  with  water  and  one  cubic 
centimeter  of  a  citrate  solution  of  sodium  chlorid  added,  cooled, 
filled  to  the  mark,  filtered,  and  50  cubic  centimeters  taken  for 
the  determination  of  the  phosphoric  acid,  according  to  the  citrate 
method,  and  the  same  quantity  for  the  determination  of  the  am- 
monia by  distillation.  The  methods  of  digestion  of  soils  with 
sulfuric  acid  described  in  Volume  I,  are  also  applicable  to 
fertilizing  materials. 

THE  CITRATE  METHOD 

89.  General  Principles. — It  has  been  seen  that  in  the  molybdate 

method  there  is  introduced  a  process  at  considerable  cost,  both 

of  reagents  and  time,  having  for  its  object  the  separation  of  the 

phosphoric  acid  from  all  the  other  acids  and  bases  which  may 

80  Zeitschrift  fur  angewandte  Chemie,  1894,  7  :678. 


GENERAL,  PRINCIPLES  89 

have  been  present  in  the  original  sample.  The  phosphorus  is  thus 
obtained  in  composition  with  molybdenum  and  ammonium  in  a 
form  easily  soluble  in  ammonia,  from  which  it  can  be  accurately 
separated  by  means  of  a  soluble  salt  of  magnesia. 

The  citrate  method  has  for  its  object  the  suppression  of  this  in- 
termediate step  and  the  determination  of  the  phosphoric  acid  by 
direct  precipitation  in  presence  of  iron,  lime,  and  alumina.  The 
principle  in  which  it  is  based  rests  on  the  well  known  power  of 
an  alkaline  ammonium  citrate  to  hold  in  solution  the  salts  of  iron, 
alumina,  and  lime,  while  at  the  same  time  it  permits  of  the  separa- 
tion of  phosphoric  acid,  as  ammonium  magnesium  phosphate.  In 
no  case  can  the  citrate  method  be  regarded  as  a  rigidly  exact  an- 
alytical process,  but  large  experience  has  shown  that  the  errors 
of  the  method  are  compensatory  and  that  it  affords  a  good  and 
ready  method  for  fertilizer  control. 

When  phosphoric  acid  solutions  which  contain  no  iron,  lime, 
alumina,  or  manganese,  are  precipitated  in  presence  of  ammonium 
citrate  the  results  obtained  vary  markedly  with  the  quantity  of 
magnesia  mixture  employed.  Grupe  and  Tdlens  were  the  first 
to  point  out  that  a  portion  of  the  phosphoric  acid  might  remain 
in  solution,  but  that  the  precipitate  might  contain  a  sufficient 
excess  of  magnesia  to  compensate  for  the  loss.61  If  lime,  iron  and 
alumina,  moreover,  are  present,  the  precipitate  obtained  is  not 
wholly  free  from  these  bodies.  It  is  true  that  the  quantities  of 
these  bodies  found  in  the  precipitate  are  quite  small,  but  they  may 
at  times  influence  the  accuracy  of  the  results.  The  presence  of 
lime  and  magnesia  in  the  precipitate,  as  already  mentioned,  is 
indicated  by  the  yellow  color  produced  by  moistening  the  white 
ignited  precipitate  with  silver  nitrate.62  It  has  been  further  shown 
by  Glaser,'as  well  as  by  Neubauer,  that  a  portion  of  the  phos- 
phoric acid  may  be  lost  by  volatilization  in  the  citrate  method.68 
When  the  ignition  is  carried  on  in  a  crucible  where  the  cover  is 
coated  with  magnesia  to  intercept  the  volatilized  acid,  a  considera- 
ble quantity  of  it  can  be  recovered  by  the  molybdate  method. 

61  Journal  fur  Landwirtschaft,  1882,  30  :  23. 

6i  Tollens,  Journal  fur  Landwirtschaft,  1882,  30  :  48. 

63  Zeitschrift  fiir  angewandte  Chemie,  1894,  7  :  544- 


90  AGRICULTURAL   ANALYSIS 

Where  too  little  magnesia  mixture  is  employed,  therefore,  two 
sources  of  loss  are  to  be  guarded  against;  viz.,  a  part  of  the 
phosphoric  acid  may  remain  in  solution  and  another  part  be  vol- 
atilized on  ignition.  The  explanation  of  the  volatilization  is  as 
follows :  In  the  presence  of  ammonium  citrate,  magnesium  chlorid 
may  be  partly  converted  into  magnesium  citrate  and  ammonium 
chlorid.  There  may  be  a  time,  therefore,  in  the  precipitation 
with  not  too  great  excess  of  magnesia  mixture,  when  propor- 
tionally there  is  little  magnesium  chlorid  and  much  ammonium 
chlorid  present.  The  formation  of  a  salt  represented  by  the 
formula  2Mg(NH4)4(PO4)2  may  take  place  which,  upon  ignition, 
breaks  up  into  2Mg(PO3),  and  finally  passes  into  Mg2P2O7  with 
less  of  P2O5.  This  theoretical  condition  has  but  little  weight, 
however,  practically  in  the  analysis  of  fertilizers,  since  in  these 
cases  a  large  quantity  of  lime  is  always  present.  But  even  in 
these  cases  traces  of  volatile  P2O5  may  be  discovered. 

Wells  has  shown  that  the  citrate  method  gives  good  results 
in  certain  conditions,  but  that  this  accuracy  is  reached  by  a  for- 
tunate compensation  of  errors.6*  The  ammonium  magnesium  salt 
does  not  precipitate  all  the  phosphoric  acid  in  this  process,  but 
contains  enough  impurities  to  make  up  for  this  loss. 

Johnson  in  conjunction  with  Osborne  has  shown  that  the  re- 
sults by  the  citrate  method  practiced  in  accordance  with  the  details 
laid  down  by  Vogel,  are  too  low,  but  that  this  difficulty  could  be 
overcome  by  using  more  and  stronger  magnesia  mixture  and  a 
larger  quantity  of  strong  ammonia  solution.04  The  citrate  method 
was  found  to  give  unsatisfactory  results  when  iron  and  alumina 
were  present  in  any  considerable  quantity.  In  the  examination  of 
the  final  ignited  precipitate,  which  should  be  pure  magnesium 
pyrophosphate,  it  was  found  to  consist  of  only  from  94.98  to  97.83 
per  cent,  of  that  salt.  The  chief  impurity  found  was  calcium  oxid, 
the  percentage  of  which  varied  from  2.05  to  3.95  in  six  cases. 
There  was  also  a  considerable  percentage  of  loss  due,  probably, 
to  magnesia  and  pyrophosphoric  acid. 

The  presence  of  large  quantities  of  iron  and  alumina  also  im- 
pairs the  accuracy  of  the  molybdate  method  when  the  precipita- 
M  Journal  of  the  American  Chemical  Society,  1894,  16  : 462. 


METHOD   OF   HALLE   EXPERIMENT  STATION  91 

tion  of  the  yellow  salt  takes  place  at  too  high  a  temperature.  When 
the  temperature  of  precipitation  in  the  method  is  above  50°  the 
results  are  likely  to  be  too  high,  while  a  great  excess  of  nitric 
acid  in  the  reagent  may  produce  a  contrary  effect.  In  the  lattei 
case  the  filtrate  from  the  yellow  salt  should  be  mixed  with  addi- 
tional quantities  of  molybdate  solution  until  no  further  precipitate 
takes  place. 

Many  methods  of  conducting  the  citrate  method  have  been  pro 
posed,  but  the  best  of  them  are  based  on  the  one  elaborated  at 
the  experiment  station  of  Halle  by  Biihring,  and  which  will  be 
given  in  the  next  paragraph,  followed  by  some  other  methods  in 
use  in  other  localities. 

90.  Method  of  Halle  Agricultural  Experiment  Station.85 — 
The  citrate  method  elaborated  by  Biihring,  as  described  by  Mor- 
gen,  is  the  one  employed.66  The  principle  depends  upon  the  direct 
precipitation  of  the  phosphoric  acid  by  magnesia  mixture.  By 
the  addition  of  a  solution  of  ammonium  citrate  the  precipitation 
of  lime,  iron,  alumina  and  other  bases  is  practically  prevented. 
The  precipitate  of  ammonium  magnesium  phosphate  is  converted 
by  ignition  into  magnesium  pyrophosphate  and  weighed  as  such. 
By  the  use  of  this  method  a  part  of  the  phosphoric  acid  some- 
times escapes  precipitation  and  a  portion  of  the  other  bases  is 
sometimes  thrown  down  with  the  precipitate.  Experience  has 
shown  that  by  adhering  to  certain  precautions  the  weight  of  im- 
purities in  the  precipitate  may  be  made  to  correspond  very  nearly 
to  the  weight  of  the  phosphoric  acid  which  escapes  precipitation. 

(i)  Soluble  Acid. — The  soluble  phosphates  are  first  brought 
into  solution  in  such  a  way  that  one  liter  of  water  contains  the 
soluble  phosphoric  acid  from  20  grams  of  the  substance. 
Twenty  grams  are  rubbed  in  a  porcelain  mortar  with  water  and 
through  a  wide-necked  funnel  washed  into  a  bottle-shaped  flask 
in  which  a  little  water  has  been  previously  placed.  The  flasks  em- 
ployed are  made  of  thick  glass  in  order  to  withstand  shaking. 
After  the  substance  is  washed  in,  the  flasks  are  filled  to  the  mark 

65  Bieler  und  Schneidewind,  Die  agrikultur-chemische  Versuchsstation, 
Halle  a/S,  ihre  Einrichtung  undThatigkeit,  1892  : 56. 
86  Die  chenrische  Industrie,  1890,  13  :  135,  139. 


92  AGRICULTURAL   ANALYSIS 

and  closed  with  rubber  stoppers.  They  are  placed  upon  a  shaking 
rack,  as  indicated  in  Fig.  3,  which  is  also  furnished  with  an  ap- 
paratus for  separating  the  fine  meal  from  the  basic  slag. 

On  a  table,  as  shown  in  the  figure,  is  fastened  a  movable  hori- 
zontal board  by  means  of  hinges.  On  one  side  of  this  movable 
board  is  placed  an  open  wooden  box  in  which  is  a  perforated 
shelf  for  the  purpose  of  holding  the  flasks,  so  as  to  prevent  their 
striking  together  during  the  shaking.  On  the  other  side  is  placed 
the  sifting  apparatus  above  mentioned.  The  to  and  fro  move- 
ment of  the  shaker  is  imparted  by  any  convenient  mechanism. 

Good  results  are  obtained  by  placing  the  substance  to  be  exam- 


Fig.  3.    Shaking  Apparatus  for  Superphosphates. 

ined  in  the  flask  in  a  dry  state,  adding  800  cubic  centimeters  of 
water  and  shaking  by  means  of  the  machine  indicated  for  half 
an  hour.  Afterwards  the  flasks  are  filled  up  to  the  mark,  well 
shaken  and  their  contents  filtered  through  double  folded  filters  into 
ordinary  flasks  of  about  400  cubic  centimeters  capacity.  Before  any 
of  the  filtrate  is  collected  the  first  that  runs  through  should 'be 
well  shaken  in  the  receiving  flasks  and  rejected.  Fifty  cubic  centi- 
meters of  the  filtrate  thus  collected,  corresponding  to  one  gram 
of  the  substance,  should  be  used  for  the  determination. 

(2)  Total  Acid. — For  total  phosphoric  acid,  including  the  in- 
soluble portions,  except  in  the  case  of  basic  slags,  the  material  is 
treated  as  follows :  Five  grams  of  the  substance  are  placed  in  a 


METHOD   OF   HALLE   EXPERIMENT   STATION  93 

500  cubic  centimeter  flask  with  20  cubic  centimeters  of  nitric 
acid  of  1.42  specific  gravity,  and  50  cubic  centimeters  of  pure 
concentrated  sulfuric  acid,  and  boiled  briskly  for  half  an  hour. 
With  substances  which  contain  much  organic  material,  a  little 
paraffin  is  added  to  avoid  frothing.  Such  substances  also  require 
a  larger  quantity  of  nitric  acid  than  that  above  specified.  The 
flasks  are  allowed  to  cool,  water  added,  again  allowed  to  cool, 
and  filled  up  to  the  mark  at  17°. 5.  If  hydrochloric  instead  of 
sulfuric  acid  be  used  in  making  the  above  solution,  when  the 
citrate  method  is  employed,  the  results  are  always  too  high,  be- 
cause the  precipitate  contains  lime  and  alumina  in  such  quantities 
as  to  render  any  compensation  for  them  inaccurate.  In  addition 
to  this  the  sulfuric  has  this  great  advantage  over  the  hydro- 
chloric acid;  viz.,  it  does  not  separate  the  silicic  acid,  inasmuch 
as  silicic  acid  is  insoluble  in  boiling  sulfuric  acid. 

(3)  Citrate-Soluble  Acid. — As  is  well  known,  in  acidulated 
phosphate  a  part  of  the  phosphoric  acid  at  first  soluble  in  water 
becomes  insoluble,  or,  as  usually  expressed,  reverted.  This  por- 
tion, however,  is  still  soluble  in  ammonium  citrate.  By  the  Halle 
method  it  is  determined  as  follows:  Two  grams  of  the  sample 
are  digested  with  100  cubic  centimeters  of  ammonium  citrate  so- 
lution, 1.09  specific  gravity,  for  half  an  hour  at  50°  in  a  beaker. 
Afterwards  the  soluble  matter  is  separated  by  filtration  with  the 
aid  of  a  filter-pump  and  the  residue  washed  with  a  solution  of  one 
part  water  and  one  part  citrate  solution  until  all  the  dissolved 
phosphoric  acid  is  removed  from  the  filter.  Generally  three  or 
four  washings  are  sufficient.  The  residue  on  the  filter  is  dried, 
ignited  and  dissolved  in  a  mixture  of  two  cubic  centimeters  of 
nitric  and  20  cubic  centimeters  of  sulfuric  acid,  the  solution 
made  up  to  a  volume  of  200  cubic  centimeters,  filtered,  and  100 
cubic  centimeters  of  the  filtrate  used  for  the  determination.  The 
.acid  in  the  filtrate  is  nearly  neutralized  and  50  cubic  centimeters 
of  the  citrate  solution  used  in  the  determination  of  total  acid  are 
added,  and  afterwards  25  cubic  centimeters  of  magnesia  mix- 
ture and  20  cubic  centimeters  of  24  per  cent,  ammonia.  After 
.•standing  for  48  hours,  the  precipitate  is  separated  by  filtration, 
ignited,  and  weighed  in  the  usual  way.  The  difference  be- 


94  AGRICULTURAL   ANALYSIS 

tween  the  total  phosphoric  acid  and  that  in  the  insoluble  residue, 
after  treatment  with  ammonium  citrate,  as  above,  gives  the 
quantity  of  phosphoric  acid  soluble  in  citrate  solution.  The 
difference  between  the  total  citrate-soluble  and  the  water-soluble 
gives  the  quantity  of  the  reverted  phosphoric  acid. 

The  ammonium  citrate  solution  (Petermann's)  used  for  the  di- 
gestion is  made  as  follows :  Two  hundred  and  fifty  grams  of  crys- 
tallized citric  is  dissolved  in  half  a  liter  of  hot  water,  diluted 
with  550  cubic  centimeters  of  water,  276  cubic  centimeters  of 
24  per  cent,  ammonia  added,  and  finally,  exactly  neutralized  by 
adding,  little  by  little,  50  per  cent,  citric  acid  solution. 

The  Halle  methods  of  separating  the  water  and  citrate-soluble 
acids  appear  to  be  less  complete  and  reliable  than  those  in  use 
by  the  Official  Agricultural  Chemists  of  this  country.  The  pre- 
cipitation of  basic  phosphates,  when  large  quantities  of  water  are 
used  at  once  in  separating  soluble  acid,  must  tend  to  diminish 
the  quantity  obtained,  while  the  lack  of  care  in  assuring  the  neu- 
trality of  the  citrate  solution  might  lead  to  varying  results. 

(4)  Double  Superphosphates. — In  the  case  of  double  super- 
phosphates, which  sometimes  contain  large  quantities  of  pyro- 
phosphate,  the  solution  is  made  in  the  usual  way  so  that  in  100 
cubic  centimeters  there  will  be  contained  two  grams  of  the  sub- 
stance.    Usually  10  grams  are  used  and  the  volume  made  up 
to  half  a  liter.    Twenty-five  cubic  centimeters  of  the  filtrate  are 
diluted    with    75    cubic    centimeters    of    water    and    the    pyro- 
converted  to  orthophosphoric  acid  by  heating  with  10  cubic  centi- 
meters of  strong  nitric  acid  on  a  sand-bath.    The  heating  should 
be  continued  until  the  volume  is  reduced  to  25  cubic  centimeters. 
The  strongly  acid  liquid  is  made  alkaline  with  ammonia  and  after- 
wards slightly  acid  with  nitric  acid,  and  the  rest  of  the  process 
is  carried  on  in  the  usual  way. 

(5)  Phosphoric  Acid  in  the  Residue  of  Superphosphate  Manu- 
facture.— In  the  mixture  of  superphosphates  and  gypsum,  the  res- 
idue of  the  manufacture  of  double  superphosphates,  the  phos- 
phoric acid  is  estimated  in  the  following  manner:     Five  grams 
of  the  substance  are  placed  in  a  dish,  rubbed  up  with  absolute  al- 
cohol, and  washed  into  a  250  cubic  centimeter  flask.    The  flask  is 


METHOD   OF   HALLE   EXPERIMENT   STATION  95 

filled  with  absolute  alcohol  to  the  mark,  closed  with  a  stopper, 
and,  with  frequent  shaking,  allowed  to  stand  for  two  hours ;  it  is 
thereupon  filtered  as  quickly  as  possible;  50  cubic  centimeters  of 
the  filtrate,  corresponding  to  one  gram  of  the  substance,  is  used 
for  the  estimation.  This  is  evaporated  on  a  sand-bath  to  a  sirupy 
consistence,  diluted  with  water  and  treated  as  in  the  case  of  the 
soluble  phosphates  above  mentioned.  In  all  cases,  as  described 
above,  after  the  solutions  are  obtained  they  are  treated  with  the 
ammonium  citrate  solution  and  the  phosphoric  acid  estimated  as 
in  the  method  for  soluble  acid. 

(6)  Solutions  Employed. — 

(a)  The  citrate  solution  is  made  as  follows :  Fifteen  hundred 
grams  of  citric  acid  are  dissolved    in    water,    treated   with    five 
liters  of  24  per  cent,  ammonia,  and  made  up  to  15  liters. 

(b)  The  magnesia  mixture  is  made  as  follows:  Five  hundred 
grams  of  magnesium  chlorid,  1050  grams  of  ammonium  chlorid, 
three  and  five-tenths  liters  of  24  per  cent,  ammonia,  and  six  and 
five-tenths  liters  of  distilled  water  are  used. 

In  the  case  of  the  superphosphates  50  cubic  centimeters  of 
the  citrate  solution  are  employed  and  with  the  basic  slags  100 
cubic  centimeters;  and  in  both  cases  25  cubic  centimeters  of  the 
magnesia  mixture. 

(7)  Details  of  the  Manipulation. — On  the  addition  of  the  citrate 
solution  there  should  be  no  permanent  troubling  of  the  liquid,  but 
any  precipitate  at  first  formed  should  entirely  disappear  after  the 
addition  of  the  whole  quantity  of  the  reagent.     In  order  to  facili- 
tate this,  after  the  addition  of  the  citrate  solution  the  flasks  should 
be  gently  shaken  so  as  to    distribute    the    solution    throughout 
the    mass.      Solutions    from    bone-black    superphosphates    show 
scmetimes,  after  the  addition  of  the  citrate  solution,  a  more  or 
less  strong  opalescence,  but  this  opalescence  does  not  influence 
the  results.     Should  it  happen  that  with  superphosphates  which 
are  made  from  raw  material  containing  large  excesses  of  iron  or 
clay  50  cubic  centimeters  of  the  citrate  solution  are  not  suffi- 
cient to  prevent  the  other  bases  from  being  precipitated,  an  addi- 
tional   quantity   up   to   25    cubic    centimeters    may   be    added. 
The  addition  of  the  magnesia  mixture  must  follow  as  quickly  as 


96 


AGRICULTURAL   ANALYSIS 


possible  after  the  addition  of  the  citrate  solution  to  avoid  a  sep- 
aration of  crystalline  calcium  phosphate.  On  the  addition  of  the 
citrate  solution  there  is  always  a  rise  in  temperature.  Inasmuch 
as  the  precipitation  of  the  phosphoric  acid  with  magnesia  must 
take  place  in  the  cold,  the  liquid  must  be  cooled  after  the  addi- 
tion of  the  citrate,  and  the  cooling  should  take  place  as  quickly 
as  possible. 

The  above  method  was  adopted  by  the  chemical  section  of  the 
International  Agricultural  Congress  held  at  Vienna,  September, 
i890.67 

In  order  to  hasten  the  precipitation  of  the  ammonium  magne- 
sium phosphate  and  to  prevent  the  fixation  of  the  precipitate  on 
the  walls  of  the  erlenmeyer,  the  flask  should  be  shaken  for  half 
an  hour.  For  this  purpose  the  flasks  should  be  closed  with  smooth 
well-fitting  rubber  stoppers  and  placed  in  a  shaking  machine.  The 
shaking  machine  of  the  form  given  in  Fig.  4,  recommended  by 
the  Halle  station,  is  very  conveniently  used  for  this  purpose. 


Fig.  4.    Shaking  M*achine  for  Ammonium  Magnesium  Phosphate. 

On  a  vertical  axis  are  carried  two  platforms  for  holding  the 
flasks.  The  flasks  are  prevented  from  striking  each  other  by 
means  of  the  partitions  shown.  The  apparatus  is  conveniently 
driven  by  a  small  water-motor,  as  indicated,  which  imparts  to  the 
platforms  a  partial  back  and  forth  revolution. 

After  shaking  for  half  an  hour,  any  precipitate  adhering  to  the 
rubber  stoppers  is  carefully  washed  off  with  ammonia  water  into 
the  flask.    The  filtration  can  be  made  immediately  after  the  shak- 
ing or  after  two  or  three  days ;  the  results  are  the  same. 
•T  Chemiker-Zeitung,  1890,  14  :  1246. 


METHOD   OF    HAIXE   EXPERIMENT   STATION 


97 


The  filtration  of  the  ammonium  magnesium  phosphate  is  made 
through  gooches.  The  asbestos  felt  is  prepared  in  the  following 
way :  The  coarse  fibers  of  asbestos  are  chopped  up  with  a  sharp 
knife  on  a  glass  plate  and  boiled  for  two  hours  with  strong  hydro- 
chloric acid ;  afterwards,  by  repeated  washing  with  distilled  water, 


Fig.  5.    Rossler  Ignition  Furnace. 

they  are  freed  from  acid  and  the  fine  particles  of  asbestos  which 
would  tend  to  make  the  filter  too  impervious.  After  the  last  wash- 
water  is  poured  off,  the  asbestos  is  suspended  in  water  and  used 
for  making  the  felt  on  the  filter.  The  preparation  of  the  crucible 
and  the  filtration  under  pressure  are  accomplished  in  the  usual 
way. 

The  ignition  of  the  precipitate  is  accomplished  in  a  Rossler  ig- 


98  AGRICULTURAL   ANALYSIS 

nition  oven,  Fig.  5.  When  the  muffle  of  the  furnace  shows  a 
white  heat  or  a  white-red  heat,  it  is  at  the  proper  temperature  for 
the  estimation.  At  higher  temperatures,  the  filtering  property 
of  the  asbestos  felt  is  easily  injured.  Generally,  an  ignition  of  five 
minutes  is  sufficient,  but  with  double  superphosphates,  10  min- 
utes are  required. 

91.  The  Swedish  Citrate  Method.08 — This  method  of  determina- 
tion is  a  modification  of  the  citrate  method  already  described  and 
is  founded  on  the  observation  that  phosphoric  acid  in  the  pres- 
ence of  calcium  salts,  without  the  necessity  of  previously  con- 
verting into  phosphomolybdate,  is  precipitated  directly  by  mag- 
nesia mixture  from  a  solution  to  which  ammonium  citrate  has 
been  added,  provided  first,  that  the  solution  contain  a  sufficient 
quantity  of  sulfuric  acid  to  convert  all  the  calcium  compounds 
into  sulfates,  and  second,  that  only  as  much  citrate  be  added  as 
is  required  to  keep  the  calcium  salts  in  alkaline  solution.  In  other 
words,  it  is  the  method  of  separation  devised  by  C.  Glaser  and 
others.69 

Reagents,  (i)  Citric  Acid  Solution. — Prepared  by  dissolving 
500  grams  of  citric  acid  in  water  and  completing  to  a  volume  of 
one  liter. 

(2)  Ammonia  of  0.959  specific  gravity. 

(3)  Magnesia  Mixture,  composed  of  140  grams  of  magnesium 
sulfate,  150  grams  ammonium  sulfate,  and  30  grams  of  chlorid  of 
ammonium  dissolved  in  350  cubic  centimeters  of  16  per  cent,  am- 
monia and   1650  cubic  centimeters  of  water.     The  ammonium 
chlorid  is  added  to  prevent  the  precipitation  of  basic  magnesium 
sulfate. 

The  various  processes  are  conducted  as  follows : 
(a)    Water-Soluble  Phosphoric  Acid. — Add   20   cubic   centi- 
meters of  citric   acid  solution  to  50  cubic  centimeters  of  the 
water-soluble  solution  obtained  according  to  the  Swedish  molyb- 
date  method,  and  then  add  33  cubic  centimeters  of  ammonia. 
68  Official  Swedish  Methods  Translated  for  the  Author  by  F.  W.  Woll. 
89  Zeitschrift  fur  analytische  Chemie,  1885,  24  : 178;  1886,  25  :  416. 
Chemiker-Zeitung,  1888,  12  =85,492. 
Zeitschrift  fur  angewandte  Chemie,  1888,  1  :  354. 
Die  landwirtschaftlichen  Versuchs-Stationen,  1888,  35  : 439. 


METHODS   ADOPTED   BY   THE    BRUSSELS   CONGRESS  99 

When  the  mixture  has  cooled,  add  slowly  25  cubic  centimeters 
of  the  magnesia  mixture,  and  then  42  cubic  centimeters  of  the 
ammonia.  Keep  the  solution  stirred  by  means  of  a  closely 
clipped  feather  which  is  pressed  tightly  against  the  sides  of  the 
beaker;  by  this  process  the  phosphate  is  precipitated  after  half 
an  hour  in  pure  condition  and  completely  without  in  the  least 
sticking  to  the  wall  of  the  beaker;  filter,  wash,  and  ignite,  as 
usually  directed. 

(&)  Insoluble  PhosphoHc  Acid. — Moisten,  in  a  porcelain  dish, 
10  grams  of  the  powdered  sample  with  water;  add  50  cubic 
centimeters  of  concentrated  sulfuric  acid,  and  heat  for  15  min- 
utes so  that  fumes  of  sulfuric  acid  will  escape.  When  the  mass 
has  cooled,  wash  it  into  a  half-liter  graduated  flask,  fill  to 
the  mark,  and  shake  well.  After  filtration,  the  clear  filtrate  may, 
after  some  time,  turn  turbid  by  separation  of  calcium  sulfate,  but 
as  the  ammonium  citrate,  which  is  afterwards  added,  again  brings 
the  precipitate  into  solution,  it  is  of  no  importance.  Add  to  50 
cubic  centimeters  of  the  solution,  corresponding  to  one  gram  of 
the  powdered  sample,  20  cubic  centimeters  of  the  citric  acid 
solution,  neutralize  the  mixture  approximately,  but  not  exactly, 
by  ammonia ;  after  cooling,  add  25  cubic  centimeters  of  magnesia 
mixture;  stir  the  fluid  by  means  of  a  feather,  as  described,  till 
no  more  precipitate  is  formed,  and  finally  add  33  cubic  centi- 
meters of  ammonia  while  stirring  for  several  minutes  longer; 
after  half  an  hour  the  precipitate  may  be  separated  by  filtration, 
washed,  and  ignited,  as  usually  directed. 

The  above  process  is  essentially  the  one  used  with  basic  slags. 
When  much  organic  matter  is  present,  by  continuing  the  heating 
with  sulfuric  acid  for  some  time  it  may  be  destroyed. 

92.  Methods  Adopted  by  the  Brussels  Congress,  1894. — The  re- 
port of  the  committee  on  methods  of  analysis  of  phosphoric  acid 
requires  the  molybdate  method  to  be  used  in  all  cases  where  the 
quantity  to  be  determined  is  very  small.  In  other  cases  the  citrate 
method  may  be  employed.70 

(i)  Soluble  Phosphoric  Acid. — The  soluble  phosphoric  acid  is 
determined  by  the  method  adopted  at  Brussels  in  the  following 

70  L'Engrais,  1894,  9  :  928. 


100  AGRICULTURAL   ANALYSIS 

manner:  Five  grams  of  the  sample  are  rubbed  to  a  powder  in  a 
mortar,  and  then  from  50  to  60  cubic  centimeters  of  water 
added.  After  allowing  to  settle  for  a  few  minutes  the  liquid  por- 
tion is  decanted  upon  a  filter.  This  operation  is  repeated  three  or 
four  times.  Finally,  the  solid  portions  are  washed  upon  the  filter, 
and  the  washing  with  water  is  continued  until  the  filtrate  amounts 
to  about  three-quarters  of  a  liter.  A  few  drops  of  hydrochloric 
acid  are  added  until  the  filtrate  is  perfectly  clear,  and  the  volume 
is  then  made  up  to  one  liter.  Fifty  cubic  centimeters  of  the  solu- 
tion are  then  treated  with  30  cubic  centimeters  of  ammonium 
citrate  solution  and  one-third  as  much  ammonia.  Afterwards 
30  cubic  centimeters  of  magnesia  mixture  are  added,  drop  by 
drop,  with  constant  stirring. 

For  superphosphates  containing  more  than  18  per  cent, 
of  phosphoric  acid  only  one  gram  of  the  sample  is  used,  for  ordi- 
nary superphosphates  two  grams,  and  for  compound  fertilizers 
four  grams.  The  sample  is  first  treated  as  above  for  soluble  acid 
until  the  filtrate  amounts  to  200  cubic  centimeters,  then  clarified 
with  a  drop  of  nitric  acid,  and  made  up  to  a  quarter  of  a  liter. 

(2)  Reverted  Phosphoric  Acid. — The  filter  containing  the  resi- 
due is  then  introduced  into  a  quarter  liter  flask  and  treated  with 
100  cubic  centimeters  of  Petermann's  alkaline  ammonium  citrate 
solution,  vigorously  shaken,  and  left  at  room  temperature  for 
15  hours.  It  is  digested  for  an  hour  at  40°  and  filtered.  Fifty 
cubic  centimeters  of  the  filtrate  are  placed  in  a  flask  and,  with 
constant  shaking,  35  cubic  centimeters  of  magnesia  mixture  added. 
The  aqueous  solution  is  treated  in  the  same  way.  The  precipi- 
tate is  collected,  washed  with  two  and  one-half  per  cent,  ammonia 
until  the  chlorin  disappears,  ignited,  weighed,  and  the  number 
obtained  multiplied  by  0.64  for  phosphoric  acid.  The  total  acid  is 
determined  in  the  usual  way. 

93.  Dutch  Method  for  Citrate-Soluble  Phosphoric  Acid. — The 
reagents  necessary  are : 

(i)  Citrate  solution.  Dissolve  165  grams  of  citric  acid  in 
700  cubic  centimeters  of  water,  mix  with  250  cubic  centimeters 
of  ammonia  of  0.92  specific  gravity,  and,  aft?r  co:ling,  bring  to 
the  volume  of  one  liter. 


METHOD   OF   LASNE  IOI 

(2)  Magnesia  mixture.  Dissolve  400  grams  of  crystallized 
magnesium  chlorid,  800  grams  of  ammonium  chlorid,  and  1600 
cubic  centimeters  of  ammonia  of  0.96  specific  gravity  in  water, 
and  dilute  to  five  liters. 

The  quantity  used  for  the  analysis  is  five  grams  where  the  fer- 
tilizer contains  less  than  six  per  cent,  of  phosphoric  acid  (mixed 
fertilizers)  ;  two  grams  where  it  contains  more  than  six  and  less 
than  15  per  cent,  (common  superphosphates)  ;  and  one  gram 
where  it  contains  more  than  15  per  cent,  (double  superphos- 
phates). Place  the  weighed  substance  in  a  mortar  and  cover 
with  loo  cubic  centimeters  of  citrate  solution.  Gently  rub  up, 
wash  into  a  half  liter  flask,  and  heat  on  a  water  bath  for  an  hour 
to  a  temperature  between  35°  and  38°.  Allow  to  cool,  fill  up  to 
500  cubic  centimeters,  and  filter  through  a  dry  double  filter.  If 
the  liquid  is  not  clear  at  the  first  titration,  pour  through  the  filter 
again,  repeating  this  till  clearness  is  attained.  To  100  cubic  centi- 
meters of  the  filtrate  add  75  cubic  centimeters  of  magnesia  mix- 
ture, allowing  the  latter  to  flow  into  the  former  very  slowly,  and 
constantly  stirring  during  the  influx.  Allow  to  stand  15  hours, 
filter,  wash  with  ammonia  of  0.96  specific  gravity,  dry,  ignite,  and 
weigh. 

The  per  cent,  of  phosphoric  acid,  except  where  otherwise  indi- 
cated, is  always  to  be  given  as  per  cent,  of  phosphorus  pentoxid 

(P205). 

94.  Method  of  Lasne. — Lasne  recalls  some  previous  observations 
which  are  confirmed  by  later  ones,  as  follows  :71 

(1)  The  precipitation  of  ammonio-magnesium  phosphate  takes 
place  without  loss  when  conducted  in  the  presence  of  citrate  of 
ammonia,  and  with  a  sufficient  excess  of  magnesia. 

(2)  Lime,  oxid  of  iron,  alumina  and  manganese  are  carried 
down  by  the  precipitate. 

(3)  The  presence  of  silica  and  of  fluo-silicates  causes  an  excess 
of  weight  in  the  precipitate  over  the  probable  amount  due  to  phos- 
phorus. 

(4)  Without  the  addition  of  an  excess  of  magnesia  the  precipi- 

71  Bulletin   de  la  Societ£  chimique  de  Paris,  1897,    [3],    17:823  and 
following. 


102  AGRICULTURAL  ANALYSIS 

tation  is  incomplete  and  the  separated  liquid  is  precipitated  alike 
b\  magnesia  and  phosphoric  acid. 

The  results  of  the  work  show  that  when  stirred  with  ammonio- 
magnesium  phosphate  the  final  result  is  -obtained  without  any  loss, 
and  that  on  calcination  the  identical  weight  with  which  the  experi- 
ment commenced  is  obtained.  The  conclusions  obtained  by  Lasne 
from  a  large  mass  of  analytical  data  are  summarized  as  follows : 

(1)  The  formation  of  phosphoric  acid  in  the  state  of  pyrophos- 
phate  without  any  other  precaution  than  previous  elimination  of 
silica  gives  results  which  are  not  affected  by  any  systematic  error. 

(2)  Rapid  precipitations  cause  an  excess  of  weight  in  the  pre- 
cipitate due  to  a  partial  formation  of  tri-magnesium  phosphate, 
which  is  only  transformed  into  ammonio-magnesium  phosphate  by 
contact  for   16  hours  with   a   sufficiently  concentrated  solution 
of  ammonium  citrate,  namely,  containing  ten  grams  of  citric  acid 
in  150  cubic  centimeters  of  the  solution.     It  is  necessary,  there- 
fore, in  order  to  obtain  rrgorous  results,  to  allow  the  precipitate 
to  stand  before  filtering  for  at  least  16  hours.     Nevertheless,  it 
must  be  admitted  that  this  excess  of  weight  is  so  small  as  not  to 
warrant  the  complete  rejection  of  the  rapid  methods  for  all  in- 
dustrial purposes  when  proper  precautions  are  employed. 

(3)  The  transformation  of  tri-magnesium  phosphate  into  am- 
monio-magnesium phosphate  takes  place  very  slowly  in  the  pres- 
ence of  ammonium  chlorid  alone,  and  there  should  always,  there- 
fore, in  these  precipitations,  be  added  the  quantity  of  citrate  of 
ammonia  indicated  above. 

The  precipitation  of  magnesia  in  the  presence  of  an  excess  of 
ammoniacal  phosphate  gives,  in  addition  to  ammonio-magnesium 
phosphate,  a  phosphate  poorer  in  magnesium,  and  as  much  poorer 
as  the  excess  of  phosphoric  acid  is  larger.  The  determination  of 
magnesia  by  this  classical  method  is  always  erroneous. 

95-  Comparative  Accuracy  of  the  Citrate  and  Molybdate  Meth- 
ods.— The  general  use  of  the  citrate  method  of  determining  phos- 
phoric acid  by  the  German  chemists  has  led  Johnson  to  review 
some  trials  of  that  method  in  his  laboratory  made  as  early  as 
i88o.72  These  determinations  have  lately  been  repeated  in  com- 
71  Journal  of  the  American  Chemical' Society,  1894,  16  :  462. 


CITRATE    AND    MOLYBDATB  METHODS  103 

parison  with  the  ordinary  molybdate  methods,  with  the  result 
that  in  67  determinations  on  bone-dust,  superphosphate, 
cotton-hull  ashes,  cottonseed-meal,  tankage,  bone-char,  phosphatic 
guano,  and  phosphate  rock,  only  three  citrate  results  differed  from 
those  obtained  by  the  molybdate  method  by  more  than  three- 
tenths  of  one  per  cent.  The  greatest  discrepancy  between  the  two 
methods  was  0.41  per  cent.,  and  the  average  difference  was  0.09 
per  cent. 

Attention  has  already  been  called  to  the  fact  that  the  citrate 
method  was  found  to  give  poor  results  when  iron  and  alumina 
were  present  in  considerable  quantity.  Ignited  precipitates  by  the 
citrate  method  were  found  to  contain  as  high  as  four  per  cent,  of 
lime,  and  iron  and  alumina  in  small  quantities  when  these  bodies 
were  abundant  in  the  original  substance. 

In  the  molybdate  method  the  rapid  precipitation  from  solutions 
at  65°  was  found  to  give  unsatisfactory  results  and  it  was  found 
necessary  to  conduct  the  process  at  temperatures  between  40°  and 
50°.  With  a  relative  excess  of  nitric  or  a  relative  deficiency  of 
molybdic  acid  some  phosphoric  acid  may  easily  escape  precipita- 
tion. The  chief  objection  to  precipitating  at  65°  is  found  in  the 
fact  that  in  presence  of  considerable  iron  and  alumina  some  of 
these  bodies  may  be  found  in  the  yellow  precipitate,  whence  they 
pass  to  the  final  ammonium  magnesium  phosphate. 

The  citrate  method,  therefore,  only  gives  safe  results  by  com- 
pensating errors  which  in  every  class  of  phosphates  must  be  em- 
pirically determined. 

The  molybdate  method  gives  results  too  high  when  iron  and 
alumina  are  present  in  considerable  quantity  and  the  yellow  pre- 
cipitate is  obtained  at  temperatures  above  50°.  On  the  other  hand, 
if  there  be  a  great  relative  excess  of  nitric  acid  the  results  may 
be  too  low  unless  the  filtrates  from  the  yellow  precipitate  be  mixed 
with  additional  molybdic  solution  and  digested  until  no  further 
precipitate  is  formed. 

Comparative  determinations  made  by  both  methods  by  Maercker 
for  the  Association  of  German  Experiment  Stations  have  led  to 
the  conclusion  that  both  give  practically  the  same  results  when 


104  AGRICULTURAL   ANALYSIS 

each  one  is  conducted  with  the  proper  precautions  peculiar  to  it.73 
In  the  latter  part  of  1892,  at  the  general  meeting  of  the  associa- 
tion, it  was  declared  that  the  citrate  method,  after  having  been 
subjected  to  repeated  tests,  was  found  to  be  satisfactory,  changing 
the  composition  of  the  solution  so  that  it  might  have  noo  instead 
of  looo  grams  of  citric  acid  and  four  liters  of  24  per 
cent,  ammonia  to  each  10  liters.  The  data  afforded  by  the  citrate 
method,  when  applied  to  an  artificial  mixture  of  known  composi- 
tion, were  more  satisfactory  than  those  obtained  by  the  molyb- 
dic  process. 

In  the  laboratory  of  the  Bureau  of  Chemistry  the  citrate  method 
has  been  found  to  give  nearly  agreeing  results  with  the  old  pro- 
cess. It  is  much  shorter  and  less  expensive,  and  is  recommended 
most  favorably  for  practical  use,  with  the  suggestion,  however, 
that,  with  every  new  kind  of  phosphate  or  phosphatic  fertilizer 
varying  notably  in  composition  from  the  standard,  the  work  should 
be  checked  at  first  by  comparison  with  the  molybdate  method.  The 
later  investigations  carried  on  by  the  Association  of  Official  Agri- 
cultural Chemists  have  served  only  to  confirm  the  superiority  of 
the  molybdate  gravimetric  method  for  all  purposes  where  great  ac- 
curacy is  demanded  and  have  shown  that  for  speed  and  con- 
venience the  volumetric  method  already  outlined  and  later  to  be 
described  in  full,  is  to  be  preferred  to  all  other  quick  processes. 

96.  The  Citrate  Precipitate  Purity. — Jorgensen  recommends  the 
following  as  the  safest  form  of  citrate  precipitation.  The  phos- 
phoric acid  solution  is  treated  with  25  cubic  centimeters  of 
neutral  ammonium  citrate  solution  or,  in  case  it  contains  a  large 
quantity  of  calcium  salts,  with  30  cubic  centimeters,  and  then 
25  cubic  centimeters  of  a  10  per  cent,  ammonia  solution  is 
added,  and  the  mixture,  in  a  covered  dish,  heated  to  the  boil- 
ing point,  and,  according  to  the  quantity  of  the  phosphate  pre- 
cipitate, treated  with  30  or  40  cubic  centimeters  of  the  neutral 
magnesium  chlorid  solution.  By  vigorous  stirring  or  shaking 
the  precipitate  crystallizes,  and  after  standing  at  least  four 
hours  is  filtered.  If  very  small  quantities  of  phosphoric  acid 
are  present  the  mixture  should  be  left  at  least  24  hours 
"  Die  landwirtschaftlichen  Versuchs-Stationen,  1892,  41  :  329. 


THE   CITRATE   METHOD  105 

before  filtering.  In  the  practice  of  this  method  the  presence  of 
aluminum  oxid  not  exceeding  0.6  gram,  or  ferric  oxid  not  ex- 
ceeding o.u  gram,  may  be  present,  but  not  in  greater  quantities 
than  these.  Calcium  oxid  should  also  not  be  present  in  quantities 
exceeding  0.03  gram. 

Detailed  data  are  given  by  Jorgensen  in  connection  with  the 
general  determinations  of  all  forms  of  phosphoric  acid,  but  they 
do  not  differ  sufficiently  from  those  already  cited  to  warrant 
their  insertion  in  full  in  this  manual.  The  student  who  desires  to 
study  in  complete  detail  this  latest  contribution  to  the  methods 
of  determining  phosphoric  acid  should  consult  the  original  article.74 

97.  The  Citrate  Method  Applied  to  Samples  with  Small  Content 
of  Phosphoric  Acid. — It  is  well  established  that  the  citrate  method 
does  not  give  satisfactory  results  when  applied  to  samples  con- 
taining small  percentages  of  phosphoric  acid,  especially  when 
these  are  of  an  organic  nature,  as,  for  instance,  cottonseed  cake- 
meal.  An  attempt  has  been  made  to  remedy  this  defect  in  the 
process  so  as  to  render  the  use  of  the  method  possible  even  in 
such  cases.75  Satisfactory  results  have  been  obtained  by  adding 
to  the  solution  of  the  cake-meal  a  definite  volume  of  a  phosphate 
solution  of  known  strength.  Solutions  of  ordinary  mineral  phos- 
phates are  preferred  for  this  purpose.  The  following  example  will 
show  the  application  of  the  modified  method : 

In  a  sample  of  cake-meal  (cottonseed  cake  and  castor  pomace) 
the  content  of  phosphoric  acid  obtained  by  the  molybdate  method 
was  2.52  per  cent. 

Determined  directly  by  the  citrate  method,  the  following  data 
were  obtained : 

Allowing  to  stand  30  hours  after  adding  magnesia  mixture, 
1.08  and  1.53  per  cent,  in  duplicates. 

Allowing  to  stand  72  hours  after  adding  magnesia  mixture, 
2.17  and  2.30  per  cent,  in  duplicates. 

In  each  case  50  cubic  centimeters  of  the  solution  were  used, 
representing  half  a  gram  of  the  sample. 

In    another    series    of    determinations    25    cubic    centimeters 

74  Zeitschrift  fur  analytische  Cheniie,   1906,  45  :  273. 

75  Journal  of  the  American  Chemical  Society,  1895,  17  :  513. 


106  AGRICULTURAL   ANALYSIS 

of  the  sample  were  mixed  with  an  equal  volume  of  a  mineral 
phosphate  solution,  the  value  of  which  had  been  previously 
determined  by  both  the  molybdate  and  citrate  methods.  The  50 
cubic  centimeters  thus  obtained  represented  a  quarter  of  a  gram 
each  of  the  cake-meal  and  mineral  phosphates.  The  filtration 
followed  1 8  hours  after  adding  the  magnesia  mixture.  The 
following  data  show  the  results  of  the  determinations : 


I 

Per  cent. 
PjO5  in  mineral 
phosphate. 

15  17 

Per  c«nt. 
P2Os  in  organic 
sample. 

2.52 

Per  cent. 
PoO5  found  in 
"mixture. 

17.90 

Per  cent. 
PjOs  in  organic 
sample. 

2.51 

11  68 

oj 
2.52 

.    ir  17 

2  52 

O      *  v"-/ 

2-45 

A... 

.    11.58 

2.52 

14.20 

2.62 

content  of  P2O5  in  organic  sample 2.53 

It  is  thus  demonstrated  that  the  citrate  method  can  be  applied 
with  safety  even  to  the  determination  of  the  phosphoric  acid  in 
organic  compounds  where  the  quantity  present  is  less  than  three 
per  cent.  It  is  further  shown  that  solutions  of  mineral  phosphates 
varying  in  content  of  phosphoric  acid  from  15  to  32  per  cent, 
may  be  safely  used  for  increasing  the  content  of  that  acid  to 
the  proper  degree  for  complete  precipitation.  In  cases  where 
organic  matters  are  present  they  should  be  destroyed  by  moist 
combustion  with  sulfuric  acid,  as  in  the  determination  of  nitrogen 
to  be  described  in  the  next  part. 

98.  Direct  Precipitation  of  the  Citrate-Soluble  Phosphoric  Acid. 
— The  direct  determination  of  the  citrate-soluble  phosphoric  acid 
by  effecting  the  precipitation  by  means  of  magnesia  mixture  in 
the  solution  obtained  from  the  ammonium  citrate  digestion,  has 
been  practiced  for  many  years  by  numbers  of  European  chemists, 
and  the  process  has  even  obtained  a  place  in  the  official  methods 
of  some  European  countries.  Various  objections  have  been  urged, 
however,  against  the  general  employment  of  this  method  in  fer- 
tilizer analysis  on  account  of  the  inaccuracies  in  the  results  ob- 
tained in  certain  cases,  and  it  has,  therefore,  been  used  to  but  a 
very  limited  extent  in  this  country.  Since  it  is  impracticable  to 
effect  the  precipitation  with  ammonium  molybdate  in  the  presence 
of  citric  acid  the  previous  elimination  or  destruction  of  this  sub- 


CITRATE-SOLUBLE    PHOSPHORIC    ACID  IOJ 

stance  has  been  recognized  as  essential  to  the  execution  of  a 
process  involving  the  separation  of  the  phosphoric  acid  as  phos- 
phomolybdate. 

It  is  evident  from  the  data  cited  in  the  preceding  paragraph, 
that  great  accuracy  may  be  secured  in  this  process  by  adding  a 
sufficient  quantity  of  a  solution  of  a  mineral  phosphate  and  pro- 
ceeding by  the  citrate  method. 

Ross  has  also  proposed  to  estimate  the  acid  soluble  in  ammonium 
citrate  directly  by  first  destroying  the  organic  matter  by  moist 
combustion  with  sulfuric  acid.76  He  recommends  the  following 
process : 

After  completion  of  the  30  minutes'  digestion  of  the  sample 
with  citrate  solution,  25  cubic  centimeters  are  filtered  at  once  into 
a  dry  vessel.  If  the  liquid  be  filtered  directly  into  a  dry  burette, 
25  cubic  centimeters  can  be  readily  transferred  to  another  vessel 
without  dilution.  After  cooling,  run  25  cubic  centimeters  of  the 
solution  into  a  digestion  flask  of  250-300  cubic  centimeters  capac- 
ity, add  about  15  cubic  centimeters  of  concentrated  sulfuric  acid 
and  place  the  flask  on  a  piece  of  wire  gauze  over  a  moderately 
brisk  flame ;  in  about  eight  minutes  the  contents  of  the  flask  com- 
mence to  darken  and  foaming  begins ;  but  this  will  occasion  no 
trouble,  if  an  extremely  high  or  a  very  low  flame  be  avoided. 
In  about  12  minutes  the  foaming  ceases  and  the  liquid  in  the 
flask  appears  quite  black ;  about  one  gram  of  mercuric  oxid  is  now 
added  and  the  digestion  is  continued  over  a  brisk  flame.  The 
operation  can  be  completed  in  less  than  half  an  hour  with  ease, 
and  in  many  cases,  25  minutes.  After  cooling,  the  contents  of  the 
flask  are  washed  into  a  beaker,  ammonia  is  added  in  slight  excess, 
the  solution  is  acidified  with  nitric  acid,  and  after  the  addition  of 
15  grams  of  ammonium  nitrate,  the  process  is  conducted  as 
usual. 

In  case  as  large  an  aliquot  as  50  cubic  centimeters  of  the 
original  filtrate  be  used,  10  cubic  centimeters  of  sulfuric  acid  are 
added,  and  the  digestion  is  conducted  in  a  flask  of  300-500  cubic 
centimeters  capacity ;  after  the  liquid  has  blackened  and  foam- 
ing has  progressed  to  a  considerable  extent,  the  flask  is  removed 
76  Division  of  Chemistry,  Bulletin  38,  1893  :  16. 


108  AGRICULTURAL   ANALYSIS 

from  the  flame,  15  cubic  centimeters  more  of  sulfuric  acid  are 
added,  and  the  flask  and  contents  are  heated  at  a  moderate  tem- 
perature for  two  or  three  minutes;  the  mercuric  oxid  is  then 
added  and  the  operation  completed  as  before  described. 

Following  are  some  of  the  advantages  offered  by  the  method 
described : 

(i)  It  dispenses  with  the  necessity  of  the  frequently  tedious 
operation  of  bringing  upon  the  filter  and  washing  the  residue 
from  the  ammonium  citrate  digestion,  while  the  ignition  of  this 
residue  together  with  the  subsequent  digestion  with  acid  and 
filtration  are  also  avoided. 

(2)  It  affords  a  means  for  the  direct  estimation  of  that  form  of 
phosphoric  acid  which,  together  with  the  water-soluble,  consti- 
tutes the  available  phosphoric  acid,  thus  enabling  the  latter  to 
be  determined  by  making  only  two  estimations. 

(3)  In  connection  with  the  advantages  above  mentioned  it 
permits  of  a  considerable  saving  of  time  as  well  as  of  labor 
required  in  manipulation. 

In  addition  to  the  tests  with  mercuric  oxid,  both  potassium 
nitrate  and  potassium  sulfate  are  used  in  the  digestion  to  facil- 
itate oxidation.  With  the  former,  several  additions  of  the  salt 
are  necessary  to  secure  a  satisfactory  digestion,  and  even  then 
the  time  required  is  longer  than  with  the  mercury  or  mercuric 
oxid  digestion.  With  potassium  sulfate,  the  excessive  foaming 
which  takes  place  interferes  greatly  with  the  execution  of  the 
digestion  process. 

99.  Determination  of  Phosphoric  Acid  with  Preliminary  Pre- 
cipitation as  Stannic  Phosphate. — This  method  once  much  in  use 
and  highly  recommended,  is  now  almost  unknown  among  the  pro- 
cesses of  fertilizer  control.  It  was  first  proposed  by  Reynoso  and 
modified  by  Girard,  and  rests  on  the  precipitation  of  the  phos- 
phoric acid  in  a  nitric  acid  solution  by  means  of  metallic  tin.77 
The  stannic  acid  formed  by  the  oxidation  of  the  tin  unites  with 
the  phosphoric  acid  held  in  a  free  state  by  the  nitric  acid.  The 
precipitation  of  the  phosphoric  acid  is  said  to  be  complete,  and 
considerable  quantities  of  any  iron  or  alumina  which  may  be  pre- 
77  Comptes  rendus,  1862,  54  :  468. 


DETERMINATION   OF   PHOSPHORIC   ACID  109 

sent  are  carried  down  with  it.  A  trace  of  phosphoric  acid  has 
been  found  in  the  iron  and  alumina  subsequently  separated  from 
the  solution.  The  precipitate  obtained  is  dissolved  in  aqua  regia, 
made  strongly  ammoniacal  and  an  excess  of  ammonium  hydrosul- 
fid  added.  The  iron  and  the  alumina  are  thrown  out  by  this 
treatment.  After  standing  for  an  hour  the  precipitate  is  separat- 
ed by  filtration,  washed  with  the  ammonium  sulfid  to  remove 
the  last  traces  of  tin  and  the  phosphoric  acid  is  separated  from 
its  filtrate  as  ammonio-magnesium  salt.  Following  is  the  second 
method  of  conducting  the  analysis  as  described  by  Crookes:78 

The  phosphate  should  be  dissolved  in  nitric  acid,  and  any 
chlorin  present  be  expelled  by  repeated  evaporations  with  the 
solvent.  Finally,  to  the  evaporated  mass  the  strongest  nitric 
acid  is  added.  Pure  tin  foil  is  added  and  heat  applied.  The  phos- 
phoric acid  is  precipitated  by  the  stannic  acid  formed.  The 
quantity  of  tin  used  should  be  from  four  to  five  times  as  great  as 
that  of  the  phosphoric  acid  present.  The  preliminary  heating 
is  indispensable,  since  in  the  cold  the  metal  is  apt  to  become  pas- 
sive in  which  state  it  resists  the  action  of  the  acid. 

The  precipitate  is  collected  on  a  filter,  washed  and  dissolved 
in  caustic  potash.  The  solution  is  saturated  with  hydrogen  sul- 
fid, and  on  adding  acetic  acid  in  slight  excess  the  tin  sulfid  is 
separated  and  removed  by  filtration.  The  whole  of  the  phos- 
phoric acid,  supposed  to  be  almost  free  of  tin,  is  now  found  in 
the  filtrate.  The  filtrate  is  concentrated  to  small  bulk  and  any 
tin  sulfid  present  separated  by  filtering,  and  the  phosphoric  acid 
finally  removed  from  the  ammoniacal  filtrate  by  precipitation 
with  magnesia  mixture.  The  chief  difficulties  of  this  method 
are  to  be  found,  on  the  one  hand,  in  the  retention  of  some  of  the 
phosphoric  acid  by  the  iron  and  alumina  which  may  be  present, 
and  on  the  other,  in  the  presence  of  some  tin  in  the  final  mag- 
nesium pyrophosphate.  If  the  tin  be  all  removed  as  sulfid,  the 
latter  source  of  error  will  be  avoided.  It  is  difficult  to  secure  pure 
metallic  tin,  and  this  is  another  disturbing  element  in  the  process. 

78  Select  Methods  in  Chemical  Analysis,  4th  Edition,  1905  :  497. 


Oil  AGRICULTURAL  ANALYSIS 

It  can  not  be  recommended  for  the  work  which  agricultural  an- 
alysts are  usually  called  on  to  perform.78 

100.  Phosphoric  Acid  Soluble  in  Ammonium  Citrate. — There  is 
no  other  point  connected  with  the  determination  of  phosphoric 
acid  which  has  excited  so  much  discussion  and  about  which 
there  is  such  difference  of  opinion  as  the  solubility  of  phosphates 
in  ammonium  citrate.  It  was  clearly  established  by  Huston,  in 
1882,  that  the  ammonium  citrate,  as  used  in  fertilizer  analysis, 
would  attack  normal  tricalcium  phosphate  as  it  exists  in  bones.80 

In  a  raw  bone,  finely  ground,  containing  20.28  per  cent,  of  phos- 
phoric acid,  the  following  quantities  are  found  to  be  soluble  in  a 
neutral  ammonium  citrate  solution  of  1 .09  specific  gravity : — 

Time  of  digestion,  thirty  minutes. 

Temperature 30°  40°  50°  60° 

Per  cent.  P2O5  dissolved 2.76  4.01  3.39  5.88 

From  this  it  appears  that  the  quantity  of  acid  dissolved  in- 
creases with  the  temperature  of  digestion  with  the  exception 
of  the  number  obtained  at  50°.  When  the  time  of  digestion  is 
increased  there  is  also  found  a  progressive  increase  in  the  amount 
of  acid  passing  into  solution.  At  40°  for  45  minutes  the  per 
cent,  dissolved  is  4.97,  and  40°  for  one  hour,  5.92.  These  early 
determinations  had  the  effect  of  calling  attention  to  the  thoroughly 
empirical  process  which  was  in  use,  in  many  modified  forms,  by 
agricultural  chemists  the  world  over  for  determining  so-called 
reverted  phosphoric  acid  in  fertilizers.  Since  the  publication  of 
the  paper  above  named  many  investigations  have  been  undertaken 
by  Huston  and  others  relating  to  this  matter.81 

The  conditions  of  solution  studied  embraced  the  influence  of 
time,  temperature,  kind  and  quantity  of  material,  and  acidity  and 

n  Fresenius,  Quantitative  Analysis,  Cohn's  Translation  of  Sixth  German 
Edition,  1904,  1  :  450. 

80  Wiley,    32nd    Annual     Report    of    the     Indiana    State     Board    of 
Agriculture,  1882  :  225. 

81  American  Chemical  Journal,  1884-5,  6  :  i. 

Proceedings  of  the   Convention  of  Agricultural   Chemists,  Atlanta 
Meeting,  1884,  Edited  by  C.  W.  Dabney,  Secretary  :  23,  28,  38,  45. 
Division  of  Chemistry,  Bulletin  7,  1885  :  18. 
Division  of  Chemistry,  Bulletin  28,  1890  :  171. 
Division  of  Chemistry,  Bulletin  31,  1891  :  99. 


PHOSPHORIC   ACID   SOLUBLE   IN   AMMONIUM   CITRATE      III 

alkalinity  of  the  solvent  on  the  amount  of  phosphoric  acid  dis- 
solved. The  materials  subjected  to  experiment  represented  a  wide 
range  of  substances  used  as,  or  entering  into  the  composition  of, 
phosphatic  fertilizers  such  as  bone  meal,  steamed  bone,  orchilla 
guano,  navassa  rock,  navassa  superphosphate,  Florida  soft  rock, 
precipitated  calcium  phosphate,  Pamunky  phosphate,  calcined 
redonda,  South  Carolina  rock,  apatite,  grand  connetable,  acid  na- 
vassa, South  Carolina  phosphate,  dissolved  bone-black,  and  cotton- 
seed meal. 

The  time  of  digestion  extended  from  half  an  hour  to  10  hours, 
and  in  general  the  quantity  of  phosphoric  acid  dissolved  by  the 
ammonium  citrate  solution  increased  as  the  time  of  digestion  was 
prolonged. 

The  digestions  were  made  at  temperatures  ranging  from  30* 
to  85°.  In  general,  the  quantity  of  phosphoric  acid  dissolved  in- 
creased with  the  temperature. 

The  quantity  of  sample  used  in  its  relations  to  the  volume  of 
the  solvent  was  also  studied.  The  percentage  of  the  total  acid 
dissolved  increases  very  rapidly  as  the  weight  of  the  sample 
diminishes. 

The  addition  of  citric  acid  to  the  neutral  ammonium  citrate 
increases  its  solvent  power.  On  the  other  hand,  the  addition  of 
ammonia  to  the  neutral  solution  of  ammonium  citrate  diminishes 
its  solvent  power. 

The  finer  the  state  of  subdivision  of  the  sample  the  more  effi- 
ciently the  solvent  acts. 

An  examination  of  the  original  paper  of  Fresenius,  Neubauer, 
and  Luck,  on  whose  researches  the  citrate  method  is  based,  shows 
that  the  temperature  conditions  are  not  carefully  controlled.82  An 
attempt  has  been  made  to  summarize  in  the  above  conclusions, 
work  made  under  well  defined  conditions  which  illustrate  the 
various  points  under  consideration.  While  each  authority  of  value 
upon  the  subject  is  represented,  no  attempt  has  been  made  to  dis- 
cuss all  the  work  done  by  any  of  them.  One  element  that  seems  to 
have  been  generally  overlooked  in  discussing  the  problem  is  that 
nearly  all  results  have  been  obtained  from  a  one-half  hour  treat- 
82  Zeitschrift  fur  analytische  Chemie,  1871,  10  :  133. 


112  AGRICULTURAL   ANALYSIS 

ment  of  the  material.  This  means  simply  the  study  of  an  incom- 
plete reaction,  and  one  which  is  interrupted  while  the  solution  is 
very  rapidly  going  on.  This,  of  course,  is  only  clearly  brought 
out  by  comparison  of  long-time  and  short-time  work  in  the 
various  tables.  In  the  opinion  of  Huston,  much  more  work 
will  have  to  be  done  before  it  can  be  assumed  that  we  have  any 
very  clear  knowledge  of  this  subject,  and  probably  the  conclusion 
will  be  that  all  kinds  of  materials  can  not  be  examined  by  the 
same  method.  The  fact  that  half  a  gram  of  dicalcium  phosphate 
is  instantly  soluble  in  100  cubic  centimeters  of  citrate  solution, 
at  ordinary  temperatures,  while  an  equal  amount  of  iron  and 
aluminum  phosphate  is  acted  upon  very  slowly  at  ordinary  tem- 
peratures will  probably  have  to  be  taken  into  consideration,  as 
well  as  the  fact  that  dicalcium  phosphate  is  less  soluble  in  hot 
solutions  of  ammonium  citrate  than  it  is  in  cold  solutions,  while 
the  reverse  is  true  of  the  precipitated  iron  and  aluminum  phos- 
phate. 

At  present  the  only  conclusion  that  can  be  safely  drawn  from 
the  work  is  that  it  would  be  unsafe  to  make  any  generalization 
upon  the  subject  until  more  facts  are  at  hand,  except  that  the 
methods  generally  in  use  are  unscientific  and  unsatisfactory.  As 
the  work  progresses,  new  features  present  themselves,  and  in  such 
a  way  as  to  show  that  they  must  be  given  careful  consideration 
before  drawing  any  final  conclusions  in  the  matter.  At  best,  it 
must  be  confessed  that  the  action  of  a  neutral  ammonium  citrate 
solution  on  the  various  forms  of  phosphates  entering  into  the 
composition  of  commercial  fertilizers  is  a  practically  continuous 
process,  varying  in  speed  with  changing  conditions  of  tempera- 
ture, time,  relation  of  quantity  of  sample  to  volume  of  substance, 
and  the  fineness  of  subdivision  of  the  sample.  Concordant  re- 
sults can  therefore  only  be  obtained  by  observing  fixed  conditions 
of  work. 

101.  Arbitrary  Determination  of  Reverted  Phosphoric  Acid.. — 
The  so-called  reverted  phosphoric  acid,  that  is,  the  acid  insoluble 
in  water  and  soluble  in  a  solution  of  ammonium  citrate,  is  the  most 
annoying  constituent  of  commercial  fertilizers  from  the  point 
of  view  of  the  scientific  analyst.  A  review  of  all  the  standard 


DETERMINATION   OF   REVERTED   PHOSPHORIC   ACID         113 

methods,  which  have  been  given  in  the  preceding  pages,  for  its 
determination  must  convince  every  careful  observer  that,  as  a 
rule,  each  process  is  based  on  arbitrary  standards,  and  can  give 
only  concordant  results  when  carried  out  under  strictly  unvary- 
ing conditions.  For  this  reason  there  can  be  no  just  comparison 
between  the  results  obtained  by  different  methods,  which  vary 
from  each  other  only  in  slight  particulars.  When,  on  the  other 
hand,  the  processes  are  radically  different,  the  deviations  in  data 
become  more  pronounced. 

In  such  a  condition  of  affairs  the  analyst  is  left  to  choose 
between  methods.  He  must  be  guided  in  his  choice  not  only  by 
what  seems  to  be  the  most  scientific  and  accurate  process,  but 
also,  to  a  certain  extent,  by  the  general  practice  of  his  professional 
brethren.  For  this  country,  therefore,  it  is  strongly  urged  that 
the  methods  adopted  by  the  Association  of  Official  Agricultural 
Chemists  be  followed  in  every  detail. 

By  the  phrase  "  reverted  phosphoric  acid "  was  originally 
meant  an  acid  once  soluble  in  water,  as  CaH4(PO4)2,  and  after- 
wards changed  to  a  form  insoluble  in  water,  but  soluble  in 
ammonium  citrate  as  Ca2H2(PO4)2.  But  in  practice  this  has  never 
been  the  true  signification  of  the  term.  In  the  manufacture  of 
acid-  and  superphosphates  there  is  formed,  more  or  less  of  the 
dicalcium  phosphate,  either  directly  or  after  a  time,  and  this  salt 
which,  in  no  sense  can  be  called  reverted,  is  entirely  soluble  in 
r.mrnonium  citrate.  The  iron  and  aluminum  phosphates  are  also, 
to  a  certain  degree,  soluble  in  the  same  reagent.  When  an  acid 
phosphate,  containing  various  forms  of  calcium  phosphate,  is 
applied  to  a  soil  containing  iron  and  alumina,  the  soluble  parts 
of  the  compound  tend  to  become  fixed  by  union  with  those  bases, 
or  by  precipitation  as  Ca2H2(PO4).,.  But  it  is  not  alone  reverted 
phosphate  formed  in  this  way,  which  the  analyst  is  called  on  to 
determine  in  a  fertilizer,  although  he  may  have  occasion  to  treat 
it  in  soil  analysis. 

The  expression  "reverted  phosphoric  acid,"  therefore,  in  prac- 
tice not  only  includes  a  dicalcium  phosphate,  which  once  may 
have  been  the  monocalcium  salt,  but  also  all  of  that  salt  origi- 
nally existing  in  the  superphosphate,  and  formed  directly  during 


114  AGRICULTURAL,   ANALYSIS 

its  manufacture,  as  well  as  any  iron  and  aluminum  phosphates 
present  which  are  soluble  in  ammonium  citrate.  It  also  includes 
any  tricalcium  phosphate,  such  as  that  existing  in  bones,  which 
may  pass  into  solution  under  the  influence  of  ammonium  citrate. 
The  expression  "citrate-soluble"  is,  therefore,  to  be  preferred  to 
"reverted"  phosphoric  acid. 

102.  Theory  of  Reversion. — In  the  reversion  of  the  phosphoric 
acid  in  superphosphates  the  iron  plays  a  far  more  important  role 
than  the  aluminum  sulfate.  It  was  formerly  supposed  that  the 
reversion  took  place  as  indicated  in  the  following  formula: 
2CaH4(PO4)2+Fe2O3=2(CaHPO4.FePO4)+3H2O,  while  Wag- 
ner affirms  that  the  reverted  acid  compounds  consist  of  vary- 
ing quantities  of  ferric  oxid,  aluminum  oxid,  phosphorus  pent- 
oxid,  and  calcium  oxid,  in  various  states  of  combination.83 
The  more  probable  reaction  is  the  following:  3CaH4(PO4)2-f- 
Fe2  ( S04 )  3+4H20=2  ( FePO4,2H3PO4,2H2O )  -f-3CaSO4.  This 
reaction  can  be  demonstrated  by  adding  to  a  superphosphate 
solution  one  of  a  ferric  salt.  In  addition  to  free  phosphoric 
acid,  iron  phosphate  is  separated,  which  gradually  passes  into 
an  insoluble  form  by  the  abstraction  of  water  due  to  the  crystal- 
lization of  the  gypsum.  The  alumina  present  in  a  superphos- 
phate seems  to  have  no  direct  influence  on  the  process  of  re- 
version. Its  phosphate  salt  is  not  acted  on  by  the  acid  calcium 
phosphate.  Even  when  a  superphosphate  solution  is  treated  with 
alum  no  precipitation  is  produced,  except  on  warming,  and  this 
disappears  when  the  mass  is  again  cold. 

It  is  therefore  not  necessary  in  the  process  of  manufacture 
to  separate  the  alumina  by  digestion  with  a  hot  soda-lye  before 
treating  the  mass  with  sulfuric  acid. 

In  order  to  avoid  the  reversion  of  the  phosphoric  acid  several 
plans  have  been  proposed.  One  of  the  best  is  to  use  a  little 
excess  of  sulfuric  acid  in  the  manufacture.  This  tends  to  hold 
the  phosphoric  acid  in  soluble  form,  but  is  objectionable  on 
account  of  drying,  handling,  and  shipping  the  fertilizer.  During 
the  digestion,  moreover,  it  is  important  that  the  temperature  do 
not  rise  above  120°.  Another  method  consists  in  adding  to  the 
M  Lehrbuch  der  Diingerfabrikation. 


DIGESTION    APPARATUS   FOR    REVERTED    PHOSPHATES     115 

dissolved  rock  a  quantity  of  common  salt  chemically  equivalent 
to  its  iron  content.  Ammonium  sulfate  also  helps  to  hold  the 
phosphoric  acid  water-soluble.  Reversion  of  the  phosphoric  acid 
is  quite  certain  to  take  place  in  those  products  where  the  solvent 
action  of  the  sulfuric  acid  has  not  been  complete.84  Especially 
is  this  the  case  when  there  are  still  substances  present  which  can 
be  attacked  by  the  acid  calcium  phosphate.  This  action  is  illus- 
trated by  the  following  equation : 

CaH4(PO4)2+Ca3(PO4)2-f8H2O=4CaHPO4(H2O)2. 

In  this  case  the  undissolved  tricalcium  phosphate  is  attacked  by 
the  acid  monocalcium  phosphate  with  the  production  of  a  com- 
pound insoluble  in  water. 

103.  Influence  of  Movement. — The  influence  of  time  and  tem- 
perature of  digestion,  and  of  variations  in  the  composition  of 
the  ammonium  citrate  on  the  quantity  of  phosphoric  acid  dis- 
solved by  that  reagent,  has  been  pointed  out.     Of  great  impor- 
tance also  in  the  process  is  the  character  of  the  movement  to 
which  the  materials   are  subjected   during  the   digestion.     For 
this  reason  various  mechanical  devices  have  been  constructed  to 
secure  uniformity  of  solution.     Inasmuch  as  the  temperature  fac- 
tor must  also  be  faithfully  observed,  the  best  of  these  devices  are 
so  arranged  as  to  admit  of  a  uniform  motion  within  a  bath  of 
water  kept  at  the  desired  temperature  which,  by  the  association 
method,  is  65°. 

104.  Digestion  Apparatus  for  Eeverted  Phosphates. — The  diges- 
tion apparatus  used  by  Huston  consists  of  two  wheels  25  centi- 
meters in  diameter,  mounted  on  the  same  axis,  having  a  clear 
space  of  four  and  one-half  centimeters  between  them.85     In  the 
periphery  of  each  wheel  are  cut  12  notches,  which  are  to  re- 
ceive the  posts  bearing  the  rings  through  which  the  necks  of  the 
flasks  pass.  The  posts  are  held  in  place  by  nuts  which  are  screwed 
down  on  the  faces  of  the  wheel.     Should  it  become  necessary  to 

84  Riimpler,  Kaufliche  Dungestoffe  und  ihre  Anwendung,  4th  Edition, 
1897  :  85. 

85  Indiana  Agricultural  Experiment  Station,  Bulletin  54,  1895  :  4. 


Il6  AGRICULTURAL   ANALYSIS 

take  the  apparatus  apart,  it  is  only  necessary  to  loosen  the  nuts 
and  the  set  screw  holding  one  wheel  to  the  shaft  and  all  the  parts 
can  at  once  be  removed.  The  posts  extend  10  centimeters  beyond 
the  face  of  the  wheels,  and  the  rings  are  four  centimeters  in  inter- 
nal diameter.  Perforated  plates,  bearing  a  cross-bar,  and  held  in 
place  by  strong  spiral  springs  attached  to  the  plate  and  the  base  of 
the  posts  serve  to  hold  the  flasks  in  place.  Each  plate  has  a  number 
stenciled  through  it  for  convenience  in  identifying  the  flasks 
when  it  is  time  to  remove  them.  Attached  to  the  outside  of  each 
post,  close  to  the  outer  end,  is  a  heavy  wire  which  passes  entirely 
around  the  apparatus,  serving  to  keep  the  plates  in  place  after 
they  are  removed  from  the  flasks. 

The  apparatus  is  mounted  on  a  substantial  framework,  36 
centimeters  high  and  30  centimeters  wide  at  the  base.  The  space 
in  which  the  wheel  revolves  is  14  centimeters  wide.  The  base  bars 
connecting  the  two  sides  are  extended  seven  centimeters  beyond 
one  side,  and  serve  for  the  attachment  of  lateral  bracing.  At  the 
top  of  the  framework,  at  one  side,  is  attached  a  heavy  bar  45  centi- 
meters long,  which  serves  to  carry  the  cog  gearing  which  trans- 
mits the  power.  The  upright  shaft  carries  a  cone  pulley  to  pro- 
vide for  varying  the  speed.  The  usual  speed  is  two  revolutions 
a  minute  for  the  wheel  carrying  the  flasks.  The  entire  apparatus 
is  made  of  brass.  The  details  of  construction  are  shown  in  Fig. 
6.  Round-bottomed  flasks  are  used,  and  the  rubber  stoppers  are 
held  in  place  by  tying  or  a  special  clamp  shown  at  the  lower 
right-hand  corner  of  the  figure. 

When  high  temperatures  are  used,  the  plates  and  flasks  are 
handled  by  the  hooks  shown  at  the  left  and  right-hand  upper 
corners  of  the  figure. 

When  any  other  than  room  temperature  is  desired,  the  whole 
apparatus  is  immersed  in  water  contained  in  the  large  galvanized 
tank  forming  the  back-ground  of  the  figure.  The  tank  is  75 
centimeters  long,  75  centimeters  high,  and  30  centimeters  wide. 
At  one  end,  near  the  top,  is  an  extension  to  provide  space  for 
heating  the  fluid  in  the  flasks  before  introducing  the  solid,  in 
such  cases  as  may  be  desired. 


Fig.  6.    Huston's  Agitating  Machine. 


COMPARISON   OP   RESULTS 


1  I  7 


The  apparatus  is  held  in  place  by  angle  irons  soldered  to  the 
bottom  of  the  tank  and  a  brace  resting  against  the  upright  bar 
bearing  the  gear-wheels. 

The  water  in  the  tank  is  heated  by  injecting  steam,  or  by 
burners  under  the  tank.  As  the  tank  holds  about  300  pounds 
of  water  it  is  not  subject  to  sudden  changes  of  temperature, 
and  little  trouble  has  been  experienced  in  raising  and  lowering 
the  temperature  of  the  water  and  maintaining  it  at  any  desired 
temperature. 

An  electric  motor,  or  a  small  water-motor  with  only  a  very 
moderate  head  of  water,  will  furnish  ample  power. 

105.  Comparison  of  Results.  —  The  following  data  show  the  re- 
sults obtained  by  the  digester  as  compared  with  those  furnished  by 
the  official  method,  temperature  and  time  of  digestion  being  the 
same  in  each  instance. 

AMMONIUM  CITRATE  SOLUTION  ON  PHOSPHATES. 

Total 

Time 

of 
Substance.  treatment. 

{      Yt  hour 

1  " 

2  hours 
Steamed  bone,    ..................  -j    3^     " 

5 
lYt 


Marl, 


hours 


f      Yt  hour 
II         " 
Acidulated  bone,    ..........  ........  {    2      hours 


Bone,  ............................  Yi  hour 

Ammoniated  dissolved  bone,  ......  Yt 

Cottonseed-meal  and  castor  pomace,  ^ 

Phosphobone,  ............  .  ......  % 

In  comparing  duplicates,  the  results  from  the  use  of  the 
digester  are  found  to  be  subject  to  less  variation  than  those  from 
the  usual  method.  It  is  seen  that  in  many,  in  fact,  the  majority 


phos-        Removed 
phoric    by  official 
acid.         method. 
Per  cent.    Per  cent. 

Removed 
by 
digester. 
Per  cent. 

27.67 

10-59 
12.21 

14.  6r 
16.48 

M-52 
14.82 
17.56 
18.53 

17-94 
18.99 

19-73 

2O.22 
20.25 
21.18 

13-86 

4-43 
8.28 

4.11 
6.82 

10.34 

9-76 

i  r.oo 
11.80 
12.51 
12.58 

11.31 
11.83 
12.64 
13.00 

19.38 

12.09 

12  28 

12.47 

12.40 

1  2.  2O 

12.43 

•12.40 
12-43 

12.24 
12.26 

21.40 
18.22 

6.97 
9.28 

8.48 
10.63 

2.52 
16.55 

0.23 

025 

n8 


AGRICULTURAL   ANALYSIS 


of  cases,  the  quantity  of  phosphoric  acid  dissolved  is  markedly 
greater  than  by  the  methods  where  no  mechanical  stirring  is 
employed. 

1 06.  Huston's  Mechanical  Stirrer. — The  stirring  apparatus 
shown  in  Fig.  7  differs  from  those  which  have  heretofore  come 
into  use  in  requiring  but  a  single  belt  to  drive  all  the  stirring  rods, 
and  having  all  the  parts  protected  from  the  laboratory  fumes.88 
The  details  of  the  belt  system  are  shown  in  the  small  diagram  in 
the  lower  central  part  of  the  figure.  The  apparatus  is  mounted  on 
a  substantial  wooden  box,  200  centimeters  long,  30  centimeters 
high,  and  18  centimeters  wide.  The  driving  pulleys,  10  centi- 
meters in  diameter,  are  enclosed  in  the  upper  part  of  the  case. 
The  shafts  on  which  these  pulleys  are  mounted  extend  through 


Fig.  7.    Huston's  Mechanical  Stirrer. 

the  bottom  of  the  enclosing  box  and  carry  a  wooden  disk,  n 
centimeters  in  diameter,  to  prevent  particles  of  foreign  matter 
from  falling  into  the  beakers.  The  shafts  extend  two  centimeters 
below  these  disks,  and  to  the  end  of  the  shafts  the  bent  stirring 
rods  are  attached  by  rubber  tubing. 

The  board  forming  the  support  of  the  driving  pulleys  is  ex- 
tended two  centimeters  in  front  of  the  apparatus,  and  in  this 
extension  12  notches  are  cut,  in  which  are  held  the  corks  carry- 
ing the  tubes  which  contain  the  solution  to  be  used  in  precip- 
itating the  material  in  the  beakers. 

The  ends  of  these  tubes  are  drawn  out  to  a  fine  point  so  as  to 
deliver  the  liquid  at  the  rate  of  about  one  drop  per  second. 

The  front  of  the  apparatus  is  hinged  and  permits  the  whole  to 
be  closed  when  not  in  use,  or  during  the  precipitation. 

86  Indiana  Agricultural  Experiment  Station,  Bulletin  54,  1895  :  7. 


WATER   AND   CITRATE-SOLUBLE   PHOSPHORIC   ACID          1 19 

The  apparatus  has  proven  extremely  satisfactory  in  the  pre- 
cipitation of  ammonium  magnesium  phosphate.  The  precipi- 
tate is  very  crystalline,  and  where  the  stirring  is  continued  for 
some  minutes,  after  the  magnesia  solution  has  all  been  added, 
no  amorphous  precipitate  is  observed  on  longer  standing. 

107.  Precipitation  of  the  Water  and  Citrate-Soluble  Phosphoric 
Acid. — The  importance  of  rapid  precipitation  with  vigorous  stir- 
ring when  the  molybdate  solution  is  employed  has  also  been 
pointed  out  by  Ledoux  and  likewise  the  desirability  of  keeping 
the  temperature  low  (i6°).8T 

In  the  use  of  the  aqueous  and  citrate  extract  of  superphos- 
phates the  precipitation  is  conducted  as  follows : 

The  aqueous  or  citrate  extract,  or  both  combined,  is  made  up  to 
a  volume  of  250  cubic  centimeters,  or  each  is  made  up  to  that  vol- 
ume. A  part  of  the  solution  representing  0.2  gram  of  the  sample 
is  boiled  with  15  cubic  centimeters  of  strong  nitric  acid  of  1.4 
specific  gravity  for  five  minutes  to  convert  all  phosphoric  acid  in- 
to the  ortho  type.  After  cooling,  15  cubic  centimeters  of  am- 
monia of  0.92  specific  gravity  is  added,  leaving  the  mixture 
slightly  acid,  and  then  100  cubic  centimeters  of  the  molybdic  solu- 
tion, prepared  by  dissolving  150  grams  of  molybdic  acid  in  600 
cubic  centimeters  of  ammonia  of  0.96  density  and  pouring  the 
solution  into  1070  cubic  centimeters  of  nitric  acid  of  1.22  density. 
The  precipitation  is  made  with  vigorous  stirring,  best  by  a  me- 
chanical agitator,  for  30  minutes  at  a  temperature  not  exceed- 
ing 1 6°.  The  precipitate  is  perfectly  pure  and  the  phosphoric 
acid  may  be  determined  by  direct  weighing,  by  titration  or  by 
the  gravimetric  process. 

Many  of  the  above  precautions  were  previously  pointed  out 
by  Pellet  who  especially  called  attention  in  1889  to  tne  volumet- 
ric method  of  Thilo,  afterwards  developed  by  Pemberton  and  Kil- 
gore.88 

87  Bulletin  de  1' Association  beige  des  Chimistes,  1901,  15  :  125. 

88  Annales  de  Chimie  analytique,  1900,  5  :  244;  1901,  6  :  248. 
Bulletin  de  1' Association  des  Chimistes  de  Sucrerie  et  de  Distillerie, 

1893-94,  11  :  152;  1896-97,  14  :  423- 

Bulletin  de  1'Association  beige  des  Chimistes,  1888-89,  3  :  5r>  73- 


120  AGRICULTURAL   ANALYSIS 

108.  Veitch's  Method  for  Available  Phosphoric  Acid. — The  gen- 
eral acceptance  of  the  term  "available  acid''  as  including  both  the 
quantity  soluble  in  water  and  afterwards  the  additional  quantity 
soluble  in  ammonium  citrate  solution  has  led  to  the  suggestion 
that  a  single  determination  of  the  total  amount  of  the  dissolved 
acid  is,  for  practical  purposes,  fully  as  valuable  as  the  determina- 
tion of  the  two  extracts  separately.  The  usual  objection  to  the 
direct  determination  of  the  citrate-soluble  acid  with  the  preliminary 
separation  with  molybdate  solution  has  been  the  supposed  difficul- 
ty of  precipitating  the  phosphoric  acid  in  the  presence  of  a  large 
quantity  of  organic  matter,  viz.,  the  excess  of  the  citrate  used  in 
extracting  the  phosphoric  acid.     Experience  has  shown  that  ac- 
curate separation  can  be  secured,  even  in  the  presence  of  this 
form  of  organic  matter.     This  fact  led  Veitch  to  combine  the 
two  extracts  and  determine  the  so-called  available  acid  in  one 
operation.     This  process  is  as  follows  :so 

The  two  extracts,  viz.,  with  water  and  with  ammonium  citrate, 
are  placed  in  a  500  cubic  centimeter  flask  with  10  cubic  centi- 
meters of  nitric  acid  and  the  volume  completed  to  the  mark.  The 
phosphoric  acid  is  determined  in  aliquots  of  100  cubic  centimeters, 
whether  by  the  molybdate  or  direct  citrate  of  magnesia  method. 
The  precipitates  are  allowed  to  stand  18  hours  before  filtering. 

Comparisons  with  the  official  method  with  many  varieties  of 
phosphate  fertilizers  containing  from  five  to  15  per  cent,  of  avail- 
able acid,  show  close  agreement  when  the  molybdate  separation 
is  used,  while  by  direct  precipitation  with  citrate  of  magnesia, 
the  results  are  somewhat  lower. 

The  method  therefore  possesses  certain  advantages.  Only  one 
determination  is  required  instead  of  two,  and  ths  probable  error 
in  manipulation  is  reduced  one-half. 

109.  Availability  of  Phosphatic  Fertilizers. — There  is  perhaps 
no  one  question  more   frequently  put  to  analysts  by  practical 
farmers  than  the  one  relating  to  the  availability  of  fertilizing 
materials.     The  object  of  the  manufacturer  should  be  to  secure 
each  of  the  valuable  ingredients  of  his  goods  in  the  most  useful 
form.     The  ideal   form  in  which  phosphoric  acid  should  come 

89  Journal  of  the  American  Chemical  Society,  1899,  21  :  1090. 


AVAILABILITY   OF    PHOSPHATIC    FERTILIZERS  121 

to  the  soil  is  one  soluble  in  water.  Even  in  localities  where 
heavy  rains  may  abound,  there  is  not  much  danger  of  loss  of 
soluble  acid  by  percolation.  As  has  before  been  indicated,  the 
soluble  acid  tends  to  become  fixed  in  all  normal  soils  and  to  re- 
main in  a  state  accessible  to  the  rootlets  of  plants  and  yet  free 
from  the  danger  of  exhaustive  leaching.  For  this  reason  the 
water-soluble  acid  is  regarded  by  most  agronomists  as  more 
available  than  that  portion  insoluble  in  water,  yet  soluble  in 
ammonium  citrate. 

In  many  of  the  States  the  statutes,  or  custom,  prescribe  that 
only  the  water  and  citrate-soluble  acid  shall  be  reckoned  as  avail- 
able, the  insoluble  residue  being  allowed  no  place  in  the  esti- 
mates of  value.  In  many  instances  such  a  custom  may  lead  to 
considerable  error,  as  in  the  case  of  finely  ground  bones  and  some 
forms  of  soft  and  easily  decomposable  tricalcium  phosphates. 
There  are  also,  on  the  markets,  phosphates  composed  largely  of 
iron  and  aluminum  salts,  and  these  appear  to  have  an  available 
value,  often  in  excess  of  the  quantities  thereof  soluble  in  ammo- 
nium citrate. 

As  a  rule  the  apatites,  when  reduced  to  a  fine  powder  and  ap- 
plied to  the  soil  are  the  least  available  of  the  natural  phosphates. 
Finely  ground  bones  also  tend  to  give  up  their  phosphoric  acid 
with  a  considerable  degree  of  readiness  in  most  soils.  The  soft, 
finely  ground  phosphates,  especially  in  soils  rich  in  humus,  have 
an  agricultural  value,  almost  if  not  quite,  equal  to  a  similar 
amount  of  acid  in  the  acid  phosphates.  Natural  iron  and  alumi- 
num phosphates,  have  also,  as  a  rule,  a  high  degree  of  availability. 
Next  in  order  come  the  land  rock  and  pebble  phosphates  which, 
in  most  soils,  have  only  a  limited  availability.  In  each  case  the 
analyst  must  consider  all  the  factors  of  the  case  before  rendering 
a  decision.  Not  only  the  relative  solubility  of  the  different 
components  of  the  offered  fertilizer  in  different  menstrua  must  be 
taken  into  consideration,  but  also  the  character  of  the  soil  to  which 
it  is  to  be  applied,  the  time  of  application  and  the  crop  to  be  grown. 
By  a  diligent  study  of  these  conditions  the  analyst  may,  in  the  end, 
reach  an  accurate  judgment  of  the  merits  of  the  sample. 


122  AGRICULTURAL   ANALYSIS 

DIRECT  WEIGHING  OF  THE  PHOSPHOMOLYBDATE 
PRECIPITATE 

no.  Method  of  Hanamann. — It  has  already  been  stated  that 
many  attempts  have  been  made  to  determine  the  phosphoric  acid 
by  direct  weighing  as  well  as  by  titration,  as  in  the  Pemberton 
method.  The  point  of  prime  importance  in  such  a  direct  de- 
termination is  to  secure  an  ammonium  phosphomolybdate  mix- 
ture of  constant  composition.  Unless  this  can  be  done  no  direct 
method,  either  volumetric  or  gravimetric,  can  give  reliable  re- 
sults. Hanamann  proposes  to  secure  this  constant  composition 
by  varying  somewhat  the  composition  of  the  molybdate  mixture 
and  precipitating  the  phosphoric  acid  under  definite  conditions.90 
The  molybdate  solution  employed  is  prepared  as  follows : 

Molybdic  acid 100  grams. 

Ten  per  cent,  ammonia I  .o  liter. 

Nitric  acid  ( 1.246  sp.gr.) i .5  liters. 

The  precipitation  of  the  phosphoric  acid  is  conducted  in  the 
cold  with  constant  stirring.  It  is  complete  in  half  an  hour.  The 
ammonium  phosphomolybdate  is  washed  with  a  solution  of  ammo- 
nium nitrate  and  then  with  dilute  nitric  acid,  dried,  and  ignited 
at  less  than  a  red  heat.  It  should  then  have  a  bluish  black  color 
throughout.  Such  a  body  contains  4.018  per  cent,  of  phosphoric 
anhydrid. 

Twenty-five  cubic  centimeters  of  a  sodium  phosphate  solution 
containing  50  milligrams  of  phosphoric  acid  (P2O5),  treated  as 
above,  gave  a  bluish  black  precipitate  weighing  i  .249  grams,  which 
multiplied  by  0.04018,  equaled  50.018  milligrams  of  phosphorus 
pentoxid.  The  method  should  be  tried  on  phosphates  of  various 
kinds  and  contents  of  phosphorus  pentoxid  before  a  definite  judg- 
ment of  its  merits  is  formed.  The  method  is  applicable  to  phos- 
phates containing  a  large  percentage  of  phosphoric  acid  as  well  as 
to  compounds  having  very  little.  In  the  former  case  only  a  small 
aliquot  of  the  solution  is  subjected  to  precipitation,  while  in  the 
latter,  all  or  large  portions  are  used.  In  one  mixture  20  grams  of 
superphosphate  were  dissolved  in  one  liter  of  water  and  10  cubic 
centimeters  of  the  solution  poured  into  35  cubic  centimeters  of  the 
90  Chemiker-Zeitung,  1895,  19  :  553. 


METHOD   OF   LORENZ  123 

molybdate  mixture.  The  precipitate  obtained  weighed  0.9182 
gram,  showing  a  content  of  18.44  per  cent,  of  phosphoric  acid  in 
the  original  sample.  A  gravimetric  determination  yielded  the  same 
figure.  On  the  other  hand  a  sample  of  soil  which  showed  0.14 
per  cent,  of  phosphoric  acid  by  the  gravimetric  method,  was  ex- 
tracted with  HNO3  and  the  acid  extract  after  separation  of  the 
silica,  made  up  to  100  cubic  centimeters  and  the  whole  poured 
into  the  molybdate  mixture,  gave  a  content  of  0.14082  per  cent, 
of  phosphoric  acid. 

in.  Method  of  Lorenz. — The  various  methods  which  have  been 
proposed  for  the  direct  weighing  of  the  ammonium  molybdate  pre- 
cipitate of  phosphoric  acid,  have  been  made  the  subject  of  a 
practical  and  critical  study  by  Lorenz.91 

The  methods  of  Meineke,  Hanamann,  Woy  and  Hundes- 
hagen  are  compared  and  the  modifications  thereof  described. 

The  reagents  employed  by  Lorenz  are : 

1.  Ammonium  Molybdate. — This  reagent  is  prepared  by  pour- 
ing on  TOO  grams  of  pure  dry  ammonium  sulfate  in  a  glass  cylin- 
der of  two  liters  capacity,  one  liter  of  nitric  acid  of  1.36  specific 
gravity  at  15°  and  stirring  until  the  salt  is  dissolved.  In  a  liter  flask 
300  grams  of  purest  dry  ammonium  molybdate  are  dissolved  in 
hot  water,  cooled  to  about  20°  and  the  flask  filled  to  the  mark. 
The  contents  of  the  flask  are  poured  in  a  thin  stream  with  con- 
stant stirring  into  the  solution  of  ammonium  sulfate  in  nitric  acid. 
After  standing  for  at  least  48  hours,  the  solution  is  filtered  and 
stored  in  a  well  stoppered  bottle  kept  in  the  dark. 

2.  Nitric  acid  of  1.20  specific  gravity  at  15°. 

3.  A  mixture  of  sulfuric  and  nitric  acids  made  by  pouring  30 
cubic  centimeters  of  sulfuric  acid  of  1.84  specific  gravity  into  a 
liter  of  nitric  acid  of  1.20  specific  gravity. 

4.  A  two  per  cent,  aqueous  solution  of  pure  ammonium  nitrate. 

5.  Alcohol  of  from  90  to  95  per  cent,  strength. 

6.  Pure  ether. 

The  solution  of  the  phosphate  is  run  into  a  measuring  cylinder 
in  quantities  of  10,  15,  or  20  cubic  centimeters,  according  to  its 
strength  in  phosphoric  acid  and  the  volume  completed  to  50  cubic 
91  Die  landwirtschaftlichen  Versuchs-Stationen,  1901,  55  :  183. 


124  AGRICULTURAL   ANALYSIS 

centimeters  with  the  sulfuric-nitric  acid  mentioned  and  the 
mixture  placed  in  a  flask  of  250  cubic  centimeters  capacity.  The 
mixture  is  heated  and  there  is  added  thereto,  50  cubic  centimeters 
of  the  ammonium  molybdate  reagent.  After  standing  five  minutes 
the  mixture  is  stirred  vigorously  for  one  minute.  The  precipi- 
tate is  allowed  to  stand  for  from  three  to  18  hours  and  then 
separated  on  a  gooch  under  pressure,  not  through  asbestos  felt, 
but  as  recommended  by  Kilgore,  through  a  disk  of  ash- free  filter 
paper.  The  last  traces  of  the  yellow  precipitate  are  brought 
into  the  filter  and  washed  several  times  with  the  two  per  cent,  am- 
monia nitrate  solution.  The  precipitate  is  washed  three  times 
with  alcohol  and  as  many  times  with  ether,  sucking  the  filter  dry 
after  each  addition  of  the  washing  liquids.  When  washed  and 
dried  as  described  the  crucible  with  its  contents  is  placed  in  a 
partial  vacuum  desiccator  without  CaCl2  or  H2SO4  for  30  min- 
utes and  weighed.  The  ammonium  phosphomolybdate  prepared 
in  this  way  contains  3.295  per  cent,  of  P2O5. 

112.  Method  of  Woy. — The  direct  weighing  of  the  yellow  pre- 
cipitate in  the  determination  of  the  phosphoric  acid  in  slags  ex- 
tracted by  citric  acid  is  accomplished  by  Woy  in  the  following 
manner.02  • 

To  50  cubic  centimeters  of  the  solution  obtained  from  basic 
slags  by  treatment  with  a  two  per  cent,  citric  acid  solution  are  add- 
ed 30  cubic  centimeters  of  nitric  acid  of  1.153  specific  gravity,  and 
45  cubic  centimeters  of  ammonium  nitrate  solution  containing  340 
grams  of  the  salt  in  one  liter  of  water,  the  mixture  boiled  and  the 
phosphoric  acid  precipitated  by  the  addition  of  100  cubic  centi- 
meters of  a  boiling  aqueous  six  per  cent,  solution  of  ammonium 
molybdate.  After  standing  for  15  minutes  the  supernatant  liquid 
is  decanted,  the  precipitate  washed  with  50  cubic  centimeters  of 
a  solution  of  50  grams  of  ammonium  nitrate  and  40  cubic  centi- 
meters of  nitric  acid  in  one  liter  at  a  lukewarm  temperature  and 
then  collected  on  a  gooch  crucible,  dissolved  in  10  per  cent,  am- 
monia, 20  cubic  centimeters  of  ammonium  nitrate,  30  cubic  centi- 
meters of  water  and  one  cubic  centimeter  of  ammonium  molybdate 
added  to  the  filtrate,  boiled  and  the  yellow  precipitate  re-formed  by 
n  Chemiker-Zeitung,  1903,  27  :  279. 


BKRJU'S    MODIFICATION   OF    P.    NEUMANN'S    METHOD        125 

the  addition 'of  10  cubic  centimeters  of  nitric  acid.  The  precipi- 
tate is  collected  in  the  gooch  crucible,  washed  first  with  the  acid 
ammonium  nitrate  above  described,  then  with  alcohol  and  finally 
with  ether.  The  precipitate  is  ignited  at  first  gently  and  then  with 
a  medium  flame  until  the  surface  assumes  a  brilliant  crystalline 
deep  blue-black  appearance.  The  precipitate  is  represented  by 
the  formula  24Mo3P2O5,  and  contains  3.946  per  cent,  of  P2O5. 

Lorenz  regrets  that  the  German  experiment  stations  have  per- 
sisted in  retaining  the  direct  citrate  method  which  is  not  a  strict- 
ly scientific  proceeding,  but  asserts  that  his  own  method  of 
drying  the  yellow  precipitate  with  ether  without  ignition  con- 
sumes less  time  and  is  more  accurate  than  Woy's  modification  as 
given  above.92 

Sherman  and  Hyde  slightly  modify  the  processes  of  Woy 
and  have  been  able  to  obtain  results  with  this  method  on  some  20 
samples  of  fertilizers,  embracing  all  the  common  sources  of  phos- 
phoric acid,  which  agree  within  two-tenths  of  one  per  cent,  with 
results  obtained  by  the  molybdate-magnesia  method,  except  in  the 
case  of  a  phosphatic  slag,  in  which  the  variation  was  three-tenths 
per  cent.9*'95  As  the  precipitate  of  magnesium  pyrophosphate  con- 
tained iron,  the  results  by  the  gravimetric  method  were  probably 
high.  The  authors  use  a  three  per  cent,  solution  of  neutral  am- 
monium molybdate  and  add  from  five  to  eight  cubic  centimeters 
of  nitric  acid  to  the  neutral  phosphate  solution.  The  ammonium 
phosphomolybdate  is  washed  with  one  per  cent,  nitric  acid  until 
the  washings  amount  to  from  250  to  300  cubic  centimeters,  and 
ignited  at  a  low  heat  in  the  usual  way  without  dissolving  and  re- 
precipitating.  The  weight  of  the  phosphomolybdate  multiplied  by 
0.3949  gives  the  phosphoric  acid. 

113.  Berju's  Modification  of  P.  Neumann's  Method. — Berju  calls 
attention  to  the  fact  that  for  at  least  10  years  it  has  been  well 
known  that  phosphoric  acid  could  be  determined  with  great  exact- 
ness by  the  direct  weighing  of  the  phosphomolybdate  precipitate.90 
During  this  period  the  fact  has  been  repeatedly  verified.  In  his 

93  Chemiker-Zeitung,  1903,  27  :  495. 

94  Journal  of  the  American  Chemical  Society,  1900,  22  :  652. 

95  Chemiker-Zeitung,  1897,  21  :  441,  469. 

96  Journal  fiir  Laudwirtschaft,  1906,  54  :  31. 


126  '  AGRICULTURAL   ANALYSIS 

opinion,  none  of  the  methods  which  have  heretofore  been  pro- 
posed for  this  process  has  been  introduced  into  the  experiment 
stations  for  the  purpose  of  applying  it  to  the  estimation  of 
phosphoric  acid  in  fertilizers,  these  stations  having  continued  to 
follow  the  time-consuming  method  of  the  direct  precipitation  of 
the  phosphoric  acid  in  the  citrate  solutions,  although  this  method 
has  led  to  no  certain  results. 

The  method  of  P.  Neumann  is  preferred  as  the  process  for 
securing  the  phosphoric  acid,  because  it  requires  less  time  than 
the  other  methods  proposed  and  is  equally  exact.97  Berju,  there- 
fore, has  applied  the  principles  of  this  method  for  general  use  in 
the  investigation  of  fertilizers  containing  phosphoric  acid.  The 
accuracy  of  the  method  was  first  ascertained  by  its  application  to 
pure  sodium  phosphate  (Na2HPO4-)-i2H2O).  For  the  formula 
of  the  precipitate  he  adopts  that  proposed  by  Hundeshagen,  name- 
ly, i2MoO3PO4(NH4)3,  which  contains  3.78  per  cent.  P2O5.98 
The  method  of  procedure  is  the  following: 

Fifty  cubic  centimeters  of  the  phosphate  solution,  correspond- 
ing to  0.5  gram  of  sodium  phosphate,  are  treated  with  five  cubic 
centimeters  of  nitric  acid  of  1.2  specific  gravity,  and  with  75 
cubic  centimeters  of  ammonium  nitrate-molybdate  solution  pre- 
pared according  to  the  directions  of  Wagner-Stutzer,  for  the  pur- 
pose of  precipitating  the  phosphoric  acid.  The  mixture  is  stirred 
for  a  quarter  of  an  hour,  and  after  three-quarters  of  an  hour,  the 
precipitate  is  collected  upon  a  gooch  after  decanting  three  times 
with  about  30  cubic  centimeters  of  the  aqueous  solution  of  a  five 
per  cent,  ammonium  nitrate  solution  and  one  per  cent,  nitric  acid. 
The  filtrate  is  washed  six  times  and  the  precipitate  collected  as 
nearly  as  possible  upon  the  asbestos  felt. 

The  gooch  is  placed  in  a  somewhat  higher  porcelain  crucible 
and  the  precipitate  carefully  dried  over  a  free  flame,  the  tempera- 
ture being  gradually   raised  to  about   150°   to    180°    until   the 
ammonium  nitrate  is  completely  removed.     This  is  determined 
by  placing  a  watch  glass  upon  the  top  of  the  crucible  for  at  least 
half  a  minute  and  noticing  whether  any  deposit  is  found  thereon. 
"  Zeitschrift  fiir  analytische  Chemie,  1898,  37  :  303. 
96  Zeitschrift  fiir  analytische  Chemie,  1889,  28  :  141. 


•    THE   METHOD   OF    GRAFTIAU  1 27 

The  dried  precipitate  is  cooled  in  a  desiccator  and  weighed,  cov- 
ered with  a  watch  glass,  replaced  upon  the  burner,  converted  with 
a  stronger  heat  into  the  phosphomolybdate  anhydrid,  and  cooled 
and  weighed  as  before.  The  weight  of  this  precipitate  multiplied 
by  0.03946  gives  the  quantity  of  phosphoric  anhydrid  (P2O5). 

This  method  was  applied  to  superphosphates  and  basic  slags. 
In  the  case  of  basic  slags  it  was  found  that  the  results  by  the  fore- 
going method  were  accurate,  even  without  the  removal  of  the 
silicic  acid.  In  the  illustrations  given  it  appears  that  after  the  re- 
moval of  the  silicic  acid  there  was  found  19.30  per  cent,  of 
P2O5  by  the  direct  gravimetric  method,  while  by  the  weighing  of 
the  phosphomolybdate  precipitate  without  the  separation  of  the 
silica  in  two  cases  the  results  were  19.35  per  cent.  P2O5  and  19.26 
per  cent.  P2O5. 

In  a  determination  of  the  phosphoric  acid  soluble  in  a  citrate 
solution  of  basic  slag  by  the  direct  method,  there  was  found  14.7 
per  cent,  of  P2O5.  In  the  estimation  of  the  same  acid  after  the 
removal  of  the  silicic  acid  there  was  found  14.42  per  cent,  of 
P^Os  by  the  direct  method.  Without  the  removal  of  the  silicic 
acid  by  direct  weighing  of  the  phosphomolybdate  precipitate,  there 
was  found  14.43  Per  cent,  of  P2O5. 

The  general  conclusions  of  the  investigation  are : 

1.  The  methods  tried  for  the  estimation  of  the  phosphoric  acid 
in  fertilizers,  depending  upon  the  simplification  of  the  method  of 
•direct  precipitation  of  the  phosphoric  acid  as  MgNH4PO4,  give  al- 
most constantly  too  high  results. 

2.  The  estimation  of  phosphoric  acid  as  24MoO3P2O5,  accord- 
ing to  the  method  of  P.  Neumann,  gives  without  exception,  very 
exact  results,  and  the  use  of  the  different  solvents  for  the  phos- 
phoric acid  in  these  fertilizers,  as  well  as  the  presence  of  dissolved 
silicic  acid  in  the  hydrochloric  acid  and  citrate  solutions,  are 
without  influence  on  the  accuracy  of  the  results. 

Neumann's  method  is  at  least  more  simple  and  as  readily  ap- 
plicable as  the  common  method  for  estimating  phosphoric  acid  as 
Mg2P207. 

114.  The  Method  of  Graftiau. — Graftiau  has  proposed  some 
slight  modifications  of  the  method  of  determining  phosphoric 


128  AGRICULTURAL   ANALYSIS 

acid  by  weighing  the  ammonium  phosphomolybdate.  His  pro- 
cedure is  based  upon  a  solution  containing  a  proper  content 
of  nitric  acid,  of  ammonium  nitrate,  and  ammonium  citrate.  In 
such  a  solution  in  the  presence  of  an  excess  of  nitromolybdate 
ammonium,  the  phosphoric  acid  is  precipitated  rapidly  at  a  tem- 
perature of  about  70°.  The  precipitate  which  is  formed  is  pure 
and  it  is  dried  upon  filter  paper  without  decomposition  at  from 
105°  to  110°. 

The  method  is  used  particularly  in  Belgium,  where  by  an 
agreement  between  Belgium,  Holland,  and  the  Grand-Duchy  of 
Luxembourg,  only  two  methods  of  international  examination  of 
phosphates  are  permitted,  i.  e.}  the  direct  phosphomolybdate 
method  or  the  citro-magnesium  method.  The  method  by  the 
direct  weighing  of  phosphomolybdate  ammonium  is  therefore 
employed  only  as  a  means  of  control  in  these  countries. 

The  solutions  of  phosphates  are  prepared  according  to  the 
methods  prescribed  by  Kuss  for  the  analysis  of  fertilizing  ma- 
terials, cattle  feeds,  and  agricultural  products  for  the  Grand- 
Duchy  of  Luxembourg. 

The  acid  solutions  of  the  phosphates  and  basic  slags  are 
neutralized  by  ammonium  until  precipitation  commences.  The 
precipitate  is  redissolved  by  a  few  drops  of  nitric  acid  and  10 
cubic  centimeters  of  Petermann's  citrate  of  ammonium  solution 
added.  The  rest  of  the  process  is  the  same  as  that  employed 
where  citric  acid  or  ammonium  citrate  is  originally  used  for 
securing  a  solution  of  phosphates  soluble  therein. 

The  phosphoric  acid  having  been  thus  obtained  in  the  pres- 
ence of  a  solution  of  citrate  of  ammonium,  the  samples  are  treated 
as  follows: 

There  is  added  to  each  sample  containing  from  o.i  to  0.4 
gram  of  the  original  material,  according  to  its  richness  in  phos- 
phoric acid,  from  two  to  three  cubic  centimeters  of  concentrated 
citric  acid  from  10  to  15  cubic  centimeters  of  a  saturated  solu- 
tion of  ammonium  nitrate,  and  from  50  to  70  cubic  centimeters 
cf  water.  The  mixture  is  brought  to  the  boiling  point,  the  lamp 
removed,  and  there  is  added  from  60  to  100  cubic  centimeters 
(according  to  the  richness  of  the  sample)  of  ammonium  nitro- 


THE  METHOD  OF  PELLET  129 

molybdate,  containing  1 10  grams  of  molybdic  acid  dissolved  in 
400  cubic  centimeters  of  ammonium,  0.96  specific  gravity,  and 
the  solution  poured  slowly  into  1500  cubic  centimeters  of  nitric 
acid  of  i. 20  specific  gravity.  The  solution  is  cooled  to  about 
70°  and  allowed  to  rest  for  15  to  30  minutes.  The  precipitate 
sinks  very  rapidly,  leaving  a  perfectly  limpid  liquid.  The  greater 
part  of  the  liquid  is  siphoned  off  from  the  precipitate,  which 
is  afterwards  put  on  a  filter  and  washed  two  or  three  times  with 
water  containing  one  per  cent,  of  nitric  acid.  The  phospho- 
molybdate  of  ammonium  is  then  ready  to  be  dried. 

All  these  operations  require  very  little  time  because  the  pre- 
cipitate is  already  freed  from  its  mother  liquors  by  the  liquids 
which  have  been  used  for  washing  out  the  flasks. 

The  precipitate,  after  removing  from  the  funnel,  is  first 
placed  on  filter  paper,  with  care  so  as  not  to  break  the  paper,  and 
is  afterwards  transferred  to  the  drying  oven  where  it  is  dried 
for  two  hours  at  a  temperature  of  from  105°  to  110°,  as  above 
described. 

The  different  factors  which  should  be  used  for  calculating  the 
amount  of  phosphoric  acid  from  the  weight  of  phosphomolyb- 
date  vary  among  different  authors  and  the  factor  finally  selected 
is  0.0375,  which  is  only  slightly  different  from  that  proposed  by 
Boussingault,  i.  e.,  0.0373." 

115.  The  Method  of  Pellet. — In  1887  Pellet  proposed  to  the 
French  chemists  the  method  of  determining  phosphoric  acid  by 
weighing  ammonium  phosphomolybdate,  and  this  method  has 
been  employed  by  a  certain  number  of  chemists  in  France  since 
that  time.1  Pellet  is  led  to  believe  from  the  results  of  his  in- 
vestigations that,  when  precipitated  in  the  presence  of  a  citrate, 
ammonium  phosphomolybdate  is  of  constant  composition  and 
can  be  accurately  dried  and  weighed  on  tared  filter  paper.  The 
factor  used  for  calculating  the  phosphoric  anhydrid  is  O.O374.2 

™  Atti  del  VI  Congresso  inter uazionale  di  Chimica  applicata,  Roma, 
1906,  1  :  64. 

1  Atti  del  VI  Congresso  internazionale  di   Chimica  applicata,    Roma, 
1906,  1  :  321. 

2  Bulletin  del' Association  des  Chimistes  de  Sucrerie  et  de  Distillerie, 
1906-07,  24  :  525. 

5 


130  AGRICULTURAL  ANALYSIS 

116.  Cladding's    Modification. — Gladding    has    proposed    the 
following  modified  method  for  the  direct  determination  of  phos- 
phoric acid  by  weighing  the  yellow  precipitate:3     To  the  solu- 
tion of  phosphoric  acid  25  cubic  centimeters  of  strong  ammonia, 
0.90  specific  gravity,  is  added,  and  concentrated  nitric  acid  to 
acidity.     The  beaker  containing  the  solution  is  placed  in  a  water 
bath  at  50°  and  the  ordinary  molybdate  solution  added  at  the  rate 
of  three  drops  per  second  in  excess  and  with  constant  stirring. 
After   standing   10  minutes  the   solution   is   filtered   through  a 
weighed  filter  paper,  washed  six  times  with   i  :ioo  nitric  acid, 
once  with  water  and  dried  to  constant  weight  at  from  iO5°-io8° 
in  a  glycerol  or  salt  water  oven.     Careful  analysis  of  the  dried 
precipitate    led   to    the    formula:        24MoO3,P2O33(NH4)2O+ 
24MoO3,P2O6,2(NH4)2O.H2O+5H2O. 

Later  Gladding  recommended  that  the  yellow  precipitate  be 
given  two  final  washings  with  alcohol  to  facilitate  drying.4  This 
method  has  been  examined  by  the  Association  of  Official  Agri- 
cultural Chemists.  With  slight  modifications,  such  as  a  gooch 
crucible  with  a  paper  or  a'sbestos  felt  for  the  filtrations,  and  more 
thorough  washing  of  the  precipitate  with  water  (total  quantity 
from  100  to  300  cubic  centimeters)  it  has  been  found  to  give 
very  accurate  and  trustworthy  results.5 

VOLUMETRIC  DETERMINATION  OF  PHOSPHORIC  ACID. 

117.  Classification  of  Methods. — The  time  required  for  a  gravi- 
metric determination  of  phosphoric  acid  has  led  analysts  to  try 
the  speedier,  if  less  accurate  processes,  depending  on  the  use  of 
volumetric  methods.     The  chief  difficulty  with  these  methods  has 
been  in  securing  combinations  of  standard  composition  and  some 
sharp  method  of  distinguishing  the  end  reaction.     In  some  cases, 
as,  for  instance,  in  the  uranium  method,  it  has  been  found  neces- 
sary to  remove  a  portion  of  the  titrated  solution  and  prepare  it 
for  final  testing  by  subsidence  or  filtration.     As  is  well  known, 
this  method  of  determining  the  end  reaction  is  less  accurate  and 
more  time-consuming  than  those  processes  depending  on  a  change 

3  Journal  of  the  American  Chemical  Society,  1896,  18  :  23. 

4  Division  of  Chemistry,  Bulletin  51,  1898  :  47. 

6  Division  of  Chemistry,  Bulletin  49,  1897  :  60  ;  Bulletin  51,  1898  :  47. 


CLASSIFICATION    OF    METHODS  13! 

of  color  in  the  whole  mass.  Free  tribasic  phosphoric  acid  can  not 
be  conveniently  titrated  directly  with  a  standard  alkali,  because  of 
the  development  of  an  amphoteric  action  near  the  point  of  neu- 
trality. When,  for  instance,  an  alkali  is  added  to  the  acid,  a  com- 
bination is  formed  of  such  a  character  that  it  will  affect  an  indi- 
cator both  as  an  acid  and  alkali.  All  the  volumetric  processes 
now  in  general  use  may  be  divided  into  two  classes,  viz.,  (i)  the 
direct  titration  of  phosphoric  acid  and  the  determination  of  the 
end  reaction  by  any  appropriate  means,  and  (2)  the  previous 
separation  of  the  phosphoric  acid,  usually  by  means  of  a  citro- 
magnesium  or  molybdenum  mixture,  and  in  the  latter  case  the 
subsequent  titration  of  the  yellow  ammonium  phosphomolybdate 
either  directly  or  after  reduction  to  a  lower  form  of  oxidation. 
In  respect  of  age  and  extent  of  application,  by  far  the  most  im- 
portant volumetric  method  is  the  one  depending  on  titration  by  a 
uranium  salt  after  previous  separation  by  ammoniacal  magnesium 
citrate.  A  promising  method,  after  previous  separation  by 
molybdenum,  is  the  one  proposed  by  Thilo  and  developed  by  Pem- 
berton,  and  modified  by  Kilgore  and  other  members  of  the  Asso- 
ciation of  Official  Agricultural  Chemists,  and  it  has  now  come  into 
quite  general  use  in  this  country.  For  small  quantities  of  phos- 
phoric acid  or  of  phosphorus,  such  as  are  found  in  steels  and  irons, 
the  method  of  Emmerton  either  as  originally  proposed  or  as  modi- 
fied by  Dudley  and  Moves,  has  been  frequently  used.  Where  volu- 
metric methods  are  applied  to  products  separated  by  molybdic  solu- 
tion, the  essential  feature  of  the  analytical  work  is  to  secure  a  yel- 
low precipitate  of  constant  composition.  If  this  could  be  uniform- 
ly done  in  such  methods  they  would  rival  the  gravimetric  pro- 
cesses in  accuracy.  Hence  it  is  highly  important  in  these  methods 
that  the  yellow  precipitate  should  be  secured  as  far  as  possible 
under  constant  conditions  of  strength  of  solution,  duration  of 
time,  and  manner  of  precipitation.  In  these  cases,  and  in  such 
only,  can  the  quicker  volumetric  methods  be  depended  on  for 
accurate  results. 

The  direct  volumetric  titration  of  the  phosphoric  acid  by 
a  uranium  salt  or  otherwise  is  practised  only  when  the  acid  is 
combined  with  the  alkalies  and  when  iron  and  alumina  are 
absent  and  only  small  quantities  of  lime  present.  This  method 


132  AGRICULTURAL   ANALYSIS 

has  therefore,  but  little  practical  value  for  agricultural  purposes. 
In  all  volumetric  analyses  the  accuracy  of  the  burettes,  pipettes, 
and  other  graduated  vessels  should  be  proved  by  careful  calibra- 
tion. Many  of  the  disagreements  in  laboratories  where  the 
analytical  work  is  conducted  equally  well  can  be  due  to  no  other 
cause  than  the  inaccuracy  of  the  graduated  vessels  which  are  often 
found  in  commerce.  Burettes  should  not  only  be  calibrated  for 
the  whole  volume  but  for  at  least  every  five  cubic  centimeters  of 
the  graduation. 

URANIUM  METHOD  AS  PRACTISED  BY  THE  FRENCH 
CHEMISTS. 

118.  The  Uranium  Method. — Since  the  phosphoric  acid  of  prac- 
tical use  for  agricultural  purposes  is  nearly  always  combined  with 
lime,  alumina  and  iron,  its  volumetric  estimation  by  means  of  a 
standard  solution  of  a  uranium  salt  is  to  be  preceded  by  a  pre- 
liminary   separation   by    means    of   an    ammoniacal    magnesium 
citrate  solution.     The  phosphoric  acid  may  also  be  separated  by 
means  of  molybdic  solution  or  by  tin  or  bismuth.     The  principle 
of  the  method  was  almost  simultaneously  published  by  Sutton, 
Neubauer,  and  Pincus.6     In  practise,  however,  it  has  been  found 
that  when  the  uranium  method  is  to  be  used,  the  magnesium  cit- 
rate separation  is  the  most  convenient.  Since  this  is  the  method 
until  lately  practised  almost  universally  in  France,  it  will  be  given 
in  detail.     It  is  based  essentially  on  the  process  of  Joulie,7  as 
described  by  Munro.8 

119.  Preparation  of  Sample. —  (i)  Incineration. — Since  the  or- 
ganic matters  present  in  a  phosphatic  fertilizer  often  interfere 
with  the  employment  of  uranium  as  a  reagent,  it  is  necessary  to 
incinerate  the  sample  before  analysis.0 

(2)  Solution  of  the  Material. — All  phosphates,  with  the  excep- 
tion of  certain  aluminum  phosphates,  amblygonite  for  example, 
are  easily  dissolved  in  nitric  and  hydrochloric  acids  more  or  less 

6  Chemical  News,  1860,  1  197,  122;  Sutton,    Volumetric   Analysis,  gth 
Edition,  1904  :  298. 

Archive  fur  wissenschaftliche  Heilkunde,  1860,  4  :  228. 
Journal  fur  praktische  Chemie,  1859,  76  :  104. 

1  Bulletin  de  la  Socie'te'  des  Agriculteurs  de  France,   1876  :  53  ;    Ency- 
clope"die  chimique,  1888,  4  :  TO. 
"  Chemical  News,  1885.  52  :  85. 
•  Manuel  agenda  des  Fabricants  de  Sucre,  1889  :  307. 


PREPARATION   OF   SAMPLE  133 

dilute,  especially  on  ebullition.  The  best  solvent,  however,  for 
calcium  phosphates  in  the  uranium  method  is  incontestably  hy- 
drochloric acid  which  also  very  easily  dissolves  the  iron  and 
aluminum  phosphates  often  found  with  calcium  phosphates. 

(3)  Nitric  Acid. — In  many  laboratories  nitric  acid  is  preferred 
in  order  to  avoid,  in  part,  the  solution  of  ferric  oxid  which  inter- 
feres with  the  determination  of  phosphoric  acid  in  certain  pro- 
cesses.    Since  it  does  not  act  in  this  way  for  the  citro-magne- 
sium  uranium  method,  it  is  preferable  to  employ  hydrochloric  acid, 
especially  because  it  dissolves  the  iron  completely  and  thus  per- 
mits the  operator  to  judge  of  the  success  of  the  solvent  action  by 
the  completely  white  color  of  the  residue. 

(4)  Pyritic  Phosphates. — Certain   phosphates   contain   pyrites 
which  hydrochloric  acid  does  not  readily  dissolve,  and  there  is 
left,  consequently,  a  residue  more  or  less  colored.     In  this  case  it 
is  necessary  to  add  some  nitric  acid  and  to-  prolong  the  boiling 
until  the  pyrite  has  disappeared,   since  it  might  retain  a   small 
quantity  of  phosphoric  acid  in  the  state  of  iron  phosphate. 

(5)  Sulfuric  Acid. — Some  chemists  decompose  the  phosphates 
by  means  of  dilute  sulfuric  acid.     This   method,   which   is  cer- 
tainly able  to  give  good  results  for  certain  products  and  for  cer- 
tain   processes,    presents    numerous    inconveniences    tending    to 
render  its  use  objectionable  for  volumetric  purposes.     The  cal- 
cium sulfate   formed,    requires  prolonged  washings  which  lead 
to  chances  of  fatal  error. 

If  an  aluminum  phosphate  be  under  examination,  containing 
only  very  little  or  no  lime,  sulfuric  acid  is  to  be  preferred  to 
hydrochloric  and  nitric  acids,  since  it  attacks  amblygonite,  which, 
as  has  been  before  stated,  resists  the  action  of  the  other  two  acids. 
But  these  are  cases  which  are  met  with  very  rarely,  and  which 
can  always  be  treated  by  the  general  method  of  previously  fusing 
the  material  with  a  mixture  of  sodium  and  potassium  carbonate. 

In  the  great  majority  of  cases  the  decomposition  by  hydro- 
chloric acid  is  very  easily  accomplished  by  simply  boiling  in  a 
glass  vessel,  and  without  effecting  the  separation  of  the  silica. 
This  operation  is  only  necessary  after  the  substance  has  been 
fused  with  alkaline  carbonates,  or  in  case  of  substances  which 


134  AGRICULTURAL   ANALYSIS 

contain  decomposable  silicates  giving  gelatinous  silica  with  hydro- 
chloric acid. 

There  are  two  methods  [see  (6)  and  (7)]  of  securing  a  solu- 
tion of  the  sample  which  varies  from  one  to  five,  and  even  to  10 
grams,  according  to  the  apparent  quantity  of  phosphoric  acid  in 
the  material  to  be  analyzed. 

(6)  Solution  by  Filtration  and  Washing. — The  ordinary  method 
can  be   employed  consisting   in  decomposing  the   substance  by 
an  acid,  filtering,  washing  the  residue  upon  the  filter  and  com- 
bining all  the  wash-waters  to  make  a  determinate  volume.     After- 
wards an  aliquot  fraction  of  the  whole  is  used  for  the  precipita- 
tion.    This  method  is  long,  and  presents  some  chances  of  error 
when  the  insoluble  residue  is    voluminous    and    contains    silica 
which  obstructs  the  pores  of  the  paper  and  renders  the  filtration 
difficult. 

(7)  Volumetric  Solution. — It  is  advisable  to  substitute  volu- 
metric solution  for  solution  by  filtration  and  washing,  which  is 
accomplished  by  decomposing  the  substance  in  a  graduated  flask, 
the  volume  being  afterwards  made  up  to  the  mark  with  distilled 
water  after  cooling.     The  solution  is  filtered  without  washing, 
and  by  means  of  a  pipette  an  aliquot  part  of  the  original  volume 
is  removed  for  analysis.     Thus  all  retardations  in  the  process 
are  avoided,  and  likewise  the  chances  of  error  from  washing  on 
the  filter.     It  is  true  that  this  method  may  lead  to  a  certain  error 
due  to  the  volume  of  the  insoluble  matter  which  is  left  undecom- 
posed,  but  since  this  insoluble  matter  is  usually  small  in  quantity, 
and  since  it  is  always  possible  to  diminish  the  error  therefrom  by 
correspondingly  increasing  the  volume  of  the  solution,  this  cause 
of  error  is  much  less  to  be  feared  than  those  due  to  the  difficulties 
which  may  occur  in  the  other  method.     Let  us  suppose,  in  order  to 
illustrate  the  above,  that  we  are  dealing  with  a  phosphate  contain- 
ing 50  per  cent,  of  insoluble  sand  which  may  be  considered  as  an 
extreme  limit.     In  working  on  four  grams  of  the  material  in  a 
flask  of  100  cubic  centimeters  capacity,  there  will  be  an  insoluble 
residue  of  two  grams  occupying  a  volume  of  less  than  one  cubic 
centimeter,  the  density  of  the  sand  being  generally  above  two.  The 
100  cubic  centimeter  flask  will  then  contain  more  than  99  cubic 


PRECIPITATION    OF    THE   PHOSPHATE  135 

centimeters  of  the  real  solution  and  the  error  at  the  most  would 
be  less  than  o.oi.  This  error  could  be  reduced  to  one-half  by  dis- 
solving only  two  grams  of  the  material  in  place  of  four,  or  by  mak- 
ing the  volume  up  to  200  instead  of  100  cubic  centimeters. 

In  general  it  may  be  said  that  the  errors  which  do  not  exceed 
o.oi  of  the  total  matter  under  treatment,  are  negligible  for  all 
industrial  products.  The  method  of  volumetric  solution  does 
not  present  any  further  inconvenience.  It  deserves  to  be  and 
has  been  generally  adopted  by  reason  of  its  rapidity  in  all  the 
laboratories  where  many  analyses  are  to  be  made.  In  the  volu- 
metric method  great  care  should  be  taken  not  to  make  up  to  the 
volume  until  after  the  cooling  to  room  temperature,  which  may 
be  speedily  secured  by  immersing  the  flask  in  cold  water.  Care 
should  also  be  exercised  in  removing  the  sample  for  analysis  by 
means  of  the  pipette  immediately  after  filtration,  and  filtration 
should  take  place  as  soon  as  the  volume  is  made  up  to  the  stand- 
ard. By  operating  in  this  way  the  possible  variations  from 
changes  of  volume  due  to  changes  of  temperature  are  avoided. 

(8)  Examination  for  Arsenic  Acid. — When  the  sample  exam- 
ined contains  pyrites,  arsenic  is  often  present.  When  the  decom- 
position has  been  effected  by  means  of  nitric  acid,  arsenic  acid 
may  be  produced.  This  deports  itself  in  all  circumstances  like 
phosphoric  acid,  and  if  it  is  present  in  the  matter  under  exami- 
nation, it  will  be  found  united  with  the  phosphoric  acid  and  de- 
termined therewith  afterwards.  It  is  easy  to  avoid  this  cause  of 
error  by  passing  first  a  current  of  sulfurous  acid  through  the 
solution,  carrying  it  to  the  boiling  point  in  order  to  drive  out  the 
excess  of  sulfurous  acid,  and  afterwards  precipitating  the  arsenic 
by  a  current  of  hydrogen  sulfid.  After  filtration,  the  rest  of  the 
operation  can  be  carried  on  as  already  described. 

1 20.  Precipitation  of  the  Phosphate  in  Presence  of  Citrate. — 
By  means  of  an  accurate  pipette  a  quantity  of  the  solution  repre- 
senting from  0.125  to  0.250  gram  or  more  is  measured,  according 
to  the  presumed  richness  of  the  product  to  be  examined.  In  order 
that  the  following  operations  may  go  on  well,  it  is  advisable  that 
the  quantity  of  phosphoric  acid  contained  in  the  sample  should  be 
about  50  milligrams.  The  sample  being  measured  is  run  into  a 


136  AGRICULTURAL   ANALYSIS 

beaker,  and  there  are  added,  first,  10  cubic  centimeters  of  mag- 
nesium citrate  solution,  and  second,  a  large  excess  of  ammonia. 
If  the  quantity  of  the  magnesium  citrate  solution  be  sufficient,  the 
mixture  should  at  first  remain  perfectly  limpid  and  only  become 
turbid  at  the  end  of  some  moments  and  especially  after  the  mix- 
ture is  stirred. 

If  there  should  be  an  immediate  turbidity,  it  is  proof  that  the 
quantity  of  magnesium  citrate  solution  employed  has  been  in- 
sufficient to  hold  the  iron  and  aluminum  phosphates  in  solution 
until  the  new  compounds  are  formed,  and  it  is  necessary  to  be- 
gin again  by  doubling  its  amount.  Good  results  can  not  be  ob- 
tained by  adding  a  second  portion  of  the  magnesium  citrate  solu- 
tion to  the  original,  since  the  iron  and  aluminum  phosphates  which 
are  once  formed  are  redissolved  with  difficulty.  Many  chemists 
at  the  present  time  abstain  from  using  the  magnesium  citrate  solu- 
tion and  replace  it  by  a  solution  of  citric  acid  and  one  of  magne- 
sium sulfate,  which  they  pour  successively  into  the  sample  under 
examination.  This  is  a  cause  of  grave  errors  which  it  is  neces- 
sary to  point  out.  Joulie  has  indeed  recognized  the  fact  that 
the  precipitation  of  the  phosphoric  acid  is  not  completed  in  pres- 
ence of  ammonium  citrate  unless  it  is  employed  in  conjunction 
with  a  sufficient  excess  of  magnesia.  But  the  foreign  matters 
which  accompany  the  phosphoric  acid  require  different  quanti- 
ties of  ammonium  citrate  in  order  to  keep  them  in  solution,  and 
it  is  important  to  increase  the  magnesium  solution  at  the  time  of 
increasing  the  citric  acid  in  order  to  maintain  them  always  in 
the  same  proportion.  This  is  easily  accomplished  by  measuring 
the  two  solutions,  but  it  is  much  more  easily  done  by  uniting  them 
and  adding  them  together. 

121.  The  Magnesium  Citrate  Solution. — The  formula  originally 
proposed  by  Joulie,  modified  by  Millot,  and  adopted  by  the  French 
Association  of  Chemists,  is  as  follows :  Citric  acid,  400  grams ; 
pure  magnesium  carbonate,  40  grams ;  caustic  magnesia,  20  grams ; 
distilled  water,  half  a  liter.  After  solution,  add  enough  of  am- 
monia to  render  strongly  alkaline,  requiring  about  600  cubic 
centimeters.  Make  the  volume  up  with  distilled  water  to  one 
and  a  half  liters.  Tf  the  solution  be  turbid,  it  is  proof  that  the 


FILTRATION   AND   WASHING  137 

magnesia  or  the  carbonate  employed  contains  some  phosphoric 
acid,  which  is  to  be  separated  by  filtration,  and  the  solution  can 
then  be  preserved  indefinitely. 

This  solution  is  made  by  the  formula  given  by  Button  as  fol- 
lows: Add  27  grams  of  pure  magnesium  carbonate  by  degrees 
to  a  solution  of  270  grams  of  citric  acid  in  350  cubic  centimeters 
of  warm  water.  When  all  effervescence  has  ceased  and  the  liquid 
is  cooled  to  room  temperature,  add  400  cubic  centimeters  of  am- 
monia of  about  0.96  specific  gravity,  containing  approximately 
10  per  cent,  of  NH3.  The  volume  is  made  up  to  one  liter  and  kept 
in  a  well  stoppered  bottle.10 

122.  Time  of  Subsidence. — When  the  phosphoric  acid  is  precipi- 
tated by  the  mixture  above  mentioned,  it  is  necessary  to  allow  it 
to  subside  for  a  certain  time  under  a  bell  jar  in  order  to  avoid  the 
evaporation  of  the  ammonia.     In  order  to  give  plenty  of  time 
for  this  subsidence,  it  is  well  to  make  the  precipitations  in  the 
afternoon  and  the  filtrations  the  following  morning.     There  are 
thus  secured  from  12  to  15  hours  of  repose,  which  is  time  amply 
sufficient  for  all  cases. 

123.  Filtration  and  Washing. — Filtration  is  performed  easily 
and  rapidly  upon  a  small  filter  without  folds  placed  in  a  funnel 
with  a  long  stem  of  about  two  millimeters  internal   diameter. 
Placed  in  a  series  of  six  or  eight,  they  allow  the  filtration  to  take 
place  in  regular  order  without  loss  of  time,  the  first  filter  being  al- 
ways empty  by  the  time  the  last  one  is  filled.     The  supernatant 
liquid  from  the  precipitate  should  first  be  decanted  on  the  filter, 
avoiding  the  throwing  of  the  filtrate  on  the  filter,  which  would 
greatly  retard  the  process,  especially  if  it  should  contain  a  little 
silica,  as  often  happens. 

When  the  clear  liquid  is  thus  decanted  as  completely  as  possi- 
ble, the  rest  of  the  precipitate  is  treated  with  water  to  which  one- 
tenth  of  its  volume  of  ammonia  has  been  added,  and  the  washing 
is  continued  by  decantation  as  at  first,  and  afterwards  by  wash- 
ing upon  the  filter  until  the  filtered  solution  gives  no  precipitate 
with  sodium  phosphate.  Four  washings  are  generally  sufficient 
to  attain  this  result. 

10  Sutton,  Volumetric  Analysis,  gth  Edition,  1904:    299. 


138  AGRICULTURAL   ANALYSIS 

If  the  operations  which  precede  have  been  well  conducted,  the 
total  phosphoric  acid  contained  in  the  material  under  examina- 
tion is  found  upon  the  filter  paper,  except  the  small  portion  which 
remains  adhering  to  the  beaker  in  which  the  precipitation  has 
been  made.  The  determination  of  the  phosphoric  acid  comprises 
the  following  operations :  First,  solution  of  the  ammonium  mag- 
nesium phosphate,  and  second,  titration  by  means  of  a  standard 
solution  of  uranium. 

124.  Solution  of  the  Ammonium  Magnesium  Phosphate. — The 
phosphate  which  has  been  collected  upon  the  filter  is  dissolved  by 
a  10  per  cent,  solution  of  pure  nitric  acid.     This  solution  is  caused 
to  pass  into  the  beaker  in  which  the  precipitation  was  made  in 
order  to  dissolve  the  particles  of  phosphate  which  remain  adherent 
to  its  sides ;  and  this  solution  is  then  thrown  upon  the  filter.    The 
filtrate  is  then  received  in  a  flask  of  about  150  cubic  centimeters 
capacity,  marked  at  75  cubic  centimeters.     After  two  or  three 
washings  with  the  acidulated  water,  the  filter  itself  is  detached 
from  the  funnel  and  introduced  into  the  vessel  which  contains 
the  solution. 

The  whole  of  the  filtrate  being  collected  in  the  flask,  it  is  sat- 
urated by  one-tenth  ammoniacal  water  until  a  slight  turbidity  is 
produced.  One  or  two  drops  of  dilute  nitric  acid  are  now  added 
until  the  liquor  becomes  limpid,  and  the  flask  is  placed  upon  a 
sand-bath  in  order  to  carry  the  liquid  to  the  boiling-point.  After 
ebullition  there  is  added  five  cubic  centimeters  of  acid  sodium 
acetate  so  as  to  cause  the  free  nitric  acid  to  disappear,  and 
immediately  the  titration,  by  means  of  a  standard  solution  of 
uranium,  is  undertaken. 

125.  Acid  Sodium  Acetate. — The  acid  sodium  acetate  is  prepared 
as  follows :    Crystallized  sodium  acetate,  100  grams  ;  glacial  acetic 
acid,  50  cubic  centimeters ;  distilled  water,  enough  to  make  one 
liter. 

126.  Standard  Solution  of  Uranium  Nitrate. — A  solution  of  ura- 
nium is  to  be  prepared  as  follows :     Pure  uranium  nitrate,  40 
grams ;   distilled  water,  about  800  cubic  centimeters.     Dissolve 
the  uranium  nitrate  in  the  distilled  water  and  add  a  few  drops  of 
ammonia  until  a  slight  turbidity  is  produced,  and  then  a  sufficient 


TYPICAL   SOLUTION   OF   PHOSPHORIC   ACID  139 

amount  of  acetic  acid  to  cause  this  turbidity  to  disappear.  The 
volume  is  then  completed  to  one  liter  with  distilled  water. 

The  uranium  nitrate  often  contains  some  uranium  phosphate 
and  some  ferric  nitrate.  It  is  important  that  it  be  freed  from 
these  foreign  substances.  This  is  secured  by  dissolving  it  in  dis- 
tilled water  and  precipitating  it  by  sodium  carbonate,  which  re- 
dissolves  the  uranium  oxid  and  precipitates  the  iron  phosphate 
and  oxid. 

The  filtered  liquor  is  saturated  with  nitric  acid  and  the  uranium 
oxid  reprecipitated  by  ammonia.  It  is  washed  with  distilled  water 
by  decantation  and  redissolved  in  nitric  acid,  as  exactly  as  possi- 
ble, evaporated,  and  crystallized. 

The  crystals  are  taken  up  with  ether,  which  often  leaves  behind 
a  little  insoluble  matter.  The  solution  is  filtered,  and  the  ether 
evaporated.  The  salt  which  remains  is  perfectly  pure. 

It  frequently  happens  when  the  uranium  nitrate  has  not  been 
properly  purified  that  the  solution,  prepared  as  has  been  indicated 
above,  deposits  a  light  precipitate  of  phosphate  w^hich  alters  its 
strength  and  affords  a  cause  of  error. 

Only  those  solutions  should  be  employed  which  have  been  pre- 
pared some  days  in  advance  and  which  have  remained  perfectly 
limpid.  The  solution  of  uranium  thus  obtained  contains  uranium 
nitrate,  a  little  ammonium  nitrate,  a  very  small  quantity  of  ura- 
nium acetate,  some  ammonium  acetate,  and  a  little  free  acetic 
acid.  Its  sensibility  is  the  more  pronounced  as  the  acetates  pres- 
ent in  it  are  less  in  quantity.  It  is  important,  therefore,  never  to 
prepare  the  solution  with  uranium  acetate. 

127.  Typical  Solution  of  Phosphoric  Acid. — In  order  to  titrate  a 
solution  of  uranium,  it  is  necessary  to  have  a  standard  solution 
of  phosphoric  acid ;  that  is  to  say,  a  solution  containing  a  precise 
and  known  quantity  of  that  acid  in  a  given  volume.  This  solu- 
tion is  prepared  by  means  of  acid  ammonium  phosphate,  a  salt 
which  is  easily  obtained  pure  and  dry.  Sometimes  it  may  con- 
tain a  small  quantity  of  neutral  phosphate,  which  modifies  the 
relative  proportions  of  phosphoric  acid  and  ammonia,  and  it  is 
indispensable  to  have  its  strength  verified.  The  titer  of  the  typical 
solution  should  be  such  that  it  requires  for  the  precipitation  of 


I4O  AGRICULTURAL    ANALYSIS 

the  phosphoric  acid  which  it  contains,  a  volume  of  the  solution 
of  uranium  almost  exactly  equal  to  its  own,  in  order  that  the 
expansions  or  contractions  which  the  two  liquors  undergo,  by  rea- 
son of  changes  in  the  temperature  of  the  laboratory,  should  be 
without  influence  upon  the  results. 

The  solution  of  uranium,  prepared  as  has  been  indicated  above, 
precipitates  almost  exactly  five  milligrams  of  phosphoric  acid  per 
cubic  centimeter;  the  typical  solution  of  phosphoric  acid  is  pre- 
pared with  eight  and  one-tenth  grams  of  acid  ammonium  phos- 
phate pure  and  dry,  which  is  dissolved  in  a  sufficient  quantity  of 
distilled  water  to  make  one  liter. 

Since  the  acid  ammonium  phosphate  contains  61.74  per  cent, 
of  anhydrous  phosphoric  acid,  the  quantity  above  gives  exactly 
five  grams  of  that  acid  in  a  liter,  or  five  milligrams  in  a  cubic 
centimeter. 

Instead  of  this  solution  the  following  is  also  recommended : 
Dissolve  3.087  grams  of  pure  ammonium  phosphate  in  water  and 
make  the  volume  up  to  one  liter.  Each  20  cubic  centimeters  of 
this  solution  corresponds  to  0.04  gram  of  phosphoric  anhydrid. 

128.  Salt  for  Setting  the  Uranium  Solution. — In  determining  the 
strength  of  the   uranium   solution  the  crystallized  sodium  salt, 
Na,HPO4.H2O,  has  been  used.     This  salt  easily  loses  water  and 
for  this  reason  its  weight  is  not  constant.     Miiller  proposes  to 
use  in  its  place,  the  acid  sodium-ammonium  salt,  NaHNH4PO4. 
4H2O.     Even  better  results  are  secured  by  using  the  crystallized 
dicalcium  salt,   CaHPO4.2H2O,   which  in  the  free  air  or  even 
over  phosphoric  anhydrid  does  not  vary  at  ordinary  tempera- 
tures.11 

In  the  preparation  of  this  salt  a  solution  of  disodium  phos- 
phate, Na2HPO4,  is  added  little  by  little  to  a  dilute  solution  of  cal- 
cium chlorid  until  the  lime  is  almost  completely  precipitated. 
The  gelatinous  precipitate  at  first  formed  soon  becomes  crystalline, 
and  it  is  easy  to  wash  it  thoroughly.  The  washed  salt  is  placed 
on  plates  and  dried  at  70°.  Theoretically,  the  salt  thus  obtained 
contains  41.27  per  cent,  of  P2O5. 

129.  Verification  of  the  Strength  of  the  Standard  Solution  of 
Phosphoric  Acid. — The  strength  of  the  standard  solution  of  phos- 

11  Bulletin  de  la  Soci£t£  chimique  de  Paris,  1901,  [3],  25  :  1000. 


TITRATION   OF   SOLUTION   OF  URANIUM  141 

phoric  acid  is  verified  by  evaporating  a  known  volume,  50  cubic 
centimeters,  for  example,  with  a  solution  of  ferric  hydroxid  con- 
taining a  known  quantity  of  ferric  oxid.  The  mass  having  been 
evaporated  to  dryness  and  ignited  in  a  platinum  crucible,  gives 
an  increase  in  the  weight  of  the  iron  oxid  exactly  equal  to  the 
amount  of  anhydrous  phosphoric  acid  contained  therein,  both  the 
nitric  acid  and  ammonia  being  driven  off  by  the  heat. 

To  prepare  the  solution  of  ferric  hydroxid,  dissolve  20 
grams  of  iron  filings  in  hydrochloric  acid.  The  solution  is  filtered 
to  separate  the  carbon,  and  it  is  converted  into  ferric  nitrate  by 
nitric  acid ;  then  the  solution  is  diluted  with  distilled  water  and  the 
ferric  oxid  precipitated  by  a  slight  excess  of  ammonia.  The  pre- 
cipitate, washed  by  decantation  with  distilled  water  until  the 
wash-water  no  longer  gives  a  precipitate  with  silver  nitrate,  is 
redissolved  in  nitric  acid  and  the  solution  is  concentrated  or  di- 
luted, as  the  case  may  be,  to  bring  the  volume  to  one  liter. 

In  order  to  determine  the  quantity  of  ferric  oxid  which  it  con- 
tains, 50  cubic  centimeters  are  evaporated  to  dryness,  ignited, 
and  weighed. 

A  second  operation  like  the  above  is  carried  on  by  adding  50 
cubic  centimeters  of  the  standard  solution  of  phosphoric  acid, 
and  the  strength  of  the  solution  thus  obtained  is  marked  upon 
the  flask. 

If  the  operation  has  been  properly  carried  on,  three  or  four  du- 
plicates will  give  exactly  the  same  figures.  If  there  are  sensible 
differences,  the  whole  operation  should  be  done  over  from  the 
first. 

130.  Titration  of  the  Solution  of  Uranium. — In  a  150  cubic  cen- 
timeter flask  marked  at  75  cubic  centimeters,  are  poured  10 
cubic  centimeters  of  the  standard  solution  of  phosphoric  acid 
measured  with  an  exact  pipette ;  five  cubic  centimeters  of  the  acid 
sodium  acetate  are  added,  and  distilled  water  enough  to  make 
about  30  cubic  centimeters,  and  the  whole  carried  to  the  boil- 
ing-point. The  titration  is  then  carried  on  by  allowing  the  solu- 
tion of  uranium  to  fall  into  the  flask  from  a  graduated  burette, 
thoroughly  shaking  after  each  addition  of  the  uranium,  and  try- 
ing a  drop  of  the  liquor  with  an  equal  quantity  of  a  10  per  cent. 


142  AGRICULTURAL  ANALYSIS 

solution  of  potassium  ferrocyanid  upon  a  greased  white  plate. 
Since  the  quantity  of  the  uranium  solution  present  will  be  very 
nearly  10  cubic  centimeters  at  first,  nine  cubic  centimeters  can 
be  run  in  without  testing.  Afterwards,  the  operation  is  continued 
by  adding  two  or  three  drops  at  a  time  until  the  test  upon  the 
white  plate  with  the  potassium  ferrocyanid  shows  the  end  of  the 
reaction.  When  there  is  observed  in  the  final  test  a  slight  change 
of  tint,  the  flask  is  filled  up  to  the  mark  with  boiling  distilled 
water  and  the  process  tried  anew.  If  in  the  first  part  of  the  opera- 
tion the  point  of  saturation  has  not  been  passed,  usually  the  ad- 
dition of  a  drop  or  two  of  the  uranium  solution  is  required  in  order 
to  produce  the  characteristic  reddish  coloration,  and  this  increase 
is  rendered  necessary  by  the  increase  in  the  volume  of  the  liquid. 
Proceeding  in  this  manner  two  or  three  times  assures  the  attain- 
ment of  extreme  precision,  inasmuch  as  the  analyst  knows  just 
when  to  look  for  the  point  of  saturation. 

Correction. — The  result  of  the  preceding  operation  is  not  abso- 
lutely exact.  It  is  evident,  indeed,  that  in  addition  to  the  quantity 
of  uranium  required  for  the  exact  precipitation  of  the  phosphoric 
acid,  it  has  been  necessary  to  add  an  excess  sufficient  to  produce 
the  reaction  upon  the  potassium  ferrocyanid. 

This  excess  is  rendered  constant  by  the  precaution  of  operating 
always  upon  the  same  volume,  namely,  75  cubic  centimeters.  It 
can  be  determined  then,  once  for  all,  by  making  a  blank  deter- 
mination under  the  same  conditions  but  without  using  the  phos- 
phoric acid. 

The  result  of  this  determination  is  that  it  renders  possible  the 
correction,  which  it  is  necessary  to  make,  by  subtracting  the  quan- 
tity used  in  the  blank  titration  from  the  preceding  result  in 
order  to  obtain  the  exact  strength  of  the  uranium  solution. 

The  operation  is  carried  on  as  follows:  In  a  flat-bottomed 
flask  of  about  150  cubic  centimeters  capacity  and  marked  at 
75  cubic  centimeters,  by  means  of  a  pipette,  are  placed 
five  cubic  centimeters  of  the  solution  of  sodium  acetate ;  some 
hot  distilled  water  is  added  until  the  flask  is  filled  to  the  mark, 
and  it  is  then  placed  upon  a  sand-bath  and  heated  to  the  boiling- 
point.  It  is  taken  from  the  fire,  the  volume  made  up  to  75 


TITRATION   OF  THE   SOLUTION   OF   URANIUM  143 

cubic  centimeters  with  a  little  hot  distilled  water,  and  one 
or  two  drops  of  the  solution  of  uranium  are  allowed  to  flow  into 
the  flask  from  a  graduated  burette  previously  filled  exactly  to 
zero.  After  each  drop  of  the  solution  of  uranium,  the  flask  is 
shaken  and  the  liquid  tried  upon  a  drop  of  potassium  ferrocyanid, 
as  has  been  previously  indicated.  For  a  skilled  eye,  four  to  six 
drops  are  generally  necessary  to  obtain  the  characteristic  colora- 
tion, that  is,  from  two-tenths  to  three-tenths  of  a  cubic  centi- 
meter. Beginners  often  use  from  five-tenths  to  six-tenths,  and 
sometimes  even  more. 

The  sole  important  point  is  to  arrest  the  operation  as  soon  as 
the  reddish  tint  is  surely  seen,  for  afterwards  the  intensity  of  the 
coloration  does  not  increase  proportionally  to  the  quantity  of 
liquor  employed. 

It  is  well  to  note  that  at  the  end  of  some  time  the  coloration 
becomes  more  intense  than  at  the  moment  when  the  solutions 
are  mixed,  so  that  care  must  be  taken  not  to  pass  the  saturation- 
point.  This  slowness  of  the  reaction  is  the  more  marked  as  there 
is  more  sodium  or  ammonium  acetate  in  the  standard  solutions. 
This  is  the  reason  that  it  is  important  to  introduce  always  the 
same  quantity,  namely,  five  cubic  centimeters.  This  is  also  the 
reason  why  the  uranium  acetate  should  not  be  employed  in  pre- 
paring the  standard  solution  of  uranium  which  ought  to  contain 
the  least  possible  amount  of  acetate  in  order  that  the  necessary 
quantity  which  is  carried  into  each  test  should  be  as  small  as 
possible  and  remain  without  appreciable  influence.  If  it  were 
otherwise,  the  sensibility  of  the  reaction  would  be  diminished 
ir  proportion  as  a  larger  quantity  of  uranium  solution  was  em- 
ployed, giving  rise  to  errors  which  would  be  as  much  more  im- 
portant as  the  quantities  of  phosphoric  acid  to  be  determined  were 
greater.  The  correction  for  the  uranium  solution  having  been 
determined,  it  is  written  upon  the  label  of  the  bottle  containing  it. 

Causes  of  Error. — In  the  work  which  has  just  been  described, 
some  causes  of  error  may  occur  to  which  the  attention  of  analysts 
should  be  called. 

The  first  is  the  error  which  may  arise  from  the  consumption 
of  the  small  quantity  of  uranium  phosphate  which  is  taken  with 


144  AGRICULTURAL   ANALYSIS 

a  stirring  rod  when  the  liquid  is  tested  with  potassium  ferro- 
cyanid.  It  is  very  easy  to  be  assured  that  the  end  of  the  reaction 
has  really  been  reached.  For  this  purpose  it  is  only  necessary  to 
note  the  quantity  of  the  solution  already  employed  and  to  add  to 
it  afterwards  four  drops ;  shake,  and  make  a  new  test  with  a  drop 
of  the  potassium  ferrocyanid  placed  near  the  spot  which  the  last 
one  occupied.  If  a  decidedly  reddish  tint  does  not  appear  at  the 
moment  of  removing  the  glass  rod,  it  is  to  be  concluded  that  the 
first  appearance  was  an  illusion,  and  the  addition  of  uranium  is 
to  be  continued.  If,  on  the  contrary,  the  coloration  appear  of  a 
decided  tint,  the  preceding  number  may  be  taken  for  exact.  It 
is  then  always  beneficial  to  close  the  titration  by  this  test  of  four 
supplementary  drops  which  will  exaggerate  the  coloration  and 
confirm  the  figure  found. 

The  second  cause  of  error,  and  one,  moreover,  which  is  the  most 
frequently  met  with,  consists  in  passing  the  end  of  the  reaction 
by  adding  the  uranium  too  rapidly.  In  place  of  giving  then  a 
coloration  scarcely  perceptible,  the  test  with  the  drop  of  potas- 
sium ferrocyanid  gives  a  very  marked  coloration.  In  this  case 
the  analysis  can  still  be  saved.  For  this  purpose  the  analyst  has 
at  his  disposal,  a  tenth-normal  solution  prepared  with  100  cubic 
centimeters  of  the  standard  solution  of  phosphoric  acid  diluted  to 
one  liter  with  distilled  water.  Ten  cubic  centimeters  of  this  tenth- 
normal  solution  are  added,  and  the  titration  continued.  At  the 
end,  the  amount  of  additional  phosphoric  acid  used  is  subtracted 
from  the  total. 

A  third  cause  of  error  is  found  in  the  foam  which  is  often  found 
in  the  liquid,  due  to  shaking.  This  foam  may  retain  a  por- 
tion of  the  last  drops  of  the  solution  of  uranium  which  fall  upon 
its  surface  and  prevent  its  mixture  with  the  rest  of  the  liquid. 
If  the  glass  stirring  rod  in  being  removed  from  the  vessel,  pass 
through  this  froth  charged  with  uranium,  the  characteristic  col- 
oration is  obtained  before  real  saturation  is  reached.  Conse- 
quently it  is  necessary  to  avoid,  as  much  as  possible,  the  forma- 
tion of  the  foam,  and  especially  to  take  care  never  to  take  the 
drop  for  test  after  agitation  except  in  the  middle  of  the  liquid, 
where  the  foam  does  not  exist. 


TITRATION   OF   SAMPLE  145 

Suppose  the  titration  has  been  made  upon  10  cubic  centime- 
ters of  the  normal  solution  of  phosphoric  acid  in  the  conditions 
which  we  have  just  indicated,  and  the  figure  for  the  uranium 
obtained  is  10.2  cubic  centimeters;  if  now  the  correction,  which 
may  be  supposed  to  amount  to  two-tenths  cubic  centimeter,  be 
subtracted  there  will  remain  10  cubic  centimeters  of  the  uranium 
solution  which  wrould  have  precipitated  exactly  50  milligrams 
of  phosphoric  acid. 

The  quantity  of  phosphoric  acid  which  precipitates  one  cubic 
centimeter  of  the  solution  will  be  consequently  expressed  by  the 
proportion  50-^-10^:5  milligrams,  which  is  exactly  the  strength  re- 
quired. In  the  example  which  has  just  been  given,  the  inscrip- 
tion upon  the  flask  holding  the  standard  solution  would  be  as 
follows:  Solution  of  uranium,  one  cubic  centimeter  equals  five 
milligrams  of  phosphorus  pentoxid;  correction,  two-tenths  cubic 
centimeter. 

131.  Titration  of  the  Sample. — The  strength  of  the  solution  of 
uranium  having  been  exactly  determined,  by  means  of  this  solution 
the  strength  of  the  sample  in  which  the  phosphoric  acid  has  been 
previously  prepared  as  ammonium  magnesium  phosphate  is  as- 
certained. In  this  case  the  quantity  of  phosphoric  acid  being  un- 
known, it  is  necessary  to  proceed  slowly  and  to  duplicate  the  tests 
in  order  not  to  pass  beyond  the  point  of  saturation.  From  this 
there  necessarily  results  a  certain  error  in  consequence  of  the 
removal  of  quite  a  number  of  drops  of  the  solution  of  the  sample 
before  the  saturation  is  complete.  It  is,  therefore,  necessary  to 
make  a  second  determination  in  which  there  is  at  once  added 
almost  the  quantity  of  the  solution  of  uranium  determined  by 
the  first  analysis.  Afterwards  the  analysis  is  finished  by  addi- 
tions of  very  small  quantities  of  uranium  until  saturation  is 
reached.  Suppose,  for  instance,  that  the  sample  was  that  of  a 
mineral  phosphate,  five  grams  of  which  were  dissolved  in  100 
cubic  centimeters,  and  of  which  10  cubic  centimeters  of  the  solu- 
tion prepared  as  above,  required  15.3  cubic  centimeters  of  the 
standard  solution  of  uranium.  We  then  would  have  the  following 
data : 


146  AGRICULTURAL   ANALYSIS 

Mineral  phosphate,  five  grams  of  the  material  dissolved  in 
20  cubic  centimeters  of  hydrochloric  acid. 

Water,  sufficient  quantity  to  make  100  cubic  centimeters. 

Quantity  used,  10  cubic  centimeters=o.5o  gram  of  the  sample 
under  examination. 

Solution  of  uranium  required  15.3  cubic  centimeters. 

Correction  0.2  cubic  centimeters. 


Actual  quantity  of  uranium  solution  15.1  cubic  centimeters. 

Strength  of  the  solution  of  uranium,  one  cubic  centimeter=five 
milligrams  P2O5. 

Then  P2O5  in  0.50  gram  of  the  material  =  5  X  15.1  =  75-5 
milligrams. 

Then  the  per  cent,  of  P,O5  =  75'5  *  I(*    =15.10. 

The  sample  under  examination  ought  always  to  be  prepared  in 
duplicate,  either  by  making  a  single  precipitation  and  re-solution 
of  the  ammonium  magnesium  phosphate  which  is  made  up  to  a 
certain  volume  and  an  aliquot  portion  of  which  is  taken  for  the 
analysis,  or  by  making  two  precipitations  under  the  conditions 
previously  described.  When  the  content  of  phosphoric  acid  in 
the  material  under  examination  is  very  nearly  known,  the  double 
operation  may  be  avoided,  especially  if  it  be  required  to  have 
rapid  and  only  approximate  analyses,  such  as  those  which  are 
made  for  general  control  and  for  the  conduct  of  manufacturing 
operations.  But  when  analyses  are  to  be  used  to  serve  as  the 
basis  of  a  law  action  or  for  the  control  of  a  market,  they  should 
always  be  made  in  duplicate,  and  the  results  ought  not  to  be  ac- 
cepted when  the  numbers  obtained  are  widely  different,  since  the 
agreement  of  the  two  numbers  will  tend  to  show  that  the  work 
has  been  well  executed. 

This  method  of  analysis,  much  longer  to  describe  than  to  exe- 
cute, gives  results  perfectly  exact  and  always  concordant  when 
it  is  well  carried  out,  provided  that  the  standard  solutions  upon 
which  it  rests  for  its  accuracy  are  correctly  prepared  and  fre- 
quently verified  in  the  manner  indicated. 

The  strength  of  the  solution  of  uranium  ought  to  be  verified 


147 

every  three  or  four  days.  The  strength  of  the  standard  solution 
of  phosphoric  acid  should  be  verified  each  time  that  the  tempera- 
ture of  the  laboratory  undergoes  any  important  change.  A  solu- 
tion prepared,  for  example,  in  winter  when  the  temperature  of 
the  laboratory  is  from  15°  to  18°,  would  no  longer  be  exact  in 
summer  when  the  temperature  reaches  28°  or  30°. 

132.  Volumetric  Determination  of  Phosphoric  Acid  in  Super- 
phosphates.— Superphosphates  are  the  products  of  the  decomposi- 
tion of  phosphates  by  sulfuric  or  hydrochloric  acid.     They  con- 
tain phosphoric  acid  combined  with  water,  with  lime,  with  magne- 
sia, and  with  iron  and  alumina  in  various  proportions. 

These  combinations  may  be  classed  in  three  categories :  First, 
those  compounds  of  phosphoric  acid  soluble  in  water ;  second, 
those  insoluble  in  water,  but  very  soluble  in  ammoniacal  salts  of 
the  organic  acids  such  as  the  citrate  and  oxalate ;  and  third,  phos- 
phates not  soluble  in  any  of  the  above  named  reagents. 

In  the  products  soluble  in  water  are  met  free  phosphoric  acid, 
monocalcium  phosphate,  acid  magnesium  phosphate,  and  the  iron 
and  aluminum  phosphates  dissolved  in  the  excess  of  phosphoric 
acid.  In  the  products  insoluble  in  water  but  soluble  in  the  am- 
monium citrate  are  found  dicalcium  phosphate  and  iron  and 
aluminum  phosphates,  which  together  constitute  the  phosphates 
called  reverted. 

These  compounds  reduced  to  a  very  fine  state  of  division  in  the 
process  of  manufacture  are  considered  to  contain  phosphoric  acid 
of  the  same  economic  value  as  that  soluble  in  water. 

133.  Determination  of  the  Total  Phosphoric  Acid  in  Superphos- 
phates and  Fertilizers. — The  process  is  carried  on  exactly  as  for 
an  ordinary  phosphate,  and  with  all  the  care  indicated  in  connec- 
tion with  the  sampling,  the  incineration,  the  solution  by  mean>  of 
hydrochloric  acid,  and  the  separation  of  the  phosphoric  acid  in  the 
state  of  ammonium  magnesium  phosphate,  and  finally  in  the  titra- 
tion  with  uranium  nitrate. 

134.  Determination  of  Soluble  and  Reverted  Phosphoric  Acid. 
—To  make  this  determination  a  method  applicable  to  all  cases 

consists  in  extracting,  at  first,  the  constituents  soluble  in  distilled 
water,  and  following  this  operation  by  digesting  the  residue  in 


148  AGRICULTURAL   ANALYSIS 

ammonium  citrate.  The  products  soluble  in  water  can  be  deter- 
mined either  separately  or  at  the  same  time  as  the  products  solu- 
ble in  the  ammonium  citrate,  without  the  necessity  of  mod- 
ifying very  greatly  the  method  of  operation 

The  determination  of  the  total  soluble  or  available  phosphoric 
acid  comprises,  first,  the  solution  of  the  soluble  constituents  in  dis- 
tilled water;  second,  the  solution  of  the  reverted  phosphates  in 
ammonium  citrate ;  third,  the  determination  of  the  phosphoric  acid 
dissolved  in  the  two  preceding  operations  or  the  determination  of 
the  part  soluble  in  ammonium  nitrate  by  difference. 

135.  Preparation  of  the  Sample  for  Analysis. — The  sample  sent 
to  the  chemical  expert  is  prepared  as  has  been  indicated ;  that  is 
to  say,  it  is  poured  on  a  sieve  of  which  the  meshes  have  a  diameter 
of  one  millimeter,  and  sifted  upon  a  sheet  of  white  paper.     The 
parts  which  do  not  pass  the  sieve  are  broken  up  either  by  the 
hand  or  in  a  mortar  and  added,  through  the  sieve,  to  the  first 
portions.     The  product  is  well  mixed  and,  in  this  state,  the  mass 
presents  all  the  homogeneity  desirable  for  analysis. 

Some  fertilizers  are  received  in  a  pasty  state,  which  does  not 
permit  of  their  being  sifted.  It  is  necessary  in  such  a  case  to 
mix  them  with  their  own  weight  either  of  precipitated  calcium 
sulfate  dried  at  160°  or  with  fine  sand  washed  with  hydrochloric 
acid  and  dried,  which  divides  the  particles  perfectly  and  permits 
of  their  being  passed  through  the  meshes  of  the  sieve. 

136.  Extraction  of  the  Products  Soluble  in  Distilled  Water. — 
The  substance  having  been  prepared  as  has  just  been  indicated, 
one  and  a  half  grams  are  placed  in  a  glass  mortar.  Twenty  cubic 
centimeters  of  distilled  water  are  added,  and  the  substance  gently 
suspended  therein.     After  standing  for  one  minute,  the  super- 
natant part  is  decanted  into  a  small  funnel  provided  with  a  filter- 
paper  and  placed  in  a  flask  marked  at  150  cubic  centimeters.  This 
operation  is  repeated  five  times  and  is  terminated  by  an  intimate 
breaking  up  of  the  matter  with  distilled  water.    When  the  volume 
of  100  cubic  centimeters  of  the  filtrate  has  been  obtained,  the 
residue  in  the  mortar  is  placed  on  the  filter  and  the  washing  is 
continued  until  the  total  volume  reaches   150  cubic  centimeters. 
The  filtrate  is  shaken  in  order  to  render  the  liquor  homogeneous, 


SOLUTION   OF   REVERTED   PHOSPHATES  149 

and  is  transferred  to  a  precipitating  glass  of  about  300  cubic 
centimeters  capacity. 

137.  Solution  of  the  Reverted  Phosphates  by  Ammonium  Citrate. 
— The  filter  from  the  above  process  is  detached  from  the  funnel 
and  is  introduced  into  a  flask  marked  at  150  cubic  centimeters 
together  with  60  cubic  centimeters  of  alkaline  ammonium  citrate 
prepared  in  the  following  manner : 
Pure  citric  acid,  400  grams. 
Ammonia  of  22°,  500  cubic  centimeters. 

The  ammonia  is  poured  upon  the  crystals  of  citric  acid  in  a 
large  dish.  The  mass  becomes  heated,  and  the  solution  takes  place 
rapidly.  When  it  is  complete  and  the  solution  is  cold,  it  is  poured 
into  a  flask  of  one  liter  capacity,  and  the  flask  is  filled  up  to  the 
mark  with  strong  ammonia.  It  is  preserved  for  use  in  a  well 
stoppered  bottle.  The  solution  must  be  strongly  alkaline. 

The  flask  in  which  the  filter  paper  is  introduced,  together  with 
the  ammonium  citrate,  is  stoppered  and  shaken  violently  in  order 
to  disintegrate  the  filter  paper  and  get  the  reverted  phosphates 
in  suspension.  There  are  added  then  about  60  cubic  centi- 
meters of  distilled  water,  and  the  flask  is  shaken  and  left  for 
12  hours  at  least,  or  at  most  for  24  hours.  The  volume  is 
made  up  to  150  cubic  centimeters  with  distilled  water,  and  after 
mixture  the  solution  is  filtered. 

There  are  thus  obtained  two  solutions,  one  with  water  and  one 
with  the  alkaline  ammonium  citrate,  which  can  be  precipitated 
together  or  separately,  according  to  circumstances.  The  usual 
process  is  to  combine  equal  volumes  of  25,  50,  or  100  cubic 
centimeters,  representing  one-quarter,  one-half  or  one  gram  of 
the  material  according  to  its  presumed  richness,  in  a  precipitat- 
ing flask  to  which  are  added  from  10  to  20  cubic  centimeters  of 
the  solution  of  magnesia  made  up  as  follows : 

Magnesium  carbonate,  50  grams. 
Ammonium  chlorid,  100  grams. 
Water,  500  cubic  centimeters. 

Hydrochloric  acid,         120  cubic  centimeters. 

After  complete  solution  of  the  solid  matters  in  the  above,  add 


150  AGRICULTURAL   ANALYSIS 

100  cubic  centimeters  of  ammonia  of  22°  strength,  and  distilled 
water  enough  to  make  one  liter. 

The  solutions  are  thoroughly  mixed  in  a  precipitating  glass,  an 
excess  of  ammonia  added,  and  allowed  to  stand  for  12  hours 
under  a  bell  jar.  The  phosphoric  acid  contained  in  the  liquor  is 
separated  as  ammonium  magnesium  phosphate.  It  is  collected 
upon  a  small  filter,  washed  with  a  little  ammoniacal  water,  redis- 
solved,  and  titrated  with  the  uranium  solution  in  the  manner  al- 
ready indicated. 

Example. — The  following  is  an  example  of  this  kind  of  a  de- 
termination : 

(1)  One  and  one-half  grams  of  the  superphosphate  and  dis- 
tilled water  enough  to  make  150  cubic  centimeters. 

(2)  Filter  paper   with   reverted  phosphates,   60   cubic   centi- 
meters of  ammonium  citrate,  and  a  sufficient  quantity  of  distilled 
water  to  make  150  cubic  centimeters. 

Aqueous  solution  (i)    25  cc.    j  =  f  the          le< 

Citrate  solution        (2)    25  cc.    ) 

Add  magnesium  solution  20  cubic  centimeters  and  ammonia 
in  excess,  and  allow  from  12  to  24  hours  of  digestion,  then  filter 
and  wash,  dissolve  and  titrate. 

Required  of  solution  of  uranium  8.55  cubic  centimeters  (i  cubic 
centimeter = 5  milligrams  P2O5). 

Correction,  0.20  to  be  deducted=8-35  cubic  centimeters. 

8.35X0.005=0.04175  gram  P2Or,  for  0.25  gram  of  the  sample. 
Then  0.04 175 -=-0.25 =16.7  per  cent. 

From  the  above  data  there  would  be  16.7  per  cent,  of  phos- 
phoric acid  soluble  in  water  and  in  ammonium  citrate. 

If  it  be  desirable  to  have  separately  the  phosphoric  acid  soluble 
in  water,  a  separate  precipitation  is  made  of  the  aqueous  solution 
alone  by  means  of  the  magnesium  citrate  solution.  The  precipi- 
tate washed  with  ammoniacal  water  is  redissolved  and  titrated  in 
the  manner  indicated. 

In  subtracting  from  the  figures  obtained  with  the  two  solutions 
together  the  number  obtained  for  the  phosphoric  acid  soluble  in 
water,  the  number  representing  the  phosphoric  acid  soluble  in 
ammonium  citrate  alone,  is  obtained. 


THE    AMMONIO-MANGANOUS   METHOD  151 

It  is  to  be  noted  that  the  determinations  with  uranium  require 
always  two  successive  titrations.  It  would  therefore  be  an  ad- 
vantage in  all  operations  to  precipitate  a  weight  of  ammonium 
magnesium  phosphate  sufficient  for  allowing  this  precipitate  to  be 
dissolved  and  made  up  to  100  cubic  centimeters,  on  which  amount 
it  would  be  possible  to  execute  two,  three  or  four  determinations, 
and  thus  to  obtain  a  result  of  great  accuracy. 

138.  Conclusions. — It  has  been  seen  from  the  above  data  that 
the  French  chemists  have  worked  out  the  uranium  volumetric 
method  with  great  patience  and  attention  to  detail.    Where  many 
determinations  are  to  be  made  it  is  undoubtedly  possible  for  an 
analyst  to  reach  a  high  degree  of  accuracy  as  well  as  to  attain  a 
desirable  rapidity  by  using  this  method.     For  a  few  determina- 
tions, however,  the  labor  of  preparing  and  setting  the  standard 
solutions  required  would  be  far  greater  than  the  actual  determina- 
tions either  by  the  molybdate  or  citrate  gravimetric  methods.    For 
control  work  in  factories  and  for  routine  work  connected  with  fer- 
tilizer inspection,  the  method  has  sufficient  merit  to  justify  a  com- 
parison with  the  processes  already  in  use  by  the  official  chemists 
of  this  country. 

The  use  of  an  alkaline  ammoniacal  citrate  solution,  however, 
for  the  determination  of  reverted  acid  renders  any  comparison  of 
the  French  method  with  our  own  impossible.  On  the  other  hand, 
the  French  method  for  water-soluble  acid  is  based  on  the  same 
principle  as  our  own ;  viz.,  washing  at  first  with  successive  small 
portions  of  water,  and  thus  avoiding  the  decomposition  of  the 
soluble  phosphates,  which  is  likely  to  occur  when  too  great  a  vol- 
ume of  water  is  added  at  once. 

In  the  matter  of  the  temperature  and  time  as  affecting  the  sol- 
ubility of  reverted  acid,  the  French  method  is  also  distinctly  in- 
ferior to  our  own.  The  digestion  is  allowed  to  continue  from 
12  to  24  hours,  at  the  pleasure  of  the  analyst,  and  meanwhile  it 
is  subjected  to  room  temperature.  It  is  not  difficult  to  see  that 
this  treatment  in  the  same  sample  would  easily  yield  disagreeing 
results  between  12  hours  at  a  winter  temperature  and  24  hours  at 
summer  heat. 

139.  The  Ammonio-Manganous  Method. — The  principle  of  this 


152  AGRICULTURAL   ANALYSIS 

process  is  based  on  the  separation  of  the  phosphoric  acid  as  the 
ammonio-manganous  salt  and  the  subsequent  oxidation  of  the 
manganese  to  peroxid  acid.12  The.  quantity  of  the  peroxid  is  de- 
termined by  the  titration  with  hyposulfite  of  soda  of  the  iodin 
liberated  from  potassium  iodid.  After  a  study  of  the  methods  of 
preparing  the  ammonio-manganous  salt  according  to  the  proced- 
ures of  Otto,  Heintz  and  Gibbs,  the  following  process  was  adopted 
as  the  most  suitable :  To  50  cubic  centimeters  of  a  solution  of  so- 
dium phosphate,  containing  about  100  milligrams  of  phosphoric 
acid,  are  added  10  cubic  centimeters  of  a  20  per  cent,  solution  of 
ammonium  chlorid,  10  cubic  centimeters  of  ammonia,  25  cubic 
centimeters  of  a  solution  of  ammonium  citrate  (150  grams  citric 
acid,  500  cubic  centimeters  ammonia  and  1000  cubic  centimeters 
water),  an  excess  of  a  manganous  salt,  and  25  cubic  centimeters 
of  a  2.5  per  cent,  solution  of  magnesium  sulfate. 

This  mixture  shows  an  immediate  yellow  coloration,  increasing 
little  by  little  to  a  greenish  brown,  but  preserves  its  complete  lim- 
pidity. After  24  hours  the  sides  of  the  vessel  are  found  coated 
with  colorless  brilliant  crystals  of  ammonio-manganous  phosphate, 
but  even  after  several  days  the  separation  of  the  phosphoric  acid 
is  not  complete. 

If  the  reagents  employed  be  hot,  a  different  series  of  phenomena 
are  presented.  The  yellowish  color  at  first  more  pronounced,  soon 
disappears  and  while  the  liquid  is  boiling,  if  it  be  stirred  without 
striking  the  walls  of  the  vessel,  there  are  immediately  separated 
brilliant  crystals  of  the  salt  of  a  pale  rose  color.  At  the  end  of 
a  few  minutes  the  total  phosphoric  acid  is  precipitated.  The 
analysis  is  conducted  as  follows :  After  covering  the  liquid,  in 
which  the  phosphoric  acid  has  been  separated  as  above  described, 
the  contents  of  the  vessel  are  thrown  on  a  filter  and  the  precipitate 
washed  with  100  cubic  centimeters  of  a  dilute  solution  of  ammo- 
nium chlorid  (0.5  per  cent.).  The  filtration  and  washing  should  be 
made  rapidly  to  avoid  danger  of  solution  of  the  crystals,  and  the 
whole  operation  should  last  only  a  few  minutes. 

Insoluble  phosphates  are  first  dissolved  in  an  acid  and  the  phos- 
phoric acid  thrown  out  by  ammonium  molybdate,  the  yellow 

"  Lindeman  and    Motteu,   Bulletin  de  la  Societe*  chimique   de  Paris, 
1895.  [3],  13  :523- 


PEMBERTON'S  VOLUMETRIC  METHOD  153 

precipitate  is  dissolved  in  ammonia,  and  the  solution  treated  as 
above. 

The  crystals  of  ammonio-manganous  phosphate  are  dissolved 
in  dilute  hydrochloric  acid,  the  solution,  diluted  to  300  cubic  centi- 
meters, treated  with  from  one  to  three  cubic  centimeters  of  hydro- 
gen peroxid,  20  cubic  centimeters  of  a  10  per  cent,  solution  of 
potassium  hydroxid  added  and  boiled  for  some  time  to  expel  an 
excess  of  the  peroxid. 

After  cooling,  20  cubic  centimeters  of  20  per  cent,  hydrochloric 
acid  are  added  and  the  solution  allowed  to  stand  for  some  time  in 
order  to  destroy  any  traces  of  an  alkaline  peroxid.  After  the  ad- 
dition of  20  cubic  centimeters  of  a  10  per  cent,  solution  of  potas- 
sium iodid,  the  liberated  iodin  is  titrated  by  a  set  solution  of 
sodium  hyposulfite.  The  reactions  which  take  place  in  these 
operations  are  illustrated  by  the  following  equations  :  The  hydro- 
gen peroxid  converts  the  manganous  salt  into  the  compound 
MngOi^sMnO-jMnO.  The  ammonio-manganous  phosphate  has 
the  composition  6NH4MnPO4.  When  oxidized  by  hydrogen 
peroxid,  it  yields  three  molecules  of  phosphoric  anhydrid, -3P2O5,- 
and  one  molecule  of  the  compound  5MnO2MnO.  When  the 
manganic  peroxid  is  treated  with  potassium  iodid  the  reaction  is : 
5MnO2+2OHCl+ ioKI=5MnCl,+  ioKCl+ioI,  and  ioI+ioNaa 
S,O3  =  sNa2S4O6  +  loNal.  Then  ioNa,S2O3  =  10!  =  3P,2O5. 
From  these  data  the  percentage  of  P2O5  is  readily  calculated. 

The  method  is  of  interest  from  the  principle  involved,  but  is  of 
little  practical  value  because  of  the  necessity  of  separating  the 
phosphoric  acid  from  all  insoluble  phosphates  by  the  molybdate 
method.  The  authors  have  endeavored  to  avoid  this  separation 
and  express  the  hope  that  a  direct  way  may  be  found. 

THE  DETERMINATION    OF    PHOSPHORIC   ACID  BY  TITRA- 
TION  OF  THE  YELLOW   PRECIPITATE 

140.  Pemberton's  Volumetric  Method. — In  order  to  shorten  the 
work  of  determining  the  phosphoric  acid,  numerous  attempts  have 
been  made  to  execute  the  final  determination  directly  on  the  yel- 
low precipitate  obtained  by  treating  a  solution  of  a  phosphate 
with  ammonium  molybdate  in  nitric  acid.  The  composition  of 
this  precipitate  appears  to  be  somewhat  variable,  and  this  fact 


154  AGRICULTURAL   ANALYSIS 

has  cast  doubt  on  the  methods  of  determination  based  on  its 
weight.  Its  most  probable  composition  is  expressed  by  the  fol- 
lowing formula,  (NH4)3PO4(MoO3)12.  For  convenience  in 
writing  reactions  this  formula  should  usually  be  doubled.  Pem- 
berton  has  described  a  volumetric  determination  of  phosphoric  acid 
in  the  yellow  precipitate  which  is  easily  conducted  and  is  very 
rapid.13 

The  method  as  originally  proposed  by  Pemberton  has  not  al- 
ways given  satisfactory  results  when  compared  with  the  molyb- 
date  gravimetric  process,  but  as  perfected  by  experience  has  con- 
stantly grown  in  favor  until  now  it  is  regarded  as  entirely  trust- 
worthy on  account  of  its  original  merit  and  of  the  extended  use 
in  later  forms.  It  has,  however,  attracted  so  much  attention  from 
analysts  as  to  the  principles  of  the  original  process,  that  they  are 
given  in  some  detail. 

141.  The  Process. — The  principle  of  the  process  is  based  on  the 
separation  of  the  phosphoric  acid  as  ammonium-phosphomolyb- 
date,  freeing  the  yellow  precipitate  from  any  free  nitric  acid  by 
washing,  dissolving  the  yellow  precipitate  in  an  excess  of  standard 
alkali  and  titrating  the  residual  alkali  by  a  standard  acid.  The 
process  as  originally  described  by  Pemberton  is  carried  out  as 
follows :  One  gram  of  phosphate  rock,  or  from  two  to  three 
grams  of  phosphatic  fertilizer,  are  dissolved  in  nitric  acid  and, 
without  evaporation,  diluted  to  250  cubic  centimeters.  Without 
filtering,  25  cubic  centimeters  are  placed  in  a  four-ounce  beaker 
and  ammonia  added  until  a  slight  precipitate  begins  to  form. 
Five  cubic  centimeters  of  nitric  acid  of  one  and  four-tenths 
specific  gravity  are  added,  and  10  cubic  centimeters  of  saturated 
solution  of  ammonium  nitrate  and  enough  water  to  make  the 
volume  about  65  cubic  centimeters .  The  contents  of  the 
beaker  are  boiled,  and  while  still  hot  five  cubic  centimeters  of  the 
aqueous  solution  of  ammonium  molybdate  added.  Additional 
quantities  of  the  molybdate  are  used,  if  necessary,  until  the 
whole  of  the  phosphorus  pentoxid  is  thrown  out. 

After  allowing  to  settle  for  a  moment  the  contents  of  the  beaker 
are  poured  upon  a  filter  seven  centimeters  in  diameter.  The  pre- 
u Journal  of  the  American  Chemical  Society,  1893,  15  :  382. 


THE   PROCESS  ,  155 

cipitate  is  thoroughly  washed  with  water,  both  by  decantation 
and  on  the  filter.  The  filter  with  its  precipitate  is  transferred  to 
a  beaker  and  dissolved  with  an  excess  of  standard  alkali  in  the 
presence  of  phenolphthalein.  The  residual  alkali  is  determined 
by  titration  with  standard  acid.  Each  cubic  centimeter  of  alkali 
employed  should  correspond  to  one  milligram  of  phosphorus  pent- 
oxid  (P2O5). 

The  reagents  have  the  composition  indicated  below : 

Ammonium  Molybdate. — Ninety  grams  of  the  crystals  of  am- 
monium molybdate  are  placed  in  a  large  beaker  and  dissolved  in 
a  little  less  than  one  liter  of  water.  The  beaker  is  allowed  to  stand 
over  night  and  the  clear  liquor  decanted.  Any  undissolved  acid 
is  brought  into  solution  in  a  little  ammonia  water  and  added  to 
the  clear  liquor.  If  a  trace  of  phosphoric  acid  be  present  a  little 
magnesium  sulfate  is  added  and  enough  ammonia  to  produce  a 
slight  alkaline  reaction.  The  volume  of  the  solution  is  then 
made  up  to  one  liter.  It  is  to  be  observed  that  nitric  acid  is  not 
used  in  the  preparation  of  this  reagent,  which  is  known  as  the 
aqueous  solution.  Each  cubic  centimeter  of  this  solution  is  capa- 
ble of  precipitating  three  milligrams  of  phosphorus  pentoxid. 

Standard  Potassium  Hydroxid. — This  solution  is  made  of  such 
strength  that  one  cubic  centimeter  is  equivalent  to  one  milli- 
gram of  phosphorus  pentoxid.  Treated  with  acid  of  normal 
strength,  100  cubic  centimeters  are  required  to  neutralize  32.65 
cubic  centimeters  thereof.  The  strength  of  the  solution  can  not 
be  safely  assumed  from  the  weight  and  purity  of  the  material,  but 
is  to  be  ascertained  by  comparison  with  a  solution  of  a  phosphate 
of  known  composition. 

Standard  Acid. — This  should  have  the  same  strength,  volume 
for  volume,  as  the  standard  alkali  solution.  It  is  made  by  dilut- 
ing 326.5  cubic  centimeters  of  normal  nitric  acid  to  one  liter. 

Ammonium  Nitrate. — A  saturated  aqueous  solution  of  the  salt 
is  used. 

Indicator. — The  indicator  to  be  used  is  an  alcoholic  solution  of 
phenolphthalein,  one  gram  in  100  cubic  centimeters  of  60  per 
cent,  alcohol,  and  half  a  cubic  centimeter  of  this  should  be  used 
for  each  titration. 


156  AGRICULTURAL   ANALYSIS 

Thomson  has  shown  that  of  the  three  hydrogen  atoms  in 
phosphoric  acid,  two  must  be  saturated  with  alkali  before  the 
reaction  with  phenolphthalein  is  neutral.14  Therefore,  when  the 
yellow  precipitate  is  broken  up  by  an  alkali,  according  to  the 
reaction  to  follow,  only  four  of  the  six  molecules  of  ammonium 
are  required  to  form  a  neutral  ammonium  phosphate  as  determined 
by  the  indicator  employed.  The  remaining  two  molecules  of 
ammonium  unite  with  the  molybdenum,  forming  also  a  salt  neu- 
tral to  the  indicator. 

Phenolphthalein  is  preferred  because,  as  has  been  shown  by 
Long,  its  results  are  reliable  in  the  presence  of  ammonium  salts 
unless  they  be  present  in  large  quantity,  and  if  the  solution  be 
cold  and  the  indicator  be  used  in  sufficient  quantity.15  To  pre- 
pare the  indicator  for  this  work,  one  gram  of  phenolphthalein  is 
dissolved  in  100  cubic  centimeters  of  60  per  cent,  alcohol.  At 
least  one-half  of  a  cubic  centimeter  of  the  solution  is  used  for 
each  titration. 

The  advantages  claimed  for  the  method  are  its  speed  and 
accuracy.  Much  time  is  saved  by  avoiding  the  necessity  for  the 
removal  of  the  silica  by  evaporation.  The  results  of  analyses 
with  and  without  the  removal  of  the  silica  are  practically  identical. 
When  the  silica  is  not  removed  it  is  noticed  that  the  filtrate 
from  the  yellow  precipitate  has  a  yellow  tint. 

The  reaction  is  represented  by  the  following  formula : 

(NH4)6(P04)2(Mo03)24-4-46KOH=(NH4)4(HP04)2+ 
(NH4)2MoO4-r-23K2MoO4-f22H2O. 

From  this  reaction  it  is  seen  that  the  total  available  acidity  of 
one  molecule  of  the  yellow  precipitate  titrated  against  phenol- 
phthalein is  equivalent  to  23  molecules  of  potassium  hydroxid. 

Calculation  of  Results. — The  standard  alkali  is  of  such  strength 
that  one  cubic  centimeter  is  equal  to  one  per  cent,  of  phosphoric 
acid  when  one  gram  of  material  is  employed  and  one-tenth  of  it 
taken  for  each  determination.  If  in  a  given  case  one  gram  of  a 
sample  and  one-tenth  of  the  solution  are  used,  and  50  cubic  cen- 
timeters of  alkali  added  to  the  yellow  precipitate,  it  requires 

14  Chemical  News,  1883,  47  :  127,  186. 

15  American  Chemical  Journal,  1889,  11  :  84. 


THE    PROCESS  157 

32  cubic  centimeters  of  standard  alkali  to  neutralize  the  excess 
of  acid. 

The  alkali  consumed  by  the  yellow  precipitate  represents  50 — 32 
=  18  cubic  centimeters.  The  sample,  therefore,  contains  18  per 
cent,  of  phosphoric  acid. 

Comparison  with  Official  Method. — A  comparison  of  the  Pem- 
berton  volumetric  with  the  official  method  of  the  Association  of 
Official  Agricultural  Chemists  has  been  made  by  Day  and  Bry- 
ant.16 The  comparisons  were  made  on  samples  containing  from 
1.45  to  37.28  per  cent,  of  phosphoric  acid  and  resulted  as  follows: 

Percent.  Percent. 

Substance.  PjO5,  Official.  P»O6,  Pemberton. 

No.  i.   Florida  rock 1.45  1.32 

"2.        "          "      440  4-53 

"    3.  Sodium  phosphate 19.78  *9-99 

"    4-        "                  "         I9-72  19-73 

"    5.  Florida  rock 37-28  37-22 

This  near  agreement  shows  the  reliability  of  the  method.  The 
comparison  of  the  Pemberton  volumetric  method  with  the  official 
gravimetric  method  was  investigated  by  Kilgore,  reporter  of  the 
Association  of  Official  Agricultural  Chemists,  in  i894.17  The 
individual  variations  were  found  to  be  greater  than  in  the  regular 
method,  but  the  average  results  were  nearly  identical  therewith. 
The  method  works  far  better  with  small  percentages  of  phosphoric 
acid  than  with  large.  Where  the  average  of  the  results  by  the 
official  methods  gave  12.25  Per  cent.,  the  volumetric  process  gave 
11.90  per  cent.,  whereas  in  the  determination  of  a  smaller  per- 
centage the  results  were  2.72  and  2.73  per  cent.,  respectively. 
Kilgore  proposes  a  variation  of  the  method  which  differs  from 
the  original  in  two  principal  points.18  First,  the  temperature  of 
precipitation  in  the  Pemberton  process  is  100° ;  but  in  the  modi- 
fied form  from  55°  to  60°.  At  the  higher  temperature  there  is 
•danger  of  depositing  molybdic  acid. 

The  second  difference  is  in  the  composition  of  the  molybdate 
solution  employed.  The  official  molybdate  solution  contains  about 

16  Journal  of  the  American  Chemical  Society,  1894,  16  :  282. 

17  Division  of  Chemistry,  Bulletin  43,  1894  :  68. 

18  Division  of  Chemistry,  Bulletin  43,  1894  :  91. 


158  AGRICULTURAL  ANALYSIS 

60  grams  of  molybdenum  trioxid  in  a  liter,  while  the  Pem- 
berton  solution  contains  66  grams.  There  is,  therefore, 
not  much  difference  in  strength.  The  absence  of  nitric  acid,  how- 
ever, from  the  Pemberton  solution  favors  the  deposition  of  the 
molybdic  acid  when  heat  is  applied. 

Kilgore,  therefore,  conducts  the  analysis  as  follows:  The 
solution  of  the  sample  is  made  according  to  the  official  nitric  and 
hydrochloric  acid  method  for  total  phosphoric  acid.  For  the 
determination,  20  to  40  cubic  centimeters  are  used  corresponding 
to  two-tenths  or  four-tenths  gram  of  the  sample.  Am- 
monia is  added  until  a  slight  precipitate  is  produced  and  the 
volume  is  then  made  up,  with  water,  to  75  cubic  centi- 
meters. Add  some  ammonium  nitrate  solution,  from  10  to  15 
cubic  centimeters,  but  this  addition  is  not  necessary  unless 
much  of  the  nitric  acid  has  been  driven  off  during  solution.  Heat 
in  the  water  bath  to  60°  and  precipitate  with  some  freshly  filtered 
official  molybdate  solution.  Allow  to  stand  for  five  minutes,  filter 
as  quickly  as  possible,  wash  four  times  by  decantation,  using  from 
50  to  75  cubic  centimeters  of  water  each  time,  and  then  wash 
on  a  filter  until  all  acid  is  removed.  The  solution  and  titra- 
tion  of  the  yellow  precipitate  are  accomplished  as  in  the  Pem- 
berton method.  The  agreement  of  the  results  obtained  by  this- 
modified  method  was  much  closer  with  the  official  gravimetric 
method  than  those  obtained  by  the  Pemberton  process. 

142.  Investigations  of  the  Volumetric  Method  by  the  Asso- 
ciation of  Official  Agricultural  Chemists. — The  great  value  of  the 
volumetric  method  by  reason  of  the  saving  of  time  in  analytical 
work,  especially  where  great  numbers  of  analyses  are  to  be  made, 
led  to  a  painstaking  investigation  of  its  reliability  and  agreement 
with  the  gravimetric  process  on  the  part  of  the  official  chemists. 
The  results  of  these  investigations  are  published  in  detail  in  the 
proceedings  of  the  association.10 

19  Division  of  Chemistry,  Bulletin  47,  1896    :  70. 
Division  of  Chemistry,  Bulletin  49,  1897  :  60. 
Division  of  Chemistry,  Bulletin  51,  1898  147. 
Division  of  Chemistry,  Bulletin  56,  1899  :  36. 
Division  of  Chemistry,  Bulletin  57,  1899  :  69. 
Division  of  Chemistry,  Bulletin  62,  1901  :  35. 
Bureau  of  Chemistry,  Bulletin  67,  1902  :  22. 
Bureau  of  Chemistry,  Bulletin  8r,  1904  :  164. 


OPTIONAL   VOLUMETRIC    METHOD  159 

These  investigations  have  led  to  the  adoption  of  the  volumetric 
method  in  the  present  form,  and  established  its  position  as  a  pro- 
cess which  can  be  relied  upon  to  give  concordant  and  reliable  re- 
sults. For  all  ordinary  analytical,  routine  and  control  work  it  may 
be  confidently  used.  In  cases  of  controversy,  and  especially  be- 
fore the  courts,  it  is  advisable  to  check  the  data  obtained  by  the 
volumetric  method  against  the  results  of  the  official  gravimetric 
•determination.  The  principal  credit  for  perfecting  this  method 
is  due  to  Kilgore,  as  is  clearly  shown  by  a  study  of  the  references 
.given. 

143.  Optional  Volumetric  Method. — The  principles  on  which  this 
rapid  and  accurate  process  is  based  have  been  described  in  detail 
in  the  discussion  of  the  Pemberton  process.  The  method  of  con- 
ducting the  determination  and  the  reagents  employed  as  prescribed 
by  the  official  chemists  are  as  follows : 

Reagents  Used:  Molybdic  Acid. — To  100  cubic  centimeters  of 
the  molybdic  acid  solution  used  in  the  official  gravimetric  method 
already  described,  add  five  cubic  centimeters  of  nitric  acid  of  1.42 
specific  gravity.  If  cloudy  this  solution  should  be  filtered  before 
using. 

Potassium  or  Ammonium  Nitrate  Solution. — Dissolve  three 
grams  of  the  salt  in  100  cubic  centimeters  of  water. 

Nitric  Acid. — Dilute  100  cubic  centimeters  of  nitric  acid  of  1.42 
•specific  gravity  to  1000  cubic  centimeters  with  water. 

Potassium  Hydro.vid. — This  solution  contains  18.171  grams  of 
KOH  in  one  liter.  It  is  prepared  by  diluting  323.81  cubic  centi- 
meters of  a  normal  solution  of  pure  potassium  hydroxid,  free  of 
carbonates,  to  one  liter.  One  milligram  of  the  solution  is  equiva- 
lent to  one  milligram  of  phosphorus  pentoxid. 

Standard  Nitric  Acid  Solution. — The  strength  of  this  solution 
is  the  same  as,  or  one-half  that  of,  the  standard  alkali  solution, 
and  is  determined  by  titrating  against  that  solution,  using  phenol- 
phthalein  as  indicator. 

Phenolphthalein  Solution. — One  gram  of  phenolphthalein  is 
dissolved  in  100  cubic  centimeters  of  alcohol. 

Total  Phosphoric  Acid.  Methods  of  Making  Solution. — Dis- 
rsolve  according  to  the  official  methods  described  in  paragraph  61, 


160  AGRICULTURAL   ANALYSIS 

preferably  method  5,  when  these  acids  are  a  suitable  solvent, 
and  dilute  to  200  cubic  centimeters  with  water. 

Determination. — For  percentages  of  phosphoric  acid  of  five  or 
below  use  an  aliquot  corresponding  to  0.4  gram  substance ;  for 
percentages  between  five  and  20  use  an  aliquot  corresponding  to 
0.2  gram  substance ;  and  for  percentages  above  20  use  an  aliquot 
corresponding  to  o.i  gram  substance.  Add  from  five  to  10  cubic 
centimeters  of  nitric  acid,  depending  on  the  method  of  solution 
(or  the  equivalent  in  ammonium  nitrate),  nearly  neutralize  with 
ammonia,  dilute  to  from  75  to  100  cubic  centimeters,  heat  in  a 
water  bath  to  from  60°  to  65°,  and 'for  percentages  below  five 
add  from  20  to  25  cubic  centimeters  of  freshly  filtered  molybdic 
solution.  For  percentages  between  five  and  20  add  from  30  to 
35  cubic  centimeters  molybdic  solution;  stir,  let  stand  about  15 
minutes,  filter  at  once',  wash  once  or  twice  with  water  by  decanta- 
tion,  using  from  25  to  30  cubic  centimeters  each  time,  agitating 
the  precipitate  thoroughly  and  allowing  it  to  settle;  transfer  to 
filter  and  wash  five  or  six  times,  using  enough  water  to  make 
with  the  decantation  washings  about  200  cubic  centimeters. 
Transfer  precipitate  and  filter  to  beaker  or  precipitating  vessel, 
dissolve  in  small  excess  of  standard  alkali,  add  a  few  drops  of 
phenolphthalein  solution  and  titrate  excess  of  alkali  with  stand- 
ard acid  (nitric). 

Water-Soluble  Phosphoric  Acid. — Dissolve  the  soluble  acid  ac- 
cording to  directions  given  under  the  official  method  for  the  grav- 
imetric determination  of  water-soluble  acid,  paragraph  67.  To  an 
aliquot  portion  of  the  solution  corresponding  to  0.2  or  0.4  gram, 
add  10  cubic  centimeters  of  concentrated  nitric  acid  and  then  am- 
monia until  a  slight  precipitate  is  formed,  dilute  to  60  cubic 
centimeters,  and  proceed  as  above  described. 

Citrate-Insoluble  Phosphoric  Acid. —  (a)  In  Acidulated  Sam- 
ples.— Heat  100  cubic  centimeters  of  strictly  neutral  ammonium 
citrate  solution  of  1.09  specific  gravity  to  65°  in  a  flask  placed  in 
a  bath  of  warm  water,  keeping  the  flask  loosely  stoppered  to  pre- 
vent evaporation.  When  the  citrate  solution  in  the  flask  has 
reached  65°,  drop  into  it  the  filter  containing  the  washed  residue 
from  the  water-soluble  phosphoric  acid  determination,  stopper 


ALKALIMETRIC  ESTIMATION  l6l 

tightly  with  a  smooth  rubber,  and  shake  violently  until  the  filter 
paper  is  reduced  to  a  pulp.  Place  the  flask  in  the  bath  and  main- 
tain it  at  such  a  temperature  that  the  contents  of  the  flask  will 
stand  at  exactly  65°.  Shake  the  flask  every  five  minutes.  At  the 
expiration  of  exactly  30  minutes  from  the  time  the  filter  and 
residue  are  introduced,  remove  the  flask  from  the  bath  and  im- 
mediately filter  the  contents  as  rapidly  as  possible.  Wash  thor- 
oughly with  water  at  65°.  Transfer  the  filter  and  its  contents  to 
a  crucible,  ignite  until  all  organic  matter  is  destroyed,  add  from 
10  to  15  cubic  centimeters  of  strong  hydrochloric  acid,  and  digest 
until  all  phosphate  is  dissolved ;  or  return  the  filter  with  contents 
to  the  digestion  flask,  add  from  30  to  35  cubic  centimeters  strong 
nitric  acid,  from  five  to  10  cubic  centimeters  strong  hydrochloric 
acid,  and  boil  until  all  phosphate  is  dissolved.  Dilute  the  solution 
to  200  cubic  centimeters.  If  desired,  the  filter  and  its  contents 
may  be  treated  according  to  the  methods  in  paragraph  61  under 
methods  of  solution.  Mix  well ;  filter  through  a  dry  filter ;  take 
a  definite  portion  of  the  filtrate  and  proceed  as  under  total  phos- 
phoric acid. 

(6)  In  Non-Acidulated  Samples. — In  case  a  determination  of 
citrate-insoluble  phosphoric  acid  is  required  in  non-acidulated 
samples  it  is  to  be  made  by  treating  two  grams  of  the  phosphatic 
material,  without  previous  washing  with  water,  precisely  in  the 
way  above  described,  except  that  in  case  the  substance  contains 
much  animal  matter  (bone,  fish,  etc.)  the  residue  insoluble  in 
ammonium  citrate  is  to  be  treated  by  one  of  the  processes  de- 
scribed under  methods  of  solution,  paragraph  61. 

Citrate-Soluble  Phosphoric  Acid. — The  sum  of  the  water-solu- 
ble and  citrate-insoluble  subtracted  from  the  total  gives  the  cit- 
rate-soluble phosphoric  acid. 

144.  Alkalimetric  Estimation  of  Phosphoric  Acid  in  Connection 
with  the  Incineration  by  Acid  Mixture. — Neumann  recommends 
the  following  process,  which  is  a  variation  of  the  ordinary  volu- 
metric method  in  common  use  in  this  country  for  the  estimation 
of  phosphoric  acid  in  organic  matters  which .  have  been  incin- 
erated by  the  wet  acid  method  described  by  him.20  For  carrying 
10  Zeitschrift  fiir  physiologische  Chemie,  1902-3,  37  :  115. 


1 62  AGRICULTURAL   ANALYSIS 

out  this  method  the  substance  is  incinerated  by  a  mixture  of  sul- 
furic  and  nitric  acids.  From  the  ash  solution  obtained  by  the 
method  described  the  phosphoric  acid  is  precipitated  in  the  usual 
manner  as  phosphomolybdate.  The  washed  precipitate  is  imme- 
diately dissolved  in  an  excess  of  one-half  normal  soda-lye  and  the 
excess  of  alkali  titrated  with  one-half  normal  sulfuric  acid,  after 
driving  off  the  ammonia  by  boiling  and  allowing  the  solution  to 
become  completely  cool. 

Since  each  molecule  of  the  phosphoric  pentoxid  (P2O5)  of  the 
yellow  precipitate  obtained  by  this  method  of  treatment  requires 
for  its  complete  neutralization,  with  the  use  of  phenolphthalein 
as  an  indicator,  56  molecules  of  NaOH,  so  each  cubic  centimeter 
of  one-half  normal  soda-lye  used  corresponds  to  1.268  milligrams 
of  P205. 

The  solutions  used  by  Neumann  are  as  follows : 

1 i )  50  per  cent,  ammonium  nitrate  solution. 

(2)  10  per  cent,  of  ammonium  molybdate  solution  (dissolved, 
cooled,  and  filtered). 

(3)  One-half  normal  potash  lye  and  one-half  normal  sulfuric 
acid. 

(4)  One  per  cent,  alcoholic  phenolphthalein  solution. 

The  substance  is  incinerated  according  to  the  method  described 
and  the  dilution  with  water,  which  is  recommended  at  the  close  of 
the  method,  as  well  as  the  boiling  of  the  ash  solution,  are  prop- 
erly modified  for  the  special  estimation  of  the  phosphoric  acid. 

Under  the  assumption  that  for  the  incineration  not  more  than 
40  cubic  centimeters  of  the  acid  mixture  have  been  used,  about  140 
cubic  centimeters  of  water  are  added  to  the  ash  solution,  so  that  in 
all  the  analyst  has  in  amount  from  150  to  160  cubic  centimeters. 
It  should  be  remembered  in  this  case  that  about  one-half  of  the 
acid  mixture  has  been  volatilized  during  the  incineration.  After 
the  addition  of  50  cubic  centimeters  of  ammonium  nitrate,  the 
mixture  is  heated  to  from  70°  to  80°  until  bubbles  begin  to 
ascend  through  the  liquid.  Thereupon,  40  cubic  centimeters  of 
ammonium  molybdate  are  added.  This  quantity  is  sufficient  for 
at  least  60  milligrams  of  P2O0.  It  is  recommended  that  the  quan- 


ALKALIMBTRIC  ESTIMATION  163 

tity  of  substance  used  be  so  chosen  that  it  contains  not  more  than 
50  milligrams  of  phosphoric  acid.  If  more  than  40  cubic  centi- 
meters of  the  acid  mixture  have  been  used  in  the  incineration,  then 
the  quantity  of  water  added  in  the  dilution  and  the  quantity  of 
ammonium  nitrate  therein  should  be  proportionately  increased. 

The  flask  containing  the  precipitate  is  vigorously  shaken  for  a 
half  minute,  by  which  process  the  precipitate  becomes  more 
granular,  and  it  is  then  allowed  to  stand  at  rest  for  15  min- 
utes. The  filtering  and  washing  are  carried  on  by  decantation. 
Thin,  ash-free  filter  paper  is  used,  which  on  the  subsequent  solu- 
tion of  the  precipitate  in  dilute  soda-lye  is  easily  torn  and  the  par- 
ticles of  which  are  evenly  divided  throughout  the  liquid.  The 
filter  paper,  which  has  a  diameter  of  from  five  to  six  centimeters, 
may  be  used  either  as  a  folded  filter  or  as  a  smooth  filter  in  a 
fluted  funnel.  Before  filtration  the  filter  is  filled  with  ice-cold 
water,  in  order  to  draw  the  filter  pores  together  and  to  prevent 
the  first  portions  of  the  solution,  which  is  still  warm,  from  run- 
ning through  cloudy.  In  order  to  conveniently  decant  the  super- 
natant liquid,  the  flask  is  laid  upon  the  ring  of  the  stand  some- 
what higher  than  the  filter  and  the  neck  is  drawn  down  in  such 
a  way  that  the  clear  liquid  runs  without  intermission  upon  the 
filter.  In  this  way  only  a  very  small  quantity  of  the  precipitate 
is  collected  upon  the  filter,  which  is  always  kept  about  two-thirds 
full.  The  washing  of  the  precipitate  is  conducted  with  about 
150  cubic  centimeters  of  ice-cold  water,  which  is  thoroughly  in- 
corporated with  the  precipitate,  and  after  standing  is  poured 
through  the  filter  in  the  way  described.  The  decantation  is  con- 
tinued with  repeated  washing  with  water  until  the  wash-water 
no  longer  gives  an  acid  reaction  with  litmus  paper.  The  washed 
filter  and  its  contents  are  then  put  back  in  the  flask  containing  the 
principal  part  of  the  precipitate,  150  cubic  centimeters  of  water 
added,  the  filter  broken  up  by  vigorous  shaking,  and  the  precipi- 
tate dissolved  by  adding  a  measured  portion  of  one-half  normal 
potash  lye  with  constant  shaking  and  without  warming.  It  is  then 
advisable  to  add  an  excess  of  from  five  to  six  cubic  centimeters 
of  one-half  normal  soda-lye  and  to  boil  the  solution  until  no 
longer  any  ammonia  is  evolved,  which  usually  requires  about 


164  AGRICULTURAL   ANALYSIS 

15  minutes  and  which  should  be  determined  by  testing  with 
moist  litmus  paper.  After  complete  cooling,  from  six  to  eight 
drops  of  the  phenolphthalein  solution  are  added  and  the  excess 
of  alkali  titrated  with  one-half  normal  sulfuric  acid. 

Calculation. — The  number  of  added  cubic  centimeters  of  one- 
half  normal  soda-lye,  after  the  subtraction  of  the  number  of  cubic 
centimeters  of  one-half  normal  acid  used,  multiplied  by  1.268, 
gives  the  quantity  of  P2O5  in  milligrams. 

145.  Comparison  of  the  Methods  of  Weighing  and  Titrating 
the  Yellow  Precipitate. — Baxter  gives  the  result  of  his  experi- 
ments upon  the  estimation  of  phosphoric  acid  by  weighing  the 
yellow  precipitate  after  heating  to  300°  and  also  by  titration  with 
standard  alkali.21 

In  securing  the  yellow  precipitate  in  a  form  sufficiently  pure 
for  analytical  purposes  he  states  that  it  can  not  be  washed  with 
water  owing  to  decomposition.  Ten  per  cent,  ammonium  nitrate 
solution  is  therefore  used  as  a  wash,  but  no  data  are  given  to 
prove  that  washing  was  carried  to  the  complete  removal  of  the 
molybdate.  Indeed,  all  the  results  show  that  the  precipitate  still 
contains  considerable  quantities  of  ammonium  molybdate  or 
molybdenum  oxid.  It  is  stated  that  the  formula  of  the  precipi- 
tate washed  with  the  ammonium  nitrate  solution  and  dried  at  300° 
is  (NH4)3PO4.i2MoO3,  but  owing  to  the  occlusion  of  molyb- 
dic  acid  the  theoretical  percentage  of  P2O5  (3.783)  is  never  ob- 
tained. The  precipitate  only  contains  3.742  per  cent,  of  phos- 
phoric acid. 

In  the  second  article  evidence  is  given  to  show  that  the  washed 
unheated  yellow  precipitate  has  the  formula  (NH4)2HPO4.~ 
i2MoO3,  and  that  the  quantity  of  hydroxid  required  in  titration 
corresponds  much  more  nearly  to  48  molecules  than  to  46  mol- 
ecules for  each  molecule  of  phosphorus  pentoxid.  Owing  to  the 
occlusion  of  some  molybdic  acid  the  author  gives  the  following 
exact  formula  as  that  of  the  unheated  washed  yellow  precipitate 
actually  obtained  in  analytical  work — (NH4)2HPO4.i2.i43MoO3. 

Attention  is  also  called  to  the  fact  that  the  composition  of  the 
precipitate  is  more  constant  and  the  results  more  reliable  when 
11  American  Chemical  Journal,  1902,  28  :  298 ;  1905,  34  :  204. 


ESTIMATION   OF   PHOSPHORIC   ACID  165 

the  phosphate  solution  is  added  to  the  molybdic  solution  than 
the  reverse. 

There  is  a  number  of  other  minor  well  known  discoveries  in 
this  article  which  need  not  be  mentioned  here.  The  author  seems 
to  be  entirely  unaware  of  the  work  of  the  Association  of  Official 
Agricultural  Chemists  on  this  subject. 

The  conclusions  seem  to  be  applicable  to  the  conditions  under 
which  the  author  worked,  but  criticism  might  be  made  that  the 
precipitate  was  not  sufficiently  washed  in  any  of  the  experiments, 
and  further,  that  the  quantity  of  precipitate  is  very  much  larger 
than  it  is  customary  to  use  when  working  this  method,  weighing 
as  it  does  almost  three  grams.  The  value  of  all  the  work  de- 
pends on  the  washing  of  the  yellow  precipitate,  which,  as  has  been 
said,  was  incomplete,  and  no  evidence  is  given  to  show  that  im- 
purities could  not  have  been  entirely  removed. 

146.  Estimation  of  Phosphoric  Acid  as  a  Lead  Compound. 
— In  the  volumetric  lead  method,  as  described  by  Wavelet,  the 
phosphoric  acid  is  precipitated  by  the  magnesium  citrate  solu- 
tion as  in  the  uranium  method  of  Joulie,  as  practiced  by  the 
French  chemists,  and  the  washing  of  the  precipitate  and  its  solu- 
tion of  nitric  acid  are  also  conducted  as  in  that  method.22  After 
solution  in  nitric  acid,  ammonia  is  added  to  neutrality  and  the 
solution  is  then  made  acid  with  acetic.  The  phosphoric  acid  is 
precipitated  in  the  acid  solution  by  a  standard  solution  of  lead 
nitrate,  the  precipitate  having  the  formula  P2O53PbO. 

The  end  reaction  is  determined  by  placing  a  drop  of  the 
titrated  mixture  on  a  white  greased  dish  in  contact  with  a  drop 
of  a  five  per  cent,  solution  of  potassium  iodid.  When  all  the 
phosphoric  acid  is  precipitated,  the  least  excess  of  the  lead  salt 
is  revealed  by  the  characteristic  yellow  precipitate  of  lead  iodid. 

The  author  of  the  process  claims  that  the  lead  phosphate  is  in- 
soluble in  the  excess  of  acetic  acid,  and  that  the  phosphate  itself 
does  not  give  any  yellow  coloration  with  potassium  iodid.  The 
process  is  quite  as  exact  as  the  uranium  method  and  the  end 
reaction  is  far  sharper ;  the  standard  reagents  are  easily  made 
and  preserved.23  The  method  described  merits,  at  least,  a  com- 

21  Repertoire  de  Pharmacie,  1893  [3],  5  :  153. 

M  Revue  de  Chimie  analytique  applique"e,  1893,  1  :  113. 


1 66  AGRICULTURAL   ANALYSIS 

parative  trial  with  the  uranium  process,  but  can  not  be  recom- 
mended as  exact  until  further  approved  by  experience. 
The  reagents  employed  have  the  following  composition : 

(1)  Disodium  phosphate  solution  containing  10.085  grams  per  liter 

(2)  Sodium  acetate  "  "          50.000    " 

(3)  Lead  nitrate  40.000     " 

(4)  Potassium  iodid  50.000     " 
The  titrations  should  be  conducted  in  the  cold. 

147.  Water-Soluble  Phosphoric  Acid. — Glaser  has  modified 
the  volumetric  method  of  Kalmann  and  Meissels  for  the  volu- 
metric estimation  of  water-soluble  phosphoric  acid  in  superphos- 
phates so  as  to  avoid  the  double  titration  required  by  the  original 
method.24  If  methyl  orange  be  used  as  an  indicator  in  the  orig- 
inal method,  the  determination  does  not  at  once  lead  to  the  tri- 
calcium  salt,  but  the  liquid  still  contains,  after  neutralization,  some 
monocalcium  phosphate,  which  is  determined  by  a  further  titra- 
tion with  phenolphthalein  as  indicator.  In  the  modified  method 
the  total  phosphoric  acid  is  estimated  in  one  operation  as  a  tri- 
calcium  salt.  This  is  secured  by  adding,  at  the  proper  time,  an 
excess  of  calcium  chlorid.  Two  grams  of  the  superphosphate  are 
shaken  with  water  several  times  according  to  the  American  official 
method,  and  finally,  after  settling,  filtered,  and  the  insoluble  resi- 
due washed  on  the  filter  until  the  total  volume  of  the  filtrate  is  a 
quarter  of  a  liter.  Of  this,  50  cubic  centimeters  are  titrated  with 
tenth-normal  soda-lye,  with  addition  of  two  drops  of  methyl 
orange,  until  the  acid  reaction  has  entirely  disappeared.  There 
is  then  added  neutral  calcium  chlorid  solution  in  excess.  If 
iron  and  alumina  be  present,  a  slight  development  of  an  acid 
reaction  is  produced  of  which  no  account  need  be  made. 
Five  drops  of  the  phenolphthalein  solution  are  added  and 
the  titration  continued  until  the  alkaline  reaction  is  noted 
throughout  the  whole  mass.  The  alkaline  reaction  soon  dis- 
appears and  to  retain  it  several  tenths  cubic  centimeters  of 
alkali  are  necessary,  and  thus  an  excess  is  easily  used.  To  get 
very  sharp  results  it  is  advisable  to  place  the  solutions  in  a  high 
beaker,  which  is  kept  in  vigorous  rotation  until  the  alkaline  reac- 
14  Chemikcr-Zeitung,  1894,  18  :  1533. 


ESTIMATION   OF   PHOSPHORIC   ACID  167 

tion  is  first  established.  The  burette  is  quickly  read  and  a  few 
tenths  more  alkali  added  to  be  certain  that  the  unit  point  has  not 
been  missed.  On  cloudy  days  the  light  may  be  concentrated  by  a 
lens,  for  which  a  flask  filled  with  clear  water  conveniently  serves. 
Each  cubic  centimeter  of  the  soda-lye  corresponds,  in  the  first  ti- 
tration,  to  7.1  and  in  the  second  to  3.55  milligrams  of  phosphoric 
acid. 

148.  Estimation  of  Phosphoric  Acid  in  the  Presence  of  a 
Large  Excess  of  Iron. — The  volumetric  method  given  below,  due 
to  Emmerton,  depends  upon  the  precipitation  of  a  phosphomolyb- 
date,  of  constant  composition,  in  the  presence  of  a  large  excess 
of  iron,  as  in  the  analysis  of  iron  and  steel  and  iron  ores.25  The 
molybdenum  trioxid  obtained  is  reduced  by  zinc  to  Mo12O19. 
The  action  of  permanganate  on  this  compound  is  shown  in  the 
following  equation : 

5Mo12O10-f  i7(K2OMn2O7)=6oMoO3+i7K,O+34MnO. 
Seventeen  molecules  of  permanganate  are  equal  to  60  mole- 
cules of  molybdenum  trioxid.  The  iron  or  steel  is  dissolved  in 
nitric  acid,  evaporated  to  dryness,  heated,  and  redissolved  in  hy- 
drochloric acid,  then  treated  again  with  nitric  acid  and  evaporated 
until  a  clear  and  concentrated  solution  is  obtained  free  from  hy- 
drochloric acid. 

The  solution  obtained  is  diluted  to  40  cubic  centimeters  with 
water  and  washed  into  a  400  cubic  centimeter  flask,  making  the 
total  volume  about  75  cubic  centimeters.  Add  strong 
ammonia,  shaking  after  each  addition,  until  the  mass  sets  to  a 
thick  jelly  from  the  ferric  hydroxid.  Add  a  few  more  cubic 
centimeters  of  ammonia  and  shake  thoroughly,  being  sure  the 
ammonia  is  present  in  excess.  Add  next  nitric  acid  gradually, 
with  shaking,  until  the  precipitate  has  all  dissolved ;  add 
enough  more  nitric  acid  to  make  the  solution  a  clear  amber  color. 
The  volume  should  now  be  about  250  cubic  centimeters.  Bring 
the  solution  to  85°  and  add  at  once  40  cubic  centimeters  of 
molybdate  solution  of  the  following  strength  :  Dissolve  100  grams 
of  molybdic  acid  in  300  cubic  centimeters  of  strong  ammonia  and 
loo  cubic  centimeters  of  water,  and  pour  the  solution  into  1250 

25  Blair,  Chemical  Analysis  of  Iron,  Second  Edition,  1891  :  95. 


1 68  AGRICULTURAL   ANALYSIS 

cubic  centimeters  of  nitric  acid  (of  1.20  specific  gravity)  ;  close 
the  flask  with  a  rubber  stopper,  wrap  it  in  a  thick  cloth,  and  shake 
violently  for  five  minutes.  Collect  the  precipitate  on  a  filter,  using  a 
pump,  and  wash  with  dilute  nitric  acid  (iHNO3:  5oH,O).  If  a 
thin  film  of  the  precipitate  should  adhere  to  the  flask  it  can  be  re- 
moved by  the  ammonia  in  the  next  operation.  Wash  the  molyb- 
date  precipitate  into  a  500  cubic  centimeter  flask  with  dilute  am- 
monia (iH3N:4H2O),  using  about  30  cubic  centimeters.  Add 
80  cubic  centimeters  of  hot  dilute  sulfuric  acid  (iH,SO4 :4H2O) 
and  cover  the  flask  with  a  small  funnel.  Add  10  grams  of 
granulated  zinc  and  heat  until  rapid  action  begins,  and  then 
heat  gently  for  five  minutes.  The  reduction  is  then  complete. 
During  the  reduction  the  colors,  pink,  plum,  pale  green  and  dark 
green,  are  seen  in  the  molybdate  solution,  the  latter  color  mark- 
ing the  end  of  the  reaction. 

To  remove  the  zinc,  pour  through  a  large  folded  filter,  wash 
with  cold  water,  and  fill  up  the  filter  once  with  cold  water.  But 
little  oxidation  takes  place  in  this  way.  A  port  wine  color  is 
seen  on  the  filter,  but  this  does  not  indicate  a  sufficient  oxidation 
to  make  an  error. 

In  titrating,  the  color  becomes  fainter  and  finally  the  solu- 
tion is  perfectly  colorless  and  shows  a  single  drop  in  excess 
of  the  permanganate.  The  permanganate  solution,  for  conven- 
ience, is  made  so  that  one  cubic  centimeter  is  equal  to  o.oooi 
gram  of  phosphorus.  With  iron  its  value  is  one  cubic  centime- 
ter equals  0.006141  gram  of  iron;  and  one  cubic  centimeter  equals 
0.005574  gram  of  molybdenum  trioxid. 

In  the  case  of  iron  ores  10  grams  are  dissolved  in  hydrochloric 
acid,  evaporated  to  dryness,  taken  up  with  hydrochloric  acid, 
evaporated  to  a  small  bulk  and  the  residual  hydrochloric  acid  ex- 
pelled by  heating  with  nitric  acid.  The  insoluble  residue  is  re- 
moved by  filtration  and  the  rest  of  the  process  conducted  as 
above  described.  This  method  of  determination  is  advisable  in 
the  solution  of  ores  rich  in  phosphorus,  intended  for  the  manu- 
facture of  iron  or  steel  where  basic  phosphoric  slag  is  to  be  util- 
ized as  a  by-product. 

149.  Variation  of  Dudley  and  Noyes. — The    method    of    Em- 


VARIATION   OF   DUDLEY   AND   NOYES  169 

merton  for  the  determination  of  small  quantities  of  phosphoric 
acid  or  of  phosphorus  in  the  presence  of  a  large  excess  of  iron, 
has  been  modified  by  Dudley  and  Pease,26  and  by  Noyes  and 
Royse.27  As  modified,  the  method  is  not  intended  for  fertilizer 
analysis,  but  the  principle  on  which  it  rests  may  some  time,  with 
proper  modifications,  find  application  in  fertilizer  work.  The  re- 
duction is  accomplished  in  a  jones  tube,  much  simplified,  so  as 
to  render  it  suitable  for  common  use.28  The  molybdic  acid  is  re- 
duced to  a  form,  or  series  of  forms,  corresponding  to  molybdenum 
sesquioxid,  as  in  the  Emmerton  method,  and  subsequently,  as  in 
that  method,  titrated  by  a  set  solution  of  potassium  permanganate. 
The  iron  or  steel  filings,  containing  phosphorus,  are  brought 
into  solution  by  means  of  nitric  acid.  For  this  purpose  two 
grams  of  them  are  placed  in  a  half  liter  flask  together  with  50 
cubic  centimeters  of  nitric  acid  of  1.18  specific  gravity.  The 
mixture  is  boiled  for  one  minute,  and  10  cubic  centimeters  of 
permanganate  solution  of  one  and  a  quarter  per  cent,  added. 
Boil  again  until  the  pink  color  disappears.  Ferrous  sulfate  solu- 
tion is  next  to  be  carefully  added,  shaking  meanwhile,  until  the 
solution  clears.  Cool  to  50°  and  add  eight  cubic  centimeters  of 
ammonia  of  0.90  specific  gravity,  stopper  the  flask,  and  shake 
until  any  precipitate  which  may  form  is  redissolved.  Cool  or 
warm,  as  the  case  may  be,  until  the  solution  is  as  many  degrees 
above  or  below  60°  as  the  molybdic  solution  is  above  or  below 
27°.  Add  60  cubic  centimeters  of  molybdic  solution,  stopper, 
and  shake  on  a  machine  or  by  hand  for  five  minutes.  After 
remaining  at  rest  for  five  minutes  pour  into  a  nine  centimeter  fil- 
ter of  fine  texture,  and  wash  with  the  acid  ammonium  sulfate 
solution  in  quantities  of  from  five  to  10  cubic  centimeters  each 
time.  The  filtrate  and  washings  must  be  perfectly  bright.  Con- 
tinue the  washings  until  the  filtrate  gives  no  color  with  hydrogen 
sulfid. 

Dissolve    the    yellow    precipitate    with    12    cubic    centimeters 
of  0.96  ammonia  diluted  with  an  equal  volume  of  water,  and 

36  Journal  of  Analytical  and  Applied  Chemistry,  1893,  7  :  108. 
Journal  of  the  American  Chemical  Society,  1894,  16  :  224. 

77  Journal  of  the  American  Chemical  Society,  1895,  17  :  129. 

18  Blair,  Analysis  of  Iron,  Second  Edition  ,1891  :  99. 


170  AGRICULTURAL   ANALYSIS 

wash  the  filter  with  100  cubic  centimeters  of  water.  Finally  add 
to  the  filtrate  and  wash-water  80  cubic  centimeters  of  water 
and  10  of  strong  sulfuric  acid.  Pass  the  mixture  through  the 
jones  reducing  tube  and  follow  it  with  200  cubic  centimeters  of 
water,  taking  care  that  no  air  enter  the  tube  during  the  opera- 
tions. The  solution  collected  in  the  flask  should  be  at  once 
titrated  with  potassium  permanganate. 

In  cases  where  the  content  of  phosphorus  is  very  high  the  solu- 
tion of  the  yellow  precipitate  is  made  to  a  definite  volume  and 
the  reduction  and  titration  performed  on  an  aliquot  thereof. 

Solutions  Used:  (i)  Nitric  Acid. — One  part  of  nitric  acid  of 
1.42  specific  gravity  and  two  parts  of  water  by  volume.  The 
specific  gravity  of  the  mixture  is  about  1.18. 

(2)  Permanganate    Solution    for    Oxidizing. — Dissolve     12.5 
grams  of  potassium  permanganate  in  one  liter  of  water. 

(3)  Ferrous  Sulfate. — Fresh  crystals  not  effervesced  and  free 
from  phosphorus. 

(4)  Ammonia. — The  strong  ammonia    used    should    have    a 
specific  gravity  of  about  0.90  and  the  dilute  of  0.96  at  15.5°. 

(5)  Molybdic  Solution. — Dissolve  100  grams  of  molybdic  anhy- 
drid  in  400  cubic  centimeters  of  ammonia  of  0.96  specific  gravity 
and  pour  the  solution  slowly,  with  constant   stirring,  into  one 
liter  of  nitric  acid  of  about  1.20  specific  gravity.    Heat  the  mix- 
ture to  45°  and  add  one  cubic  centimeter  of  a  10  per  cent,  solu- 
tion of  sodium  phosphate,  stir  vigorously,  and  allow  to  stand  in 
a  warm  place  for  18  hours.     The  object  of  adding  the  sodium 
phosphate  is  to  remove  any  substance  which  may  contaminate  the 
yellow  precipitate.     Filter  before  using. 

(6)  Acid  Ammonium  Sulfate. — To  half  a  liter  of  water  add 
27.5  cubic  centimeters  of  0.96  ammonia  and  24  cubic  centimeters 
of  strong  sulfuric  acid,  and  make  the  volume  one  liter  with  water. 

(7)  Potassium   Permanganate   for    Titration. — Dissolve     four 
grams  of  potassium  permanganate  in  two  liters  of  water,  heat 
nearly  to  boiling   for  an   hour,   allow   to  stand   for    18   hours, 
and  filter  on  asbestos  felt.     The.  solution  must  not  come  in  con- 
tact with  rubber  or  other  organic  matter.     The  solution  may  be 
standardized  with  pure  iron  (piano  wire),  with  thoroughly  air- 


VARIATION    OF    DUDLEY    AND    NOYES 


dried  ammonium  oxalate  in  solution,  with  a  little  dilute  sulfuric 
acid  and  with  ammonium  ferrous  sulfate  partly  crystallized  in 
small  crystals  from  a  slightly  acid  solution.  The  crystals  should 
be  well  washed  and  quickly  air-dried  in  a  thin  layer.  The  factors 
-  and  -  should  be  used,  respectively,  to  calculate  the  iron  equiv- 
alent. The  phosphorus  equivalent  is  obtained  by  multiplying 
the  iron  equivalent  by  _li_  =0.0 1538. 

Reduction  Apparatus. — The  reduction  of  the  molybdic  acid  to 
molybdenum  trioxid  is  accomplished  in  a  tube  first  proposed  by 
Jones.  The  apparatus  is  shown  in  Figure  8.  A  piece  of  moder- 


Fig.  8.    Jones'  Reduction  Tube. 

ately  heavy  glass  tubing  35  centimeters  long,  with  an  internal 
diameter  of  two  centimeters,  is  drawn  out  at  the  lower  end  so  as 
to  pass  into  the  stopper  of  a  flask.  A  circular  piece  of  perforated 
platinum  or  porcelain  rests  on  the  constricted  portion  of  the  tube 
and  this  is  covered  with  an  asbestos  felt.  The  tube  is  then  nearly 
filled  with  powdered  zinc,  which  is  washed,  before  using,  with 


1 72  AGRICULTURAL   ANALYSIS 

dilute  sulfuric  acid  (i  :2o).  A,  B,  and  C  represent  different  meth- 
ods of  filtering  the  molybdic  solution.  In  A  a  platinum  cone  is 
placed  in  the  constricted  portion  of  the  tube  and  the  asbestos  felt 
placed  thereon  and  the  tube  then  filled  with  the  granulated  zinc. 
In  B  there  is  first  inserted  a  perforated  disk,  then  some  very  fine 
sand,  and  this  is  covered  with  another  disk.  In  C  there  is  a  perfor- 
ated disk  which  is  covered  with  asbestos  felt.  The  filtering  ar- 
rangement should  be"  such  as  to  prevent  any  zinc  particles  from 
reaching  the  flask  and  yet  permitting  the  filtration  to  go  on  with- 
out much  difficulty.  A  blank  determination  is  first  made  by  adding 
to  180  cubic  centimeters  of  water  12  of  0.96  ammonia  and  10  of 
strong  sulfuric  acid.  This  is  poured  through  the  reducing  tube 
and  followed  with  200  cubic  centimeters  of  water,  taking  care 
that  no  air  enter  the  apparatus.  Hydrogen  peroxid  is  formed  if 
air  enters.  Even  after  standing  for  a  few  moments  the  tube  should 
be  washed  with  dilute  sulfuric  acid  before  again  using  it.  The 
filtrate  should  be  titrated  with  the  permanganate  solution  and  the 
amount  required  deducted  from  the  following  amounts  obtained 
with  the  molybdic  salt. 

Calculations. — The  calculations  of  the  amount  of  phosphorus 
in  a  given  sample  of  iron  or  steel  are  made  according  to  the  fol- 
lowing data:29  In  a  given  case  let  it  be  supposed  that  the  per- 
manganate solution  is  set  with  a  solution  of  piano  wire  containing 
99.27  per  cent,  of  pure  iron,  and  it  is  found  that  one  cubic  centi- 
meter of  permanganate  liquor  is  equal  to  0.003466  gram  of  me- 
tallic iron.  It  is  found  that  90.76  parts  of  molybdic  acid  will  pro- 
duce the  same  effect  on  permanganate  as  100  parts  of  iron.  Hence 
one  cubic  centimeter  of  permanganate  solution  is  equivalent  to 
0.003466X0.9076=0.003145  gram  of  molybdic  acid.  In  the  yel- 
low precipitate  formed,  in  the  conditions  named  for  the  analysis 
it  is  found  that  the  phosphorus  is  one  and  nine-tenths  per  cent, 
of  the  molybdic  acid  present.  Therefore,  one  cubic  centimeter 
of  permanganate  liquor  is  equal  to  0.003145X0.019=0.0000597 
gram  of  phosphorus.  If  then,  for  example,  in  a  sample  of  iron 
or  steel  eight  and  six-tenths  cubic  centimeters  of  permanganate 

*•  Dudley  and  Pease,  Journal  of  Analytical  and  Applied  Chemistry,  1893, 
7  :  112. 


INTERNATIONAL  STEEL   STANDARDS   COMMITTEE  173 

solution,  after  correction,  be  found  necessary  to  oxidize  the  molyb- 
dic  solution  after  passing  through  the  jones  reducing  tube,  the 
amount  of  phosphorus  found  is  0.0000597X8.6=0.051  per  cent. 

150.  Methods  of  the  International  Steel  Standards  Committee.30 
— This  method  was  adopted  by  the  committee  appointed  to  con- 
sider all  the  rapid  methods  for  the  determination  of  phosphorus 
in  iron  and  steel,  and  was  recorded  as  giving  the  best  methods 
of  procedure  which  are  known  at  present  and  securing  data 
which  are  of  great  accuracy  if  the  details  of  the  process  are 
carefully  observed.  The  process  is  conducted  as  follows: 

From  one  to  two  grams  of  the  drillings  of  iron  or  steel,  accord- 
ing to  the  phosphorus  which  they  contain,  are  placed  in  a  250 
cubic  centimeter  erlenmeyer  flask  and  covered  with  100  cubic 
centimeters  of  nitric  acid  of  1.135  specific  gravity.  The  flask  is 
covered  with  a  watch-glass  and  the  mixture  is  heated  until  the 
solution  is  complete  and  the  nitric  acid  is  boiled  off.  Ten  cubic 
centimeters  of  strong  potassium  permanganate  solution  are  added 
and  boiling  continued  until  the  pink  color  has  disappeared  and 
the  manganese  dioxid  has  separated.  Afterwards  a  few  drops 
of  the  solution  of  sulfurous  acid  are  added  and  a  small  crystal  of 
ferrous  sulfate,  or  a  solution  of  0.5  gram  of  sodium  hyposulfite 
in  10  cubic  centimeters  of  water.  The  addition  of  these  reagents 
is  continued  at  short  intervals  until  the  precipitated  manganese 
dioxid  is  dissolved.  After  boiling  for  two  minutes  the  flask  is 
placed  in  cool  water  or  allowed  to  stand  until  it  is  cool,  and 
then  40  cubic  centimeters  of  dilute  ammonia  of  0.96  specific 
gravity  are  added.  The  precipitated  ferric  hydrate  will  redis- 
solve  when  the  liquid  is  thoroughly  mixed.  After  cooling  to 
about  room  temperature  the  flask  is  stoppered  and  shaken  for 
five  minutes,  either  by  hand  or  in  a  shaking  machine.  After 
standing  for  a  few  minutes,  the  contents  of  the  flask  are  poured 
on  a  filter  and  washed  with  acid  ammonium  sulfate,  prepared 
by  adding  1 5  cubic  centimeters  of  strong  ammonia  to  one  liter  of 
water  and  25  cubic  centimeters  of  strong  sulfuric  acid,  until 
two  or  three  cubic  centimeters  of  the  wash-water  give  no  reac- 
tion for  molybdenum  with  a  drop  of  ammonium  sulfid.  Any 
30  Blair,  The  Chemical  Analysis  of  Iron,  6th  Edition ,  1906  :  92. 


174  AGRICULTURAL   ANALYSIS 

adhering  ammonium  phosphomolybdate  is  dissolved  with  ammo- 
nia and  added  to  the  precipitate  in  the  filter,  and  the  filtrate  is 
collected  in  a  250  cubic  centimeter  griffin  beaker.  The  flask  is 
washed  with  water  which  is  poured  upon  the  filter  and  the  filter 
is  thoroughly  washed  until  the  solution  measures  about  60  cubic 
centimeters.  To  this  are  added  10  cubic  centimeters  of  strong 
sulfuric  acid  and  the  solution  is  passed  through  the  reductor, 
similar  in  construction  to  the  jones  reductor  already  described. 
Care  should  be  exercised  to  keep  the  end  of  the  small  tube  of  the 
reductor  just  below  the  surface  of  the  liquid  in  the  flask.  The 
heat  which  is  caused  by  mixing  the  strong  sulfuric  acid  with 
the  ammoniacal  solution  immediately  before  passing  it  through 
the  reductor  is  sufficient  to  insure  a  complete  reduction.  The 
other  precautions  which  have  already  been  described  to  prevent 
the  access  of  air  should  be  observed,  and  the  operations  should 
be  so  continued  that  the  whole  reduction  occupies  about  three 
or  four  minutes.  The  liquid  as  it  passes  through  the  reductor 
should  be  bright  green  in  color.  Permanganate  solution  is  added 
and  the  green  color  disappears.  The  solution  becomes  first, 
brown,  then  pinkish  yellow,  and  ultimately  colorless.  The  ad- 
dition of  permanganate  is  continued  drop  by  drop  until  the  solu- 
tion assumes  a  faint  pink  coloration,  which  remains  at  least  one 
minute.  From  the  reading  of  the  burette  the  amount  of  per- 
manganate consumed  in  the  blank  determination,  obtained  as 
described  under  the  method  for  standardizing  permanganate 
solution,  is  subtracted  and  the  number  of  cubic  centimeters  thus 
obtained  is  multiplied  by  the  value  of  one  cubic  centimeter  in 
terms  of  phosphorus.  This  product  is  multiplied  by  100  and  di 
vided  by  the  weight  of  the  sample  used  and  the  resulting  quotient 
is  the  percentage  of  phosphorus  in  the  steel. 

151.  Standardization  of  the  Solution  of  Potassium  Permangan- 
ate.— This  solution  is  prepared  by  dissolving  two  grams  of  crys- 
tallized potassium  permanganate  in  one  liter  of  distilled  water 
and  filtering  through  asbestos.  For  determining  its  value  from 
0.15  to  0.25  gram  of  clean  soft  steel  wire,  in  which  the  content 
of  iron  has  been  carefully  determined,  is  put  in  an  erlenmeyer 
flask  of  125  cubic  centimeters  capacity  and  covered  with  30  cubic 


OPERATION  OF  THE  REDUCTOR 


175 


centimeters  of  distilled  water  and  10  of  strong  sulfuric  acid. 
The  flask  is  covered  with  a  watch-glass  and  heated  until  the  solu- 
tion of  the  wire  is  complete.  A  sufficient  amount  of  the  strong 
solution  of  potassium  permanganate  is  added  to  oxidize  the  iron 
and  destroy  the  carbonaceous  matter,  avoiding  however  any  ex- 


Fig.  9.    Reductor  and  Filter  Attachment.  Fig.  10.    Permanganate  Burette. 

(Courtesy  of  A.  H.  Blair  and  J.  B.  Lippincott  Co.) 

cess  which  would  cause  a  precipitate  of  manganese  dioxid.  If 
any  precipitate  is  formed  it  is  redissolved  by  adding  a  very  few 
drops  of  sulfurous  acid  and  boiling  until  every  trace  is  removed. 
After  cooling  10  cubic  centimeters  of  dilute  ammonia  are  added 
and  the  solution  passed  through  a  jones  reductor. 

152.  Operation  of  the  Reductor. — Everything  in  connection 
with  the  reductor  should  be  clean  and  proved  to  be  in  good  order 
by  previous  treatment  with  dilute  sulfuric  acid  and  washing  with 


176  AGRICULTURAL  ANALYSIS 

distilled  water.  To  this  end  the  flask  should  be  attached  to  the 
filter  pump  as  shown  in  the  figure.  One  hundred  cubic  centi- 
meters of  warm  dilute  sulfuric  acid  are  placed  in  the  funnel  b,  and 
the  stop-cock  c  opened.  When  the  funnel  is  almost  empty,  the 
solution  which  is  to  be  reduced  is  transferred  thereto.  The  solu- 
tion should  be  hot,  but  not  boiling.  The  vessel  which  held  the 
solution  should  be  washed  with  dilute  sulfuric  acid,  and  this 
added  to  the  funnel  again  when  it  is  nearly  empty  in  such  a  way 
as  to  wash  it  thoroughly  and  this  should  be  followed  with  about 
200  cubic  centimeters  more  of  warm  dilute  sulfuric  acid,  and  50 
cubic  centimeters  of  hot  distilled  water.  In  no.  case  is  the  funnel 
allowed  to  become  empty,  and  the  stop-cock  c  is  closed  when 
there  is  still  a  little  of  the  wash-water  left  in  the  funnel  above 
fhe  surface  of  the  zinc.  In  this  way  air  is  prevented  from  pass- 
ing into  the  reductor  tube.  Blank  determination  is  made  by 
passing  through  the  reductor  a  mixture  containing  10  cubic 
centimeters  of  strong  phosphoric  acid,  10  cubic  centimeters  of 
dilute  ammonia,  and  50  cubic  centimeters  of  water.  This  is 
preceded  and  followed  by  the  dilute  acid  as  described  above 
The  amount  of  potassium  permanganate  required  to  give  this 
blank  a  distinct  color  is  subtracted  from  the  amount  required 
to  give  the*  same  color  to  each  reduced  solution.  To  estimate 
the  value  of  the  solution  the  weight  of  the  iron  wire  used  is 
multiplied  by  the  percentage  of  the  iron  in  the  wire  and  divided 
by  the  number  of  cubic  centimeters  of  potassium  permanganate 
in  terms  of  metallic  iron.  The  result  is  multiplied  by  the  factor 
0.88163  which  is  the  ratio  of  molybdic  acid  to  iron,  and  this 
product  by  0.01794  which  is  the  ratio  of  phosphorus  to  molybdic 
acid,  and  the  result  is  the  value  of  one  cubic  centimeter  of  the 
permanganate  solution  in  terms  of  phosphorus.  The  formula 
of  the  reduced  molybdic  acid  is  given  as  Mo24O37. 

153.  Calculating  Results. — To  illustrate  the  method  of  calcu- 
lating results  Blair  gives  the  following  example:  The  weight 
of  the  wire  represented  by  0.1745  gram  requires  50  cubic  centi- 
meters of  permanganate  to  give  the  required  color.  A  blank 
determination  carried  on  as  described  above  shows  o.i  cubic 
centimeter  of  permanganate,  so  the  quantity  required  by  the 


THE   SILVER   METHOD  177 

wire  is  49.9  cubic  centimeters  permanganate.  The  wire  con- 
tains 99.87  per  cent,  of  iron.  We  have  then  the  following 
equation;  namely,  0.1745X0.9987-^-49.9=0.0034923.  This  shows 
that  one  cubic  centimeter  of  permanganate  is  equivalent  to  that 
quantity  expressed  as  0.0034923  gram  metallic  iron.  Multiply- 
ing the  value  in  iron  by  the  ratio  of  molybdic  acid  to  iron, 
namely,  0.88163,  and  the  product  by  the  ratio  of  phosphorus  to 
molybdic  acid,  namely,  0.01794,  the  product  is  found  to  be 
0.000055238.  This  indicates  that  one  cubic  centimeter  of  per- 
manganate is  equivalent  to  0.000055238  gram  of  phosphorus.  If 
the  precipitated  ammonium  phosphomolybdate  from  two  grams 
of  steel  require  35.5  corrected  cubic  centimeters,  then  the  per- 
centage of  phosphorus  in  steel  is  obtained  by  the  following  for- 
mula: 35.5Xo.oooo55238Xioo-:-2=:o.098,  which  is  equivalent 
to  the  percentage  of  the  phosphorus  of  the  steel.  For  further 
details  of  the  process  the  work  of  Blair,  already  cited,  should 
be  consulted. 

154.  The  Silver  Method. — The  separation  of  the  phosphoric 
acid  by  silver  according  to  the  method  of  Perrot  has  been  inves- 
tigated by  Spencer,  who  found  the  process  unreliable.31  By  a 
modification  of  the  process,  however,  Spencer  obtained  fairly  sat- 
isfactory results.  The  principle  of  this  method  depends  on  the 
separation  of  the  phosphoric  acid  by  silver  carbonate  and  the  sub- 
sequent titration  thereof  with  standard  uranium  solution  after 
the  removal  of  the  excess  of  silver.  The  operation  is  conducted 
as  follows :  The  fertilizer  is  first  ignited  until  all  organic  matter 
and  residual  carbon  are  destroyed.  Solution  is  then  accomplished 
by  .means  of  nitric  acid  and  the  volume  completed  to  a  definite 
quantity.  To  an  aliquot  part  of  the  slightly  acid  (nitric)  solu- 
tion, after  filtration,  varying  with  the  supposed  strength  of  the 
solution  so  as  to  contain  about  100  milligrams  of  phosphorus 
pentoxid,  freshly  prepared  silver  carbonate  is  added  in  excess, 
that  is,  sufficient  to  saturate  any  free  acid  present  and  also  to 
combine  with  all  the  phosphoric  acid.  Wash  thoroughly  with 
hot  water  and  then  dissolve  the  mixed  phosphate  and  silver  car- 
bonate in  nitric  acid,  and  remove  the  silver  from  the  solution  with 
31  Eighth  Annual  Report  of  Purdue  University,  1882  :  240. 


178  AGRICULTURAL   ANALYSIS 

sodium  chlorid.  The  phosphoric  acid  is  determined  in  the  filtrate 
by  means  of  a  standard  solution  of  uranium  nitrate  in  the  man- 
ner already  described.  Spencer  found  that  the  separation  of 
the  phosphoric  acid  by  the  silver  method  was  more  exact  than  by 
the  Joulie  magnesium  citrate  process.  With  practice  on  the  part 
of  the  analyst  in  determining  the  end  reaction,  the  process  is  both 
rapid  and  accurate.  The  method  is  also  inexpensive,  as  both  the 
silver  and  uranium  are  easily  recovered  from  the  waste. 

155.  Volumetric  Silver  Method. — Holleman  has  proposed  a 
modification  of  the  silver  method  for  the  volumetric  determina- 
tion of  phosphoric  acid,  having  for  its  chief  purpose  the  more  ac- 
curate and  easy  determination  of  the  end  reaction,  which  is  con- 
ducted as  described  below.32  The  reaction  which  takes  place  is 
represented  by  the  equation,  Na2HPO4-f3AgNO3=:Ag3PO4-|- 
2NaNO3-(-HNO3.  Although  silver  phosphate  is  insoluble  in 
water,  the  nitric  acid  formed  holds  some  of  it  in  solution.  To 
prevent  this,  acetate  of  soda  is  added  in  excess,  and  thus  the  whole 
of  the  phosphoric  acid  is  obtained  as  a  silver  salt.  The  light  is 
to  be  excluded  during  the  determination  by  wrapping  the  flask  in 
a  black  cloth  to  avoid  a  discoloration  of  the  silver  compound. 
Yolhard's  reaction  for  silver  is  based  on  the  fact  that  when  solu- 
tions of  silver  and  an  alkaline  thiocyanate  are  mixed  in  the  pres- 
ence of  a  ferric  salt,  silver  is  precipitated  as  thiocyanate.33  As  soon 
as  the  least  excess  of  thiocyanate  is  added,  brown  ferric  thio- 
cyanate is  formed,  and  this  marks  the  end  point  of  the  solution. 

In  a  flask  of  200  cubic  centimeters  capacity  are  placed  50  cubic 
centimeters  of  the  liquid  to  be  analyzed,  which  should  not  contain 
more  than  two-tenths  gram  of  phosphoric  acid.  The  solution  is 
treated  with  10  cubic  centimeters  of  a  normal  solution  of  sodium 
acetate  and  afterwards  with  a  slight  excess  of  decinormal  silver 
solution,  four  and  five-tenths  cubic  centimeters  for  each  o.oi 
gram  of  phosphoric  acid.  The  solution  is  neutralized  with  tenth- 
normal  sodium  hydroxid,  the  amount  required  having  been  pre- 
viously determined  by  titrating  10  cubic  centimeters  of  the  liquid 
to  be  analyzed,  using  phenolphthalein  as  an  indicator.  Five  times 

"  Recueil  des  Travaux  chimiques  des  Pays-Bas,  1893,  12  :  I. 

M  Liebig's  Annalen  der  Chemie,  1877,  190  :  I. 


DESIRABILITY   OF    METHODS  179 

the  quantity  required  for  the  neutralization  of  the  10  cubic  centi- 
meters is  added,  less  one-half  cubic  centimeter.  By  this  treatment 
the  phosphoric  acid  in  the  presence  of  sodium  acetate  is  completely 
precipitated  as  silver  phosphate.  The  excess  of  silver  is  determined 
by  diluting  the  mixture  to  200  cubic  centimeters,  filtering,  and 
titrating  100  cubic  centimeters  of  the  filtrate  with  ammonium  thio- 
cyanate,  using  a  ferric  salt  (ferric-potassium-alum)  as  indicator. 
The  presence  of  sulfuric  and  nitric  acids  does  not  interfere  with 
the  reaction,  but,  of  course,  hydrochloric  acid  must  be  absent. 
Alkalies  and  alkaline  earth  metals  may  be  present,  but  not  the 
heavy  metals. 

When  iron  and  aluminum  are  present  100  cubic  centimeters  of 
the  solution  are  precipitated  with  30  cubic  centimeters  of  nor- 
mal sodium  acetate,  the  phosphoric  acid  is  determined  in  50  cubic 
centimeters  of  the  filtrate,  and  the  precipitate  of  iron  and  alumi- 
num phosphates  is  ignited  and  weighed,  and  its  weight  multiplied 
by  2.225  is  added  to  the  phosphoric  anhydrid  found  volumetric- 
ally.  If  ammonia  be  present  it  must  be  removed  by  boiling,  as 
otherwise  it  affects  the  titration  with  phenolphthalein. 

For  agricultural  purposes  this  method  can  have  but  little  value, 
inasmuch  as  the  phosphates  to  be  examined  almost  always  have 
a  certain  proportion  of  iron  and  aluminum.  Moreover,  since  the 
amount  of  these  bases  has  to  be  determined  gravimetrically,  there 
would  be  no  gain  in  time  and  no  simplification  of  the  processes 
by  the  use  of  the  volumetric  method  as  proposed. 

TECHNICAL  DETERMINATION  OF  PHOSPHORIC  ACID 

156.  Desirability  of  Methods. — In  the  preceding  paragraphs,  has 
been  given  a  statement  of  the  principal  methods  now  in  use  by 
chemists  and  others  connected  with  fertilizer  control  for  the 
scientific  and  agronomic  determinations  of  phosphoric  acid,  and 
its  agricultural  value. 

A  resume  of  the  important  methods,  in  a  form  suited  to  use 
in  a  factory  for  preparing  phosphatic  fertilizers  for  the  market, 
seems  desirable.  In  these  factories  the  chemists  have  been  accus- 
tomed to  use  their  own,  or  private  methods,  and  there  has  not 
been  a  general  disposition  among  them  to  publish  their  methods 
and  experience  for  the  common  benefit.  For  factory  processes, 


l8o  AGRICULTURAL   ANALYSIS 

a  method  should  be  not  only  reasonably  accurate,  but  also  simple 
and  rapid.  It  is  evident,  therefore,  that  the  general  principles 
already  indicated  must  underlie  any  method  which  would  prove 
useful  in  factory  work.  The  final  determination  by  the  technical 
chemist  for  the  purpose  of  labeling  and  complying  with  the  laws 
of  the  various  States,  should  in  all  cases  be  conducted  by  the 
official  methods.  Albert  has  made  a  resume  of  methods  applica- 
ble for  factory  control,  and  these  are  given  here  for  convenience, 
although  they  are,  in  many  respects,  but  condensed  statements 
of  methods  already  described.34 

157.  Reagents.  Molybdate  Solution. — One  hundred  and  ten 
grams  of  pure  molybdic  acid  are  dissolved  in  ammonia  of  nine- 
tenths  specific  gravity  and  diluted  with  water  to  one  liter.  The 
solution  is  poured  into  one  liter  of  nitric  acid,  of  one  and  two- 
tenths  specific  gravity,  and,  after  standing  a  few  days,  filtered. 

Concentrated  Ammonium  Nitrate  Solution. — Seven  hundred 
and  fifty  grams  of  pure  ammonium  nitrate  are  dissolved  in  water 
and  made  up  to  one  liter. 

Magnesia  Mixture. — Fifty-five  grams  of  magnesium  chlorid, 
70  grams  of  ammonium  chlorid  and  130  cubic  centimeters  of  am- 
monia of  nine-tenths  specific  gravity  are  dissolved  and  diluted  with 
water  to  one  liter. 

Two  and  One-Half  Per  Cent.  Ammonia. — One  hundred  cubic 
centimeters  of  ammonia  of  nine-tenths  specific  gravity  are  diluted 
with  water  to  one  liter. 

Joulie's  Citrate  Solution. — Four  hundred  grams  of  citric  acid 
are  dissolved  in  ammonia  of  nine-tenths  specific  gravity  and  di- 
luted to  one  liter  with  ammonia  of  the  same  strength. 

Wagner's  Citrate  Solution. — One  hundred  and  fifty  grams  of 
citric  acid  are  exactly  neutralized  with  ammonia,  then  10  grams 
of  citric  acid  added  and  diluted  to  one  liter  with  water. 

Sodium  Acetate  Solution. — One  hundred  grams  of  crystallized 
sodium  acetate'  are  dissolved  in  water,  treated  with  100  cubic 
centimeters  of  acetic  acid,  and  diluted  to  one  liter  with  water. 

Calcium  Phosphate  Solution. — About  10  grams  of  dry,  pure 
tribasic  calcium  phosphate  are  dissolved  in  nitric  acid  and  dilu- 
34  Zeitschrift  fur  angewandte  Chemie,  1891,  4  :  278. 


REAGENTS  l8l 

ted  with  water  to  one  liter.  In  this  solution  the  phosphoric  acid 
is  determined  gravimetrically  by  the  molybdate  or  citrate  method, 
and  the  value  of  the  solution  marked  on  the  flask  containing  it. 

Titrated  Uranium  Solution. — Two  hundred  and  fifty  grams  of 
uranium  nitrate  are  dissolved  in  water,  25  grams  of  sodium  ace- 
tate added,  and  the  whole  diluted  to  seven  liters.  One  cubic 
centimeter  of  this  solution  corresponds  to  about  0.005  gram  of 
phosphorus  pentoxid.  In  order  to  determine  its  exact  value  pro- 
ceed as  follows.  Twenty-five  cubic  centimeters  of  the  calcium 
phosphate  solution  which,  for  example,  has  been  found  to  contain 
0.10317  gram  of  phosphorus  pentoxid,  are  neutralized  in  a  por- 
celain dish  with  ammonia,  acidified  with  acetic,  treated  with  10 
cubic  centimeters  of  sodium  acetate  solution  and  warmed.  Through 
a  burette  as  much  uranium  solution  is  allowed  to  flow  as  is  neces- 
sary to  show  in  a  drop  of  the  solution  taken  out  of  the  dish,  when 
treated  with  a  drop  of  pure  potassium  ferrocyanid,  a  slight  brown 
color.  In  order  to  be  certain,  this  operation  is  repeated  two  or 
three  times  with  new  quantities  of  25  cubic  centimeters  of  calcium 
phosphate  solution.  Example : 

Twenty-five  cubic  centimeters  of  the  calcium  phosphate  solu- 
tion containing  0.10317  gram  of  phosphorus  pentoxid,  gave  as  a 
mean  of  three  determinations  23.2  cubic  centimeters  of  the  ura- 
nium solution  necessary  to  produce  the  brown  color  with  potas- 

o  10^17 
sium  ferrocyanid.     Consequently  — '- —      -  =   0.00445    gram   of 

phosphorus  pentoxid  equivalent  to  one  cubic  centimeter  of  ura- 
nium solution.  If,  for  instance,  a  quantity  of  fertilizer  weighing 
exactly  five  grams,  requires  10  cubic  centimeters  of  the  uranium 
solution  for  the  complete  precipitation  of  its  phosphoric  acid, 
then  the  quantity  of  phosphoric  acid  contained  in  the  fertilizer 
would  be  equivalent  to  10X0.00445,  equivalent  to  0.0445  gram  of 
phosphorus  pentoxid.  The  fertilizer,  therefore,  contains  0.89  per 
cent,  of  phosphorus  pentoxid. 

Conduct  of  the  Molybdate  Method. — This  method  rests  upon 
the  precipitation  of  the  phosphorus  pentoxid  by  a  solution  of 
ammonium  molybdate  in  nitric  acid,  solution  of  the  precipitate 
in  ammonia,  and  subsequent  precipitation  with  magnesia. 


l82  AGRICULTURAL  ANALYSIS 

Manipulation. — Twenty-five  or  50  cubic  centimeters  of  a  solu- 
tion of  the  phosphate  which  has  been  made  up  to  a  standard  vol- 
ume and  contains  about  one-tenth  gram  of  phosphorus  pent- 
oxid,  are  placed  in  a  beaker  together  with  100  cubic  centimeters 
of  the  molybdate  solution  and  treated  with  as  much  ammonium 
nitrate  solution  as  will  be  sufficient  to  give  the  liquid  a  content 
of  15  per  cent,  of  ammonium  nitrate.  The  contents  of  the  beaker 
are  well  mixed  and  warmed  for  about  20  minutes  at  from  60°  to 
80. °  After  cooling,  they  are  filtered  and  the  precipitate  washed 
on  the  filter  with  cold  water  until  a  drop  of  the  filtrate  saturated 
with  ammonia  does  not  become  opaque  on  treatment  with  am- 
monium oxalate.  The  filtrate  is  washed  from  the  filter  with  2.5 
per  cent,  ammonia  solution  and  precipitated  slowly  and  with  con- 
stant stirring  by  the  magnesia  mixture.  After  standing  for  two 
hours  the  ammonium  magnesium  phosphate  is  separated  by  filtra- 
tion, washed  with  2.5  per  cent,  ammonia  until  the  filtrate  contains 
no  more  chlorin,  and  ignited. 

Conduct  of  the  Citrate  Method. — The  principle  of  this  method 
depends  upon  the  fact  that  when  a  sufficient  quantity  of  ammo- 
nium citrate  is  added  to  phosphate  solutions,  iron,  alumina,  and 
lime  are  retained  in  solution  when,  on  the  addition  of  the  mag- 
nesia mixture  in  the  presence  of  free  ammonia,  the  phosphoric 
acid  is  completely  precipitated  as  ammonium  magnesium  phos- 
phate. 

Manipulation. — From  10  to  50  cubic  centimeters  of  the  solu- 
tion of  the  phosphate  to  be  determined  are  treated  with  15 
cubic  centimeters  of  the  Joulie  citrate  solution  avoiding  warm- 
ing. A  few  pieces  of  filter  paper,  the  ash  content  of  which  is 
known,  are  thrown  in  and,  with  stirring,  15  cubic  centimeters 
of  magnesia  mixture  slowly  added  and  if  necessary  also  some  free 
ammonia.  By  the  small  pieces  of  filter  paper  the  collection  of 
the  precipitate  against  the  sides  of  the  vessel  and  on  the  stirring 
rod  is  prevented  and  in  this  way  the  production  of  the  precipitate 
hastened.  After  standing  from  one-half  an  hour  to  two  hours  the 
mixture  is  filtered,  ignited,  and  weighed.  If  it  be  preferred  to 
estimate  the  phosphoric  acid  by  titration,  the  precipitate  is  dis- 
solved in  a  little  nitric  acid  made  slightly  alkaline  with  ammonia, 


REAGENTS  183 

and  then  acid  with  acetic  and  then  afterwards  titrated  with  the 
standard  uranium  solution. 

Conduct  of  the  Uranium  Method. — The  principle  upon  which 
this  method  rests  depends  upon  the  fact,  that  uranium  nitrate  or 
acetate  precipitates  uranium  phosphate  from  solutions  contain- 
ing phosphoric  acid  and  which  contain  no  other  free  acid  except 
acetic.  In  the  presence  of  ammonium  salts  the  precipitate  is 
uranium  ammonium  phosphate  having  the  formula  PO4NH4UrO2. 
The  smallest  excess  of  soluble  uranium  salt  is  at  once  detected 
by  the  ordinary  treatment  with  potassium  ferrocyanid. 

Manipulation. — In  all  cases  the  solution  is  first  made  slightly 
alkaline  with  ammonia  and  then  acid  by  a  few  drops  of  acetic 
so  that  no  free  mineral  acid  may  be  present. 

1 i )  With  liquids  free  of  iron  : 

If,  on  the  addition  of  ammonium  or  sodium  acetate,  no  tur- 
bidity be  produced,  the  liquid  is  free  of  iron  and  alumina.  In 
this  case  from  10  to  50  cubic  centimeters  of  the  solution  con- 
taining about  one-tenth  gram  of  phosphorus  pentoxid  are  treated 
with  10  cubic  centimeters  of  sodium  acetate,  and  afterwards 
with  a  quantity  of  uranium  solution  corresponding,  as  nearly  as 
possible,  to  its  supposed  content  of  phosphorus  pentoxid,  and 
heated  to  boiling.  From  the  heated  liquid,  by  means  of  a  glass 
rod,  one  or  two  drops  are  taken  and  placed  upon  a  porcelain 
plate  and  one  drop  of  a  freshly  prepared  solution  of  potassium 
ferrocyanid  allowed  to  flow  on  it.  If  no  brown  color  be  seen  at 
the  point  of  contact  of  the  two  drops,  additional  quantities  of  the 
uranium  solution  are  added  and,  after  boiling,  again  tested  with 
potassium  ferrocyanid  until  a  brown  color  is  distinctly  visible. 
The  quantity  of  the  uranium  solution  thus  having  been  deter- 
mined, duplicate  analyses  can  be  made  and  the  whole  quantity 
of  the  uranium  solution  added  at  once  with  the  exception  of  the 
last  drops  which  are  added  as  before. 

(2)  Solutions  containing  iron  and  alumina. 

The  solution  is  treated  with  the  ammonium  citrate  solution  of 
Joulie,  the  magnesia  mixture  added  slowly,  and  the  precipitate 
collected  on  a  filter  and  washed  with  2.5  per  cent,  ammonia.  The 
precipitate  is  then  dissolved  in  nitric  acid,  made  alkaline  with 


184  AGRICULTURAL  ANALYSIS 

ammonia,  and  then  acid  with  acetic.  This  solution  is  treated 
with  10  cubic  centimeters  of  sodium  acetate  and  titrated  with 
uranium,  as  described  in  ( i ) .  As  an  alternative  method,  200  cubic 
centimeters  of  the  superphosphate  solution  may  be  treated  with  50 
cubic  centimeters  of  sodium  acetate,  allowed  to  stand  for  some 
time,  and  filtered  through  a  filter  of  known  ash  content.  In  50 
cubic  centimeters  of  the  filtrate,  which  correspond  to  40  cubic 
centimeters  of  the  original  solution,  phosphoric  acid  may  be  de- 
termined as  described  above.  The  precipitate,  consisting  of  iron 
and  aluminum  phosphates,  is  washed  three  times  on  the  filter  with 
boiling  water,  dried,  and  ignited  in  a  platinum  dish.  The  weight 
of  ignited  precipitate,  diminished  by  the  weight  of  the  ash  con- 
tained in  the  filter  and  divided  by  two,  gives  the  quantity  of  phos- 
phorus pentoxid  which  it  is  necessary  to  add  to  that  obtained  by 
titration. 

158.  Determination  of  the  Phosphoric  Acid  in  all  Phosphates 
and  Basic  Slags. 

(i)   Total  Phosphoric  Acid: 

Five  grams  of  the  fine  phosphate  meal,  or  slag  meal,  are  moist- 
ened in  a  flask  of  500  cubic  centimeters  content  with  some  water 
and  boiled  on  a  sand  bath  with  40  cubic  centimeters  of  hydro- 
chloric acid  of  from  16°  to  20°  Beaume.  The  boiling  is  continued 
until  only  a  few  cubic  centimeters  of  a  thick  jelly  of  silicic  acid 
remain.  After  cooling,  some  water  is  added  and  the  phosphate 
shaken  until  the  thick  lumps  of  silica  are  finely  divided.  The 
flask  is  then  filled  to  500  cubic  centimeters  and  its  contents  fil- 
tered. Fifty  cubic  centimeters  of  the  filtrate  are  mixed  with  15 
cubic  centimeters  of  the  Joulie  solution  and  treated  in  the  manner 
described  with  magnesia  mixture,  precipitated,  ignited  and 
weighed.  The  precipitate  can  also  be  dissolved  and  treated  with 
uranium  solution  as  described. 

The  method  used  by  Oliveri  for  basic  slags  may  also  be  em- 
ployed and  it  is  carried  out  as  indicated  in  the  following  descrip- 
tion.SB 

A  weighed  quantity  of  the  slag  is  reduced  to  a  fine  powder. 
To  five  grams  of  the  sample  is  added  three  times  its  weight  of 
34  Le  Stazioni  sperimentali  agrarie  italiane,  1891,  20  :  159. 


PHOSPHATES    AND     BASIC     SLAGS  185 

potassium  chlorate  and  the  whole  is  intimately  mixed.  The  mix- 
ture is  then  placed  in  a  porcelain  dish  and  hydrochloric  acid 
is  added,  little  by  little,  until  the  potash  salt  is  completely  decom- 
posed. It  is  evaporated  until  the  mass  is  dry.  The  material  is 
then  treated  with  fuming  nitric  acid,  and  the  determination  of 
the  phosphorus  is  made  by  the  ordinary  gravimetric  method. 

By  carrying  on  the  operation  as  described  above,  a  reduction 
of  phosphoric  acid  is  avoided,  and  the  presence  of  an  abundant 
quantity  of  potash  prevents  the  formation  of  basic  iron  phosphate 
which  is  insoluble  in  nitric  acid. 

(2)  Citrate-Soluble  Phosphoric  Acid. — One  gram  of  the  basic 
slag  or  phosphate  is  placed  in  a  100  cubic  centimeter  flask  and 
covered  with  Wagner's  acid  citrate  solution  making  the  total  vol- 
ume up  to  100  cubic  centimeters.  With  frequent  shaking  the 
flask  is  kept  at  40°  for  an  hour,  or  it  may  be  allowed  to  stand  for 
12  hours  at  room  temperature  with  frequent  shaking.  In  50 
cubic  centimeters  of  the  filtrate  from  this  flask  the  phosphoric 
acid  is  determined  by  the  magnesia  mixture  as  described.  Since, 
in  the  present  case,  the  precipitate  of  ammonium  magnesium 
phosphate  contains  some  silicic  acid  it  can  not  be  directly  ignited 
but  must  be  treated  in  the  following  manner:  The  precipitate 
and  the  filter  are  thrown  into  a  porcelain  dish,  the  filter  paper 
torn  up  into  shreds  with  a  glass  rod,  the  precipitate  dissolved 
in  nitric  acid,  neutralized  with  ammonia,  acidified  with  acetic, 
and  treated  with  uranium  solution.  The  phosphoric  acid  may 
also  be  estimated  by  the  gravimetric  method  by  dissolving  the 
precipitate  again  in  hydrochloric  or  nitric  acid,  evaporating  to 
dry  ness,  and  drying  for  one  hour  at  from  110°  to  120°,  dissolv- 
ing again  in  hydrochloric  acid,  filtering,  and  washing  the  precip- 
itate well.  The  filtrate,  which  is  now  free  from  silica,  can  be 
treated  with  Joulie's  solution,  precipitated  with  magnesia  mixture, 
the  precipitate  washed,  ignited,  and  weighed  as  described.  The 
molybdate  method  is  preferred  in  the  estimation  of  citrate-solu- 
ble phosphoric  acid,  especially  in  slags.  For  this  purpose  50  cubic 
centimeters  of  the  filtrate  from  the  solution  of  one  gram  of  slag 
in  100  cubic  centimeters  of  Wagner's  citrate  liquid  are  treated 
with  100  cubic  centimeters  of  molybdenum  solution  and  30  cubic 


1 86  AGRICULTURAL  ANALYSIS 

centimeters  of  ammonium  nitrate  solution,  warmed  for  20  minutes 
at  80°,  filtered  after  cooling,  and  the  yellow  precipitate  washed 
with  cold  water.  The  water  will  gradually  dissolve  all  the  silicic 
acid  from  the  yellow  precipitate  and  carry  it  into  the  filtrate.  The 
yellow  precipitate  is  then  dissolved  in  2.5  per  cent,  liquid  ammonia 
and  precipitated  with  magnesia  mixture  and  the  precipitate 
washed,  ignited  and  weighed  in  the  way  described. 

159.  Determination  of  Phosphoric  Acid  in  Superphosphates. 
—  (i)  Citrate-Soluble  Phosphoric  Acid. — Five  grams  of  the  su- 
perphosphate are  rubbed  with  100  cubic  centimeters  of  Wagner's 
acid  citrate  solution  in  a  mortar  and  washed  into  a  flask  of  500 
cubic  centimeters  content  and  .diluted  to  500  cubic  centimeters 
with  water.  With  frequent  shaking,  the  flask  is  allowed  to 
stand  for  12  hours,  after  which  its  contents  are  filtered.  Fifty 
cubic  centimeters  of  the  filtrate  are  treated  with  10  cubic  centi- 
meters of  the  Joulie  solution  and  15  cubic  centimeters  of  the  mag- 
nesia mixture  and,  if  necessary,  made  distinctly  alkaline  with  am- 
monia, vigorously  stirred,  and,  after  two  hours,  filtered.  The 
precipitate  is  washed,  ignited,  and  weighed  as  described,  or  titrat- 
ed, after  solution  in  nitric  acid  and  the  addition  of  sodium  ace- 
tate, with  uranium  solution.  Example:  The  weighed  precipi- 
tate has  0.1272  gram  Mg2P2O7,  then  the  phosphate  contains 
12.72X2X0.64=16.28  per  cent,  of  citrate-soluble  P2O5. 

(2)  Water-Solitble  Phosphoric  Acid. — Twenty  grams  of  super- 
phosphate are  rubbed  in  a  mortar  and  washed  into  a  flask  of  one 
liter  content  and  made  up  to  the  mark  with  water.  After  two 
hours  digestion  with  frequent  shaking,  the  contents  of  the  flask 
are  filtered  through  a  folded  filter.  Twenty-five  cubic  centime- 
ters of  the  filtrate  equivalent  to  0.5  gram  of  the  substance  are 
precipitated  with  magnesia  mixture,  the  precipitate  filtered, 
washed,  ignited,  and  weighed,  or  the  moist  filtrate  may  be  dissolved 
upon  the  filter  with  a  little  nitric  acid,  treated  with  sodium  acetate 
and  titrated,  as  described,  with  uranium  solution. 

Example:  14.5  cubic  centimeters  of  the  uranium  solution  are  re- 
quired for  the  precipitate  from  25  cubic  centimeters  of  the  orig- 
inal solution=o.5  gram  superphosphate;  it  contains  then  14.5 X 


FREE  ACID   IN    PHOSPHATES  l8/ 

0.00445=0.0645  gram  P2O5.     Consequently  the  superphosphate 
contains  12.90  per  cent,  of  water-soluble  P2O5. 

Total  Phosphoric  Acid. — Twenty  grams  of  the  superphosphate 
are  boiled  with  50  cubic  centimeters  of  hydrochloric  acid  of  from 
16°  to  18°  Beaume  for  about  10  minutes  and,  after  cooling,  made 
up  to  one  liter  with  water  and  filtered.  Twenty-five  cubic  centi- 
meters of  the  filtrate  are  treated  with  10  cubic  centimeters  of 
Joulie's  citrate  solution,  a  few  pieces  of  filter  paper  thrown  in. 
15  cubic  centimeters  of  magnesia  mixture  added,  and  the 
whole  thoroughly  stirred.  After  standing  two  hours  the  contents 
of  the  flask  are  filtered,  the  precipitate  is  washed  with  dilute 
ammonia,  and  the  filter  and  the  precipitate  are  placed  in  a  platinum 
crucible.  The  crucible  is  heated  slowly  until  the  moisture  is  driv- 
en off  and  the  filter  burned.  Then  the  temperature  is  gradually 
raised  to  a  white  heat.  The  residue  is  cooled  and  weighed. 

Example :  The  precipitate  weighs,  after  the  subtraction  of  the 
filter  ash,  0.1390  gram;  then  the  superphosphate  contains  13.90 
X 2X0-64=  1 7. 79  per  cent,  phosphoric  acid. 

160.  Determination  of  Free  Acid  in  Phosphates  for  Technical 
Purposes. — A  speedy  and  approximately  accurate  method  of 
determining  free  phosphoric  acid  in  superphosphates  is  useful  in 
technical  work,  and  for  this  purpose  Gerhardt  has  proposed  the 
following  process.30  There  are  valid  objections  to  both  the  meth- 
ods in  common  use.  When  the  free  acid  is  extracted  with 
water  and  the  acidity  of  the  extract  determined  by  titration  with 
an  alkali,  the  end  reaction  is  obscured  by  the  separation  of  acid 
calcium  phosphate,  CaHPO4.  On  the  other  hand,  when  absolute 
alcohol  is  used  to  dissolve  the  acid,  the  separation  is  not  exact 
because  of  the  water  content  of  the  sample,  and  drying  the  sample 
would  cause  a  decomposition  and  the  formation  of  new  com- 
pounds of  the  free  phosphoric  acid.  The  principle  of  the  fol- 
lowing process  is  based  on  the  addition  of  an  excess  of  calcium 
carbonate  to  the  sample  and  the  subsequent  determination  of  the 
undecomposed  portion. 

When  pure  phosphoric  acid  is  shaken  with  calcium  carbonate 
the  following  reaction  takes  place : 

2H3PO4+CaCO3=CO2+H2O+CaH4(PO4)2 

*  Chemiker-Zeitung,  1905,  29  :  178. 


1 88  AGRICULTURAL   ANALYSIS 

The  sulfates  of  iron  and  aluminum  disturb  the  accuracy  of  the 
reaction,  since  they  also  react  with  carbonates.  Inasmuch  as  the 
mineral  phosphates  entering  the  factory  have  been  examined  for 
iron  and  alumina,  the  magnitude  of  this  disturbance  can  be  as- 
certained and  due  allowance  made  therefor,  or  the  iron  may  be 
thrown  out  previous  to  the  determination  by  potassium  ferrocya- 
nid.  The  process  is  conducted  as  follows : 

Twenty  grams  of  the  sample  are  shaken  for  half  an  hour  in  a 
liter  flask  with  water,  and  one  gram  of  ferrocyanid  of  potash  dis- 
solved in  water  added  thereto,  the  flask  filled  to  the  mark,  shaken, 
and  the  contents  poured  on  a  filter.  To  100  cubic  centimeters  of 
the  filtrate  a  known  weight  of  calcium  carbonate  is  added,  stirred 
for  half  an  hour,  the  undecomposed  carbonate  separated  by  filtra- 
tion, washed  with  a  small  quantity  of  water,  dried,  ignited  gently 
and  weighed.  The  quantity  of  calcium  carbonate  thus  determined 
deducted  from  the  whole  amount  used,  represents  the  quantity  de- 
composed by  the  free  acids  and  the  iron  and  aluminum  compounds 
above  noted.  The  constant  error,  due  to  the  last  named  source, 
is  applied  as  a  correction  and  the  quantity  of  free  acid  thus  ap- 
proximately determined. 

The  carbon  dioxid  contained  in  the  residue  above  mentioned 
is  determined  more  rapidly  and  with  greater  precision  by  decom- 
posing it  with  an  acid  and  weighing  or  measuring  the  evolved 
gas. 

The  carbonate  remaining  in  the  residue  may  also  be  determined 
by  titration  as  follows :  The  residue  is  placed  in  a  flask  of  200 
cubic  centimeters  capacity  and  decomposed  with  25  cubic  centime- 
ters of  normal  hydrochloric  acid,  filled  to  the  mark,  shaken  and  the 
contents  poured  through  a  dry  filter.  One  hundred  cubic  centi- 
meters of  the  filtrate  are  titrated  with  half-normal  soda-lye,  using 
methyl  orange  as  indicator.  The  correction  for  iron  and  aluminum 
must  again  be  made,  since  any  iron  and  aluminum  phosphate  which 
is  found  with  the  residue  of  calcium  carbonate  decomposes  cor- 
responding quantities  of  the  hydrochloric  acid.  Since  the  fresh 
superphosphate  always  contains  some  free  sulfuric  acid,  it  is  ad- 
visable to  report  the  result  as  degree  of  acidity,  comprising  therein 
the  free  phosphoric  acid,  the  free  sulfuric  acid  and  all  other  com- 


OSTERSETZER'S  METHOD  189 

pounds  of  an  acid  character  which  react  with  calcium  carbonate 
to  form  carbon  dioxid. 

When  an  aqueous  solution  of  CaH4(PO4)2  and  free  phosphoric 
acid  is  titrated  with  an  alkali  in  the  presence  of  methyl  orange, 
no  precipitate  is  produced ;  and,  therefore,  the  precipitate  in  the 
above  method,  ascribed  to  the  formation  of  CaHPO4,  is  rather  to 
be  accredited  to  the  production  of  a  phosphate  of  iron  or  alumina.37 
The  alcohol  method  of  extraction  is  not,  therefore,  as  Gerhardt 
has  supposed,  inapplicable  because  superphosphate  may  go  into 
solution,  since  this  does  not  interfere  with  the  reaction  when 
methyl  orange  is  used  as  indicator,  but  it  is  to  be  rejected  for 
•other  reasons.  The  errors,  however,  due  to  iron  and  alumina  may 
amount  to  as  much  as  one  or  two  per  cent,  and  are  not  constant. 

Gerhardt  maintains  in  a  later  publication  that  Zockler  is  mis- 
taken respecting  the  non-formation  of  CaHPO4  and  regards  his 
method  as  above  described  as  satisfactory,  especially  when  the 
calcium  carbonate  is  titrated  instead  of  ignited.38 

161.  Ostersetzer's  Method. — The  "free"  acid  in  superphos- 
phates may  consist  of  several  kinds,  free  phosphoric  acid,  free, 
sulfuric  acid  and  acid  phosphates  which  react  as  free  acid.  An 
indicator  that  may  be  used  in  a  purely  technical  way  to  indicate 
the  proportion  of  such  free  acid  to  the  total  acid  present  is  aliz- 
arin sulfonic  acid.39  The  determination  of  total  free  acidity  is 
made  as  follows : 

Dissolve  10  grams  of  superphosphate  in  400  cubic  centimeters 
of  water  in  a  500  cubic  centimeter  flask.  Shake  for  the  usual 
time  and  add  four  cubic  centimeters  of  a  solution  containing  two 
and  a  half  grams  of  alizarin  sodium  sulfonate  in  500  cubic  centi- 
meters of  water.  Complete  the  volume  to  the  mark,  filter,  titrate 
50  cubic  centimeters  of  the  filtrate,  representing  one  gram  of  the 
sample,  with  half -normal  sodium  hydroxid  solution  to  transi- 
tion between  yellow  and  brown,  comparing  with  an  equal  volume 
of  the  original  solution  to  better  distinguish  the  changed  color. 
The  free  acidity  is  calculated  from  the  data  obtained  and  com- 
pared with  the  total  acidity  determined  in  the  usual  way. 

37  Zockler,  Chemiker-Zeitung,  1905,  29  :  226,  338. 

38  Chemiker-Zeitung,  1905,  29  :  276. 

39  Chemical  News,  1905,  91  :  215. 


I9O  AGRICULTURAL  ANALYSIS 

BASIC  PHOSPHATIC  SLAGS 

162.  Uses  of  Basic  Slag. — The  importance  of  basic  Bessemer 
slag,  the  residue  of  the  process  of  manufacturing  steel  by  the  basic 
process  from  ores  rich  in  phosphorus,  is  every  where  acknowledged. 
The  use  of  this  material  in  the  United  States  has  not  been  very  ex- 
tensive, chiefly  for  the  reason  that  practically  none  of  it  is  pro- 
duced in  this  country,  sted  not  being  made  from  phosphatic 
ores.  It  is,  however,  made  in  very  large  quantities  in  Europe, 
and  it  is  stated  that  over  2,000,000  tons  of  it  are  used  annually 
in  Germany  alone  for  manurial  purposes. 

Leavens  has  given  the  following  reasons  for  believing  that 
basic  slag  is  a  superior  quality  of  phosphatic  fertilizer:40 

I.  The  phosphoric  acid  in  basic  slag  is  in  a  form  which  can 
not  revert  or  go  back  to  more  insoluble  forms  when  mixed  with 
the  soil  as  is  the  tendency  with  all  superphosphates. 

II.  The  phosphoric  acid  in  basic  slag  is  not  washed  from  the 
soil  by  the  heavy  rains  and  leached  away  in  the  drainage  waters 
as  is  the  case  with  many  other  phosphates. 

III.  Since  the  phosphoric  acid  in  basic  slag  never  wastes  after 
application  to  the  soil,  it  follows  that  basic  slag  may  be  applied 
at  any  time,  either  fall,  spring,  summer,  or  even  in  winter  without 
danger  of  loss. 

IV.  In  addition  to  its  high  content  of  phosphoric  acid,  the 
large  amount  of  lime  in  basic  slag  greatly  adds  to  its  value.     In- 
stead of  having  a  souring  effect  upon  the  land,  as  do  superphos- 
phates, basic  slag  on  account  of  its  strong  alkaline  reaction  sweet- 
ens acid  soils  and  restores  them  to  a  productive  condition. 

The  lime  also  possesses  the  valuable  property  of  making  avail- 
able the  potash  already  in  the  soil  and  has  a  similar  effect  on- 
crude  forms  of  organic  nitrogen.  In  addition  to  the  chemical 
effects  already  mentioned,  lime  greatly  improves  the  physical 
quality  of  the  land,  loosening  up  compact  clay  soils,  thus  mak- 
ing them  more  permeable,  and  compacting  light  sandy  soils  ren- 
dering them  more  retentive  of  moisture  and  plant  food. 

V.  Basic  slag  also  contains  a  considerable  amount  of  magnesia 
which  is  extremely  valuable  in  changing  crude  forms  of  plant 

40  Basic  Slag  and  its  Uses,  1906  :  5. 


USES   OF    BASIC   SLAG  191 

foods  in  the  soil  into  forms  which  the  plant  may  take  up  readily. 
So  powerful  is  its  action  in  this  direction  that  it  is  often  spoken 
of  as  "a  chemical  plow." 

VI.  The  large  amount  of  iron  in  the  basic  slag  should  not  be 
overlooked.     "Iron,"  says  Prof.  Sorauer,  in  his  excellent  treatise 

on  the  physiology  of  plants,  "is  necessary  in  the  building  of  chloro- 
phyll," the  substance  that  gives  the  green  color  to  all  foliage 
"As  it  is  the  function  of  chlorophyll  to  form  new  plastic  material 
under  the  influence  of  the  sunlight,  it  is  natural  that  the  absence 
of  iron,  which  is  shown  by  the  paleness  of  the  leaves,  should  cause 
a  cessation  of  assimilation." 

This  accounts  for  the  deep  green  color  and  splendid  healthy 
condition  of  the  foliage  of  the  plants  and  trees  fertilized  with 
basic  slag. 

VII.  In  addition  to  all  of  the  above,  basic  slag  commends  itself 
strongly  on  account  of  the  high  degree  of  availability  to  plants 
possessed  by  its  phosphoric  acid.     While  little  or  none  of  its 
phosphoric  acid  is  soluble  in  pure  distilled  water,  it  is  soluble 
in  the  secretions  of  the  plant  roots  which  feed  upon  it  readily. 

Experiments  indicate  that  the  total  phosphoric  acid  of  basic 
slag  is  practically  as  effective  as  the  available  phosphoric  acid 
of  acid  phosphate.41 

It  should  be  borne  in  mind  that  this  high  degree  of  availability 
is  not  due  to  any  treatment  of  the  basic  slag  with  sulfuric 
acid.  There  is  a  marked  reaction  all  over  the  country  against  using 
acidulated  fertilizers,  as  their  continued  use  under  improper  con- 
ditions has  rendered  many  thousands  of  acres  of  valuable  land 
infertile. 

The  average  total  results  show  that  insoluble  phosphoric  acid, 
that  is  phosphates  which  have  not  been  treated  or  dissolved  in 
sulfuric  acid  (oil  of  vitriol),  have  more  pounds  of  crop,  both 
straw  and  marketable  grain,  than  the  phosphoric  acid  in  the 
soluble  and  reverted  forms ;  that  is,  in  phosphates  which  have 
been  dissolved  in  sulfuric  acid.42 

VIII.  The  comparative  low  cost  of  basic  slag  with  resulting 

41  Ohio  State  Agricultural  Experiment  Station,  Bulletin  100,  1899  :  137. 
41  Maryland  Agricultural  Experiment  Station,  Bulletin  68,  1900  :  28. 


192  AGRICULTURAL  ANALYSIS 

economy  in  crop  production,  is  a  matter  that  should  appeal  to 
every  practical  farmer. 

Slag  phosphate  plots  produced  a  greater  yield  and  at  a  less 
cost  than  the  average  of  the  soluble  phosphoric  acid  plots  and 
the  bone  meal  plots.  All  yields  were  produced  at  less  cost  with 
slag  phosphates  than  with  bone  meal.43 

IX.  While  basic  slag  generally  should  not  be  mixed  with  mate- 
rials containing  nitrogen  in  organic  forms  such  as  dried  blood, 
ground  bone,  dried  fish  or  tankage,  many  highly  desirable  and 
splendid  combinations  of  it  with  nitrate  of  soda  and  potash  salts 
may  be  made. 

By  varying  the  amount  of  nitrate  of  soda  and  potash  salts  mixed 
with  the  slag,  fertilizers  adapted  for  use  on  all  of  our  leading 
crops  may  be  prepared. 

Wheeler  states  that  basic  slag  is  an  effective  source  of  phos- 
phoric acid  for  use  upon  all  kinds  of  soils,  and  on  account  of 
its  lime  it  is  of  special  promise  in  the  reclamation  of  exhausted 
acid  soils,  particularly  such  as  are  rich  in  organic  matter,  like 
many  marsh  or  muck  soils.44 

Basic  slag  has  been  found  useful  for  peaches,  apples,  grapes, 
oranges,  and  fruits  in  general,  and  for  all  the  cereals.  It  has 
also  proved  very  beneficial  to  clover,  alfalfa,  and  the  grasses ;  in 
fact,  all  kinds  of  crops  which  are  benefitted  by  phosphatic  fertil- 
izers respond  more  readily  to  the  fertilizer  when  in  the  shape  of 
basic  slag.  Since  it  is  quite  likely  that  it  may  come  into  much 
more  general  use  in  this  country,  a  detailed  study  of  the  methods 
of  determining  its  value  is  advisable. 

163.  History  and  Manufacture. — The  basic  process  for  the  man- 
ufacture of  Bessemer  steel  is  known  in  Europe  as  the  Thomas 
or  Thomas  and  Gilchrist  process,  and  the  slags  rich  in  phosphate, 
one  of  the  waste  products  of  the  process,  are  known  by  the 
same  name.  In  this  country  all  the  phosphatic  slags  which  have 
been  made  in  the  manufacture  of  steel  have  been  obtained  work- 
ing chiefly  under  the  patents  of  Reese,  and,  when  prepared  for  the 
market,  are  known  as  odorless  phosphate.  The  only  places  where 

48  Maryland  Agricultural  Experiment  Station,  Bulletin  68,  1900  :  28,  29. 
44  U.  S.  Department  of  Agriculture,  Farmers'  Bulletin  77,  1905  :  18. 


PROCESS  OF   MANUFACTURE  IQ3 

these  slags  have  been  made  in  this  country  are  Pottstown,  Penn- 
sylvania and  Troy,  New  York.  Comparatively  small  quantities 
have  been  manufactured  and  the  industry  has  not  assumed  any 
commercial  importance.  In  Europe  they  are  extensively  manu- 
factured in  England,  France  and  Germany,  and  their  use  for 
agricultural  purposes  has  increased  until  it  is  quite  equal  to  that 
of  superphosphates. 

The  quantity  of  basic  slag  manufactured  in  Germany  in  1893 
was  750,000  tons;  in  England  160,000;  in  France  115,000,  making 
the  total  production  of  central  Europe  about  1,000,000,  a  quantity 
sufficient  to  fertilize  nearly  5,000,000  acres.  During  the  year 
1907  it  is  estimated  that  German  agriculture  made  use  of  from 
1,500,000  to  1,600,000  tons  of  basic  phosphate  slags.  The  total 
output  of  basic  slag  is  undoubtedly  not  far  from  2,000,000  tons. 
The  total  production  of  basic  slag  is  therefore  approximately 
cne-half  of  that  of  crude  phosphates. 

The  following  table  in  metric  terms  shows  the  estimated  pro- 
duction of  crude  phosphates  for  the  whole  world  for  1906  and 
1907  :45 

1907  1906 

United  States 1,917,000  2,052,000 

Tunis 1,040,000  758,000 

Algeria 325,000  302,000 

South  Sea  Islands 300,000  250,000 

France 375, ooo  425,000 

Belgium 180,000  155,000 

All  other  places 100,000  100,000 

4,237,000  4,042,000 

164.  Process  of  Manufacture. — The  principle  of  the  process 
depends  upon  the  arrangement  of  the  furnaces,  by  means  of 
which  the  phosphoric  acid  in  the  iron  ore  or  pig  iron  is  caused  to 
combine  with  the  lime,  which  is  used  as  a  flux  in  the  converters 
A  general  outline  of  the  process  is  as  follows : 

The  pigs,  which  contain  from  two  to  four  per  cent,  of  phos- 
phorus, are  melted  and  introduced  into  a  Bessemer  converter  lined 
with  dolomite  powder  cemented  with  coal-tar,  into  which  has 
previously  been  placed  a  certain  quantity  of  freshly  burned  lime. 

45  Der  Saaten-,  Diinger-und  Futtermarkt,  1908,  No.  7  :  205. 
7 


194  AGRICULTURAL   ANALYSIS 

For  an  average  content  of  three  per  cent,  of  phosphorus  in  the 
pig  iron,  from  15  to  20  pounds  of  lime  are  used  for  each  100 
pounds  of  pig  iron.  As  soon  as  the  melted  pig  iron  has  been 
introduced  into  the  converter,  the  air-blast  is  started,  the  con- 
verter placed  in  an  upright  position,  and  the  purification  of  the 
mass  begins.  The  manganese  in  the  iron  is  converted  into  oxid, 
the  silicon  into  silica,  the  carbon  into  carbon  dioxid  and  oxid, 
and  the  phosphorus  into  phosphoric  acid. 

By  reason  of  the  oxidation  processes,  the  whole  mass  suffers  a 
rise  of  temperature  amounting  in  all  to  about  700°  above  the  tem- 
perature of  the  melted  iron.  At  this  temperature  the  lime  which 
has  been  added,  melts  and,  in  this  melted  state,  combines  with  the 
phosphoric  acid,  and  the  liquid  mass  floats  upon  the  top  of  the 
metallic  portion,  which  has  by  this  process  been  converted  into 
steel. 

As  soon  as  the  process,  which  occupies  only  about  15  min- 
utes, is  completed,  the  fused  slag  is  poured  off  into  molds,  al- 
lowed to  cool,  broken  up,  and  ground  to  a  fine  powder.  For  each 
five  tons  of  steel  which  are  made  in  this  way,  about  one  ton  of 
basic  slag  is  produced. 

In  another  process,  in  order  to  make  a  slag  richer  in  phos- 
phoric acid,  a  lime  is  employed  which  contains  a  considerable 
percentage  of  phosphate.  Although  the  slag  thus  produced  is 
richer  in  phosphoric  acid,  it  is  doubtful  whether  it  is  any  more 
available  for  plant  growth  than  that  made  in  the  usual  way  with 
lime  free  from  phosphoric  acid.  In  other  words,  when  a  basic 
slag  is  made  with  a  lime  free  from  phosphoric  acid,  nearly  the 
whole  of  the  phosphoric  acid  is  combined  as  tetrabasic  calcium 
phosphate.  On  the  other  hand,  when  the  lime  employed  con- 
tains some  of  the  ordinary  mineral  phosphate,  the  basic  slag  pro- 
duced becomes  a  mixture  of  this  mineral  phosphate  with  the 
tetracalcium  salt.  The  mineral  phosphate  is  probably  not  ren- 
dered any  more  available  than  it  was  before. 

It  is  easily  seen  from  the  above  outline  of  the  process  of  man- 
ufacture that  basic  slags  may  have  a  very  widely  divergent  com- 
position. When  made  from  pig  iron  poor  in  phosphorus,  the  slag 
will  have  a  large  excess  of  uncombined  lime  and  consequently  the 


TETRACALCIUM   PHOSPHATE  195 

content  of  phosphoric  acid  will  be  low.  When  made  from  pigs 
rich  in  phosphorus  there  may  be  a  comparative  deficiency  of  iron 
in  the  slag,  and  in  this  case  the  content  of  tetrabasic  calcium  phos- 
phate would  be  unusually  high. 

It  is  found  also  that  the  content  of  iron  in  the  slag  varies 
widely.  In  general,  the  greater  the  content  of  iron  the  harder 
the  slag  and  the  more  difficult  to  grind.  If  the  pig  iron  contain 
sulfur,  as  is  often  the  case,  this  sulfur  is  found  also  in  the  slag  in 
combination  with  the  lime,  either  as  a  sulfid  or  sulfate. 

No  certain  formula  can  therefore  be  assigned  to  basic  slags  and 
the  availability  of  each  one  must  be  judged  by  its  chemical  com- 
position. 

165.  Composition  of  Slag  Phosphate. — The  slags  produced  by  the 
method  above  outlined  may  be  amorphous  or  crystalline.     When 
large  masses  are  slowly  cooled  the  interior  often  discloses  a  crys- 
talline composition.     In  some  samples  analyzed  in  the  labora- 
tory of  the  Division  of  Chemistry  the  crystals  were  found  to  be 
of  two  forms,  viz.,  acicular  and  tabular.46     They  had  the  follow- 
ing composition : 

CALCULATED  PER  CENTS.  AS 

CaO.          FeaO3.    A1.O3.       MgO.        V8OS.  PSO5.  SiOz. 

Acicular  crystals 42.69       20.98      3.71       0.49      0.18  27.06  4.96 

Tabular  crystals 53.61         9.64      0.91       0.08        ...  33.92  1.75 

These  data  show  that  the  two  sets  of  crystals  belong  to  two 
distinct  mineral  forms.  The  presence  of  vanadium  in  one  of  the 
samples  is  worthy  of  remark,  and  leads  to  the  suggestion  that  in 
the  slags  made  of  phosphoriferous  pigs  may  be  found  any  of  the 
rare  metals  which  may  exist  in  the  ores  from  which  the  pigs  were 
made.  The  amorphous  portions  may  have  a  widely  varying  com- 
position and  consequent  variable  content  of  phosphoric  acid.  In 
all  good  slags,  however,  whether  in  crystalline  form  or  as  amor- 
phous powder,  the  lime  and  phosphoric  acid  will  be  found  com- 
bined as  tetracalcium  phosphate  (Ca4P2O9). 

1 66.  Molecular  Structure  of  Tetracalcium  Phosphate. — Several 
theories  have  been- advanced  in  respect  of  the  atomic  arrange- 
ment of  the  elements  contained  in  a  molecule  of  tetracalcium 
phosphate.    It  must  be  confessed  that  so  little  is  known  concern- 

48  Journal  of  Analytical  and  Applied  Chemistry,  1891,  5  :  685. 


196  AGRICULTURAL  ANALYSIS 

ing  the  reactions  of  this  body  as  to  make  theories  of  its  constitu- 
tion largely  visionary.  But  the  existence  in  definite  crystalline 
form  of  this  salt  shows  that  it  is  not  merely  an  intimate  mechan- 
ical mixture,  but  a  true  molecular  form.  As  a  type  of  the  sup- 
posed arrangement  of  its  particles,  the  graphic  formula  proposed 
by  Kormann  may  be  consulted ;  viz., 

O— Ca , 

PO— (X 
\      /Ca 
(X 

6 

Nca 
PO— O/ 

\                      I 
O— Ca 1 

The  crystals  of  this  salt,  as  may  be  seen  by  inspection  of  the 
analytical  data,  contain  other  bodies  than  calcium,  oxygen  and 
phosphorus.  It  would  be  of  interest  to  push  the  investigation 
of  their  constitution  further  and  see  if  crystals  of  pure  tetracal- 
cium  phosphate  could  be  obtained,  and  under  what  conditions 
they  would  be  contaminated  by  other  metallic  oxids.  Usually, 
by  the  color  of  the  crystals,  it  will  be  easy  to  determine  some- 
thing of  the  nature,  if  not  the  extent,  of  the  contamination. 

167.  Solubility  of  Phosphatic  Slags. — The  high  agricultural 
value  of  basic  slags  led  to  an  early  study  of  their  solubility  in 
ammonium  citrate,  citric  acid,  and  other  organic  solutions.  Even 
finely  ground  mineral  phosphates  and  bones  are  soluble  to  some 
extent  in  ammonium  citrate,  as  was  pointed  out  as  long  ago  as 
i882.47  The  most  common  solvents  for  basic  slags  are 
ammonium  citrate  and  citric  acid.  The  ammonium  citrate  should 
be  the  same  as  that  used  for  the  determination  of  reverted  phos- 
phoric acid  and  the  citric  acid  solution  commonly  used  contains 
five  grams  in  a  hundred  cubic  centimeters.  The  slags  of  dif- 
ferent origin  and  even  of  different  age  vary  greatly  in  respect  of 
the  quantity  of  soluble  matter  they  contain.  It  is  believed,  how- 
ever, that  a  very  fair  idea  of  the  agricultural  value  of  a  slag 
47  Wiley,  Journal  of  Analytical  and  Applied  Chemistry,  1889,  3  :  413. 


SOLUTION  OF  PHOSPHATIC  SLAGS  IQ7 

may  be  obtained  by  determining  its  degree  of  solubility  in  one  of 
the  menstrua  named. 

1 68.  Separation  by  Sifting. — The  relative  availability  of  a  slag, 
as  in  the  case  of  a  mineral  phosphate,  is  determined  very  largely 
by  the  percentage  of  fine  material  it  contains.     Sieves  of  varying 
apertures  are   used  to   determine   this   percentage.     A  one-half 
millimeter  or  a  one-quarter  millimeter  circular  aperture  is  best, 
and  the  percentage  of  the  total  material  passing  through  is  deter- 
mined.   A  method  used  in  Germany  consists  in  sifting  the  slag  in 
a  sieve  20  centimeters  in  diameter,  the  meshes  of  which  are  from 
0.14  to  0.17  millimeter  square  and  which  measure  diagonally  from 
0.22  to  0.24  millimeter. 

169.  Solution  of  Phosphatic  Slags. — Sulfuric    acid     has    been 
found  to  be  an  excellent  solvent  for  basic  slags  preparatory  to  the 
determination  of  total  phosphoric  acid.     There  is,  however,  no 
unanimity  of  opinion  concerning  the  best  method  or  means  of 
solution.    Aqua  regia  and  nitric  acid  are  objected  to  because  they 
may  convert  any  phosphorus  in  combination  with  the  iron  into 
phosphoric  acid  and  thus  increase  the  quantity  present.48     But 
iron  phosphid  is  seldom  found  in  slags,  and  therefore  this  objec- 
tion is  not  always  tenable.     Sulfuric  acid  has  also  been  deemed 
objectionable  because  the  gypsum  separated  is   likely  to  carry 
with  it  some  of  the  other  substances  to  be  determined. 

Hydrochloric  acid  is  also  excluded  by  some  from  the  list  of  sol- 
vents because  it  dissolves  so  many  of  the  foreign  elements  in  the 
slag  and  thus  tends  to  complicate  the  subsequent  determinations, 
especially  of  magnesia.  Besides,  a  hydrochloric  acid  solution  is 
not  suited  to  the  use  of  the  citrate  method  formerly  much  em- 
ployed in  the  determination  of  total  phosphoric  acid.  When 
hydrochloric  acid  is  used,  moreover,  the  dissolved  silica  must  be 
removed  and  thus  the  time  required  for  making  a  phosphoric 
acid  determination  is  much  increased. 

If  the  sample  be  sufficiently  fine  the  occlusion  of  undissolved 
phosphate  particles  by  the  gypsum  formed  when  sulfuric  acid  is 
used  is  not  to  be  feared,  and  the  disturbance  of  volume  by  the 
gypsum  is  nearly  constant  and  can  be  allowed  for.  When 

48  von  Reis,  Zeitschrift  fur  angewandte  Chemie,  1888,  1  :  354. 


198  AGRICULTURAL  ANALYSIS 

five  grams  of  slag  are  used  the  mean  volume  of  gypsum  in  the 
solution  is  about  two  cubic  centimeters. 

170.  Estimation  of  Total  Acid. — In  the  determination  of  total 
phosphoric  acid  in  a  slag,  25  cubic  centimeters  of  the  strongest 
sulfuric  acid  are  placed  in  an  erlenmeyer  having  a  wide  neck, 
and  with  careful  shaking  five  grams  of  the  fine  slag  meal  grad- 
ually added.     The  flask  is  heated  over  a  naked  flame  until  solu- 
tion is  complete.    When  the  mass  is  cold  it  is  washed  into  a  quar- 
ter liter  flask ;  again  allowed  to  cool,  filled  with  water  to  the  mark, 
and  two  cubic  centimeters  of  water,  corresponding  to  the  volume 
of  gypsum  undissolved,  are  added,  well  mixed,  and  filtered.     In 
50  cubic  centimeters  of  the  filtrate,  the  phosphoric  acid  is  deter- 
mined by  either  the  molybdate  or  citrate  methods  already  de- 
scribed. 

171.  Alternate  Method. — The  following  method  may  also  be 
used :    Ten  grams  of  the  substance  are  heated  with  50  cubic  cen- 
timeters of  concentrated  sulfuric  acid  until  white  vapors  have 
been  evolved  for  some  time.     The  operation  lasts  for  about  15 
minutes  and  can  be  carried  on  in  a  half-liter  flask  or  in  a  por- 
celain  dish.     Without  regarding  the   undissolved   material,   the 
volume  of  the  liquid  is  now  made  up  to  half  a  liter  and  filtered. 
The  filtered  liquid  becomes  turbid  after  some  time  through  the 
separation  of  calcium  sulfate,  but  this  turbidity  should  not  be 
regarded.     To  50  cubic  centimeters  of  the  solution,  correspond- 
ing to  one  gram  of  substance,  20  cubic  centimeters  of  citric  acid 
(500  grams  citric  acid  to  the  liter)   are  added,  and  it  is  after- 
wards nearly  neutralized  by  the  addition  of   10  per  cent,  am- 
monia and  the  liquid,  which  is  warmed  by  this  operation,  cooled. 
There  are  added  25  cubic  centimeters  of  the  ordinary  magnesium 
chlorid  mixture  and  the  solution  stirred  until  turbidity  is  pro- 
duced, one-third  of  its  volume  of  10  per  cent,  ammonia  added, 
and  again  stirred  for  about  a  minute  to  promote  precipitation. 

Instead  of  the  addition  of  the  citric  acid  and  ammonia,  am- 
monium citrate  prepared  as  follows  may  be  added:  Fifteen  hun- 
dred grams  of  citric  acid  are  dissolved  with  water,  made  up  to 
three  liters,  five  liters  of  24  per  cent,  ammonia  and  seven  liters 


HALLE  METHOD  FOR  BASIC  SLAG  199 

of  water  added.  The  rest  of  the  operation  is  carried  on  in  the 
usual  manner. 

172.  Halle  Method  for  Basic  Slag. — The  total  phosphoric  acid 
is  estimated  at  the  Halle  Station  by  the  following  process  :49 

Ten  grams  of  the  substance  are  moistened  in  a  porcelain  dish 
with  a  few  drops  of  water  and  about  five  cubic  centimeters  of  a 
one  to  one  solution  of  sulfuric  acid  added,  and  after  the  mass  has 
hardened,  which  takes  place  very  soon,  50  cubic  centimeters  of 
concentrated  sulfuric  acid  are  added  and  stirred  with  a  glass  rod 
until  evenly  distributed  throughout  the  whole  mass.  In  stir- 
ring this  mixture  the  greatest  care  must  be  taken,  otherwise  some 
of  the  substance  will  remain  attached  to  the  sides  of  the  dish, 
which  during  later  heating  would  cause  loss  through  spurting. 
The  complete  solution  takes  place  after  a  few  hours  heating  on 
a  sand-bath.  During  the  cooling,  the  jelly-like  mass  must  be 
stirred  with  a  glass  rod,  and  after  it  is  cool,  by  means  of  a  wash- 
ing bottle,  gently  along  the  sides  of  the  dish,  water  is  added,  and 
when  the  mixture  becomes  hot  it  is  again  cooled  and  washed 
into  a  half-liter  flask,  which  is  made  up  to  the  mark  at  a  tem- 
perature of  1 7°. 5  and  filtered.  When  the  acid  filtrate  stands  for 
some  time  there  is  often  a  separation  of  gypsum  that,  however, 
does  not  in  any  way  influence  the  subsequent  analysis,  which  is 
made  in  the  usual  manner. 

Fifty  cubic  centimeters  of  the  filtrate,  representing  one  gram 
of  the  original  substance,  are  placed  in  an  erlenmeyer.  In  the 
case  of  double  superphosphates,  which  often  contain  large  quan- 
tities of  pyrophosphates,  25  cubic  centimeters  of  the  filtrate  just 
obtained,  equivalent  to  0.5  gram  of  the  substance,  are  diluted  with 
75  cubic  centimeters  of  water,  10  cubic  centimeters  of  nitric  acid 
of  1.42  specific  gravity  added,  and  heated  on  a  sand-bath  to  con- 
vert the  pyro-  into  orthophosphates.  The  heating  should  be  con- 
tinued until  the  liquid  is  reduced  to  its  original  volume  of  25 
cubic  centimeters.  The  strongly  acid  liquid  is  saturated  with 
ammonia  and  with  the  addition  of  a  drop  of  rosolic  acid  as  an 
indicator,  again  acidified  with  nitric  acid,  and  treated  as  with 
superphosphates. 

49  Bieler  und  Schneidewind,    Die  agrikultur-chetnische  Versuchsstation 
Halle,  a/S.  ihre  Einrichtung  und  Thiitigkeit,  1892  :  6r. 


2OO  AGRICULTURAL  ANALYSIS 

173.  Dutch  Method  for  Basic  Slag. — Heat     10    grams    of  the 
sample  with  50  cubic  centimeters  of  sulfuric  acid  (1.84  specific 
gravity)  till  white  vapors  are  evolved,  shaking  or  stirring  con- 
stantly.    After  cooling,  make  the  fluid  up  to  500  cubic  centi- 
meters with  water,  taking  no  account  of  the  undissolved  sub- 
stance.    Filter,  and  to  50  cubic  centimeters  of  the  filtrate  add 
100  cubic  centimeters  of  the  ammoniacal  citrate  solution,  and 
after  cooling,  25  cubic  centimeters  of  magnesia  mixture.     Stir  or 
shake  for  a  sufficient  time.     After  the  lapse  of  two  hours  the 
precipitate  is  to  be  separated  by  filtration  and  treated  in  the  usual 
manner. 

174.  Estimation   of  Citrate-Soluble  Phosphoric  Acid  in  Basic 
Slag. — Experience  has  shown  that  the  manurial  value  of  basic 
slags  does  not  depend  alone  on  their  content  of  phosphoric  acid. 
Slags  may  contain  tri-  as  well  as  tetracalcium  phosphate,  and 
even  this  latter  salt  may  exist  in  states  of  differing  availability.    In 
determining  the  availability  of  basic  slag  for  manurial  purposes, 
its  solubility  in  ammonium  citrate  is  considered  the  best  stand- 
ard.   But  this  solubility  will  evidently  be  influenced  by  the  basicity 
of  the  sample  or,  in  other  words,  by  the  quantity  of  lime  present. 
A  slag  rich  in  calcium  oxid  would  deport  itself  differently  with 
a  given  ammonium  citrate  solution  from  one  in  which  the  lime 
had  been  chiefly  converted  into  carbonate.    If  possible,  therefore, 
all  samples  should  be  reduced  to  the  same  state  of  basicity  before 
the  action  of  any  given  solvent  is  determined. 

Wagner  proposes  to  neutralize  the  basicity  of  a  slag  in  the 
following  manner  :50  Five  grams  of  the  slag  are  placed  in  a  half- 
liter  flask,  which  is  then  filled  up  to  the  mark  with  a  one  per  cent, 
solution  of  citric  acid  and  placed  for  half  an  hour  in  a  rotating 
shaker.  After  filtering,  50  cubic  centimeters  are  titrated  with  a 
standard  soda  solution,  using  phenolphthalein  as  indicator.  This 
gives  the  quantity  of  citric  acid  necessary  to  neutralize  the  slag. 
To  a  second  portion  of  five  grams  of  the  sample  in  a  half-liter 
flask  are  added  200  cubic  centimeters  of  water  and  enough  five 
per  cent,  citric  acid  solution  to  neutralize  the  lime,  and  then  200 
cubic  centimeters  of  acid  ammonium  citrate  made  as  indicated 
60  Chemiker-Zeitung,  1894,  18  :  1153- 


WAGNER'S  METHOD  FOR  PHOSPHORIC  ACID  201 

below.  After  filling  to  the  mark  with  water  it  is  shaken  for  half 
an  hour  and  filtered.  To  50  cubic  centimeters  of  the  filtrate  are 
added  100  cubic  centimeters  of  molybdic  solution  and  the  whole 
heated  to  80°.  After  cooling,  the  precipitate  is  filtered  and  the 
phosphoric  acid  estimated  in  the  usual  way. 

The  acid  ammonium  citrate  solution  used  is  made  as  follows: 
Dissolve  1 60  grams  of  citric  acid  with  enough  ammonia  to  repre- 
sent about  28  grams  of  nitrogen  and  make  up  with  water  to  one 
liter. 

The  molybdic  solution  is  made  by  dissolving  125  grams  of 
molybdic  acid  in  a  slight  excess  of  2.5  per  cent,  of  ammonia, 
adding  400  grams  of  ammonium  nitrate,  diluting  to  one  liter  and 
pouring  the  solution  into  one  liter  of  nitric  acid  having  a  specific 
gravity  of  1.19.  After  allowing  to  stand  at  room  temperature 
for  one  day  the  mixture  is  filtered  and  is  then  ready  for  use. 

175.  Wagner's  Method  for  Phosphoric  Acid. — The  directions  giv- 
•en  by  Wagner  for  determining  the  phosphoric  acid  in  slags  and 
raw  phosphates  soluble  in  citrate  solutions  are  the  following:51 
Five  grams  of  the  material  as  it  is  sent  into  commerce,  without 
grinding  or  sifting,  are  placed  in  a  half-liter  flask,  covered  with 
nearly  a  quarter  liter  of  water,  and  then  200  cubic  centimeters  of 
citrate  solution  added,  prepared  as  described  below.  The  flask 
is  filled  to  the  mark  with  water.  The  flasks,  which  are  of  the 
shape  shown  in  the  figure,  are  closed  with  rubber  stoppers,  and 
without  delay  placed  for  half  an  hour  in  a  rotating  apparatus, 
( Fig.  1 1 ) ,  which  is  turned  on  its  axis  from  30  to  40  times  a  min- 
ute. If  a  shaking  apparatus  be  used  instead  of  the  one  men- 
tioned, 200  cubic  centimeters  of  the  citrate  solution  should  be 
placed  in  a  half-liter  flask,  filled  to  the  mark  with  water,  and  the 
contents  poured  into  a  liter  flask  containing  the  phosphate.  This 
flask  should  be  placed  in  a  nearly  horizontal  position  in  the  ap- 
paratus and  the  agitation  be  continued  for  half  an  hour.  On 
removal  from  the  apparatus  the  mixture  is  filtered  and  50  cubic 
centimeters  thereof  treated  with  double  that  quantity  of  molybdic 
solution  at  80°  and  the  precipitate  separated  after  cooling.  The 
precipitate  is  carefully  washed  with  one  per  cent,  nitric  acid  mix- 

"  Chemiker-Zeitung,  1894,  18  :  1933. 


2O2  AGRICULTURAL  ANALYSIS 

tiire,  after  which  the  filter  is  broken  and  the  precipitate  washed 
into  a  beaker  with  two  per  cent,  ammonia  and  the  filter  washed 
therewith  until  about  100  cubic  centimeters  have  been  used.  If 
the  solution  is  turbid  from  the  presence  of  silicic  acid  it  should  be 
precipitated  a  second  time  by  addition  of  molybdic  solution.  The 


Fig.  ii.    Wagner's  Digestion  Apparatus  for  Slags. 

ammoniacal  solution  of  the  yellow  precipitate  is  treated,  drop  by 
drop,  with  constant  stirring,  with  15  cubic  centimeters  of  mag- 
nesia mixture,  and  set  aside  for  two  hours.  The  precipitate  is 
collected,  washed,  ignited  and  weighed  in  the  usual  manner.  The 
direct  precipitation  of  the  phosphoric  acid  by  the  magnesia  solu- 
tion in  presence  of  citrate  is  not  advisable  because  of  the  almost 
general  presence  of  silicic  acid,  which  would  cause  the  results  to- 
be  too  high. 

The  chief  objection  to  this  method  of  Wagner  lies  in  the  fail- 
ure to  control  the  temperature  at  which  the  digestion  with  citrate 
solution  is  made.  Huston  has  shown,  as  will  be  described  further 
on,  that  the  temperature  exercises  a  great  influence  in  digestion 
with  citrate.  Since  the  laboratory  temperature,  especially  in  this 
country,  may  vary  between  10°  and  40°,  it  is  evident  that  on  the 
same  sample  the  Wagner  method  would  give  very  discordant  re- 
sults at  different  seasons  of  the  year  unless  the  digestions  were 
m^de  at  one  temperature.  In  order  to  control  the  temperatures 


ANALYSIS  OF  BASIC  SLAGS  203 

of  digestion,  the  apparatus  devised  by  the  author  may  be  used.52 

176.  Solutions   Employed   in   the    Wagner    Method. — i.    Am- 
monium Citrate. — In  one  liter  there  should  be  exactly  150  grams 
of  citric  acid  and  27.93  grams  of  ammonia,  equivalent  to  23 
grams  of  nitrogen.    The  following  example  illustrates  the  prep- 
aration of  10  liters  of  the  solution:     In  two  liters  of  water  and 
3.5  liters  of  eight  per  cent,  ammonia,  1500  grams  of  citric  acid 
are  dissolved  and  the  cooled  solution  made  up  exactly  to  eight 
liters.*  Dilute  25  cubic  centimeters  of  this  solution  to  250  cubic 
centimeters   and  treat  25  cubic  centimeters   of  this   with  three 
grams  of  calcined  magnesia  and  distill  into  40  cubic  centimeters 
cf  half-normal   sulfuric  acid.     Suppose   the  ammonia  nitrogen 
found  corresponds  to  20  cubic  centimeters  of  fourth-normal  soda- 

ATM.       •    *u      •   u*.  1-4.  ,20.0X0.0035X8000 

lye.     Then  in  the  eight  liters  are  contained  - 

=224  grams  of  ammonia  nitrogen.  In  order  to  secure  in 
the  10  liters  the  proper  quantity  of  ammonia  there  must  be  added 
two  liters  of  water  containing  230 — 224=six  grams  of  nitrogen 
or  7.3  grams  ammonia ;  viz.,  94  cubic  centimeters  of  0.967  specific 
gravity. 

2.  Molybdate  Solution. — Dissolve  125  grams  of  molybdic  acid 
in  dilute  2.5  per  cent,  ammonia,  avoiding  a  large  excess  of  the 
solvent.  Add  400  grams  of  ammonium  nitrate,  dilute  with  water  to 
one  liter  and  pour  the  solution  into  one  liter  of  nitric  acid  of  1.19 
specific  gravity.     Allow  the  preparation  to  stand  for  24  hours  at 
35°  and  filter. 

3.  Magnesia  Mixture. — Dissolve  no  grams  of  pure  crystallized 
magnesium  chlorid  and  140  grams  of  ammonium  chlorid  in  700 
cubic  centimeters  of  eight  per  cent,  ammonia  and  130  cubic  centi- 
meters of  water.     Allow  to  stand  several  days  and  filter. 

177.  Analysis  of  Basic  Slags  by  the  Method  of  the  German 
Agricultural  Experiment  Stations. — The  methods  of  determining 
the  fertilizing  value  of  basic  slags   (Thomas  Meal)   have  been 
studied  by  a  committee  of  the   German  experiment   stations.53 

53  Principles  and  Practice  of  Agricultural  Analysis,  2nd   Edition,  1906, 

1  :  394- 

M  Wagner,  Bestimmung  der  zitronensaureloslichen   Phosphorsaure  in 

Thomasmehlen,  1903. 


2O4  AGRICULTURAL  ANALYSIS 

A  full  statement  of  the  problem  is  given  in  the  first  part  of  the 
report.  In  the  second  part  the  sources  of  error  are  discussed, 
together  with  the  precautions  to  be  observed  in  order  that  these 
errors  may  be  avoided.  In  the  third  part  are  given  the  methods 
of  procedure  which  in  the  opinion  of  the  committee  give  the  most 
acceptable  results. 

These  conclusions  show : 

1.  That  the  use  of  molybdic  acid  in  separating  the  dissolved 
phosphate  is  generally  unnecessary. 

2.  The  phosphate  soluble  in  the  citric  acid  employed  should  be 
precipitated  immediately  after  its  preparation. 

3.  The  precipitation  should  be  accomplished  by  the  iron-citrate- 
magnesia  mixture  to  be  described. 

4.  The  iron-citrate-magnesia    mixture  should  be    added  with 
constant  stirring. 

5.  The  shaker  should  have  a  speed  of  from  250  to  300  revolu- 
tions or  vibrations  a  minute. 

6.  The  temperature  of  the  mixture  should  not  go  above  18°. 

If  the  above  rules  are  followed  results  are  obtained  which  cor- 
respond with  those  secured  by  other  exact  methods.  Even  slags 
which  have  an  exceptional  content  of  silicic  acid  can  be  examined 
by  this  method  with  certainty  in  the  results.  It  may  be  considered, 
therefore,  that  all  the  difficulties  have  been  removed,  and  that  a 
simple  method  of  precipitation  which,  upon  the  whole,  is  much 
more  reliable  than  those  formerly  employed,  can  be  applied  to  the 
examination  of  basic  phosphatic  slags.  The  solutions  employed 
are  as  follows : 

First. — Concentrated  Citric  Acid  Solution,  10  Per  Cent.  Exact- 
ly one  kilogram  of  chemically  pure  crystallized  uneffloresced 
citric  acid  is  dissolved  in  water,  diluted  to  10  liters,  and  for  the 
purpose  of  preventing  the  growth  of  mould  and  other  decom- 
position products,  five  grams  of  salicylic  acid  are  dissolved  in  the 
mixture. 

Second. — Dilute  Citric  Acid  Solution,  Two  Per  Cent.  Exactly 
one  volume  of  the  concentrated  citric  acid  solution,  above  men- 
tioned, is  diluted  with  four  volumes  of  water. 

Third. — Molybdic  Solution.     One  hundred  and  fifty  grams  of 


PREPARATION   OF  THE   CITRIC   ACID   EXTRACT  2O5 

chemically  pure  ammonium  molybdate  are  dissolved  in  about  500 
cubic  centimeters  of  water.  This  solution  is  poured  into  one  liter 
of  nitric  acid,  1.19  specific  gravity,  400  grams  of  ammonium 
nitrate  added  thereto,  and  the  mixture  diluted  with  water  to  two 
liters.  The  solution  is  allowed  to  stand  24  hours  at  about  35° 
temperature  and  filtered. 

Fourth. — Magnesia  Mixture.  One  hundred  and  ten  grams  of 
crystallized  magnesium  chlorid  and  140  of  ammonium  chlorid  are 
dissolved  in  1300  cubic  centimeters  of  water  and  700  cubic  centi- 
meters of  ammonia  water  containing  eight  per  cent,  of  NH3  added 
thereto.  After  standing  several  days  the  solution  is  filtered. 

Fifth. — Citrate-Magnesia  Mixture.  Two  hundred  grams  of 
citric  acid  are  dissolved  in  20  per  cent,  of  ammonia  and  the  vol- 
ume made  up  to  one  liter  with  20  per  cent,  ammonia.  This  solu- 
tion is  mixed  with  one  liter  of  the  magnesia  mixture  described 
under  "  fourth." 

Sixth. — Iron-Citrate-Magnesia  Mixture.  One  liter  of  the 
citrate-magnesia  mixture  described  under  "fifth"  is  mixed  with  10 
cubic  centimeters  of  a  20  per  cent,  ferrous  chlorid  solution. 

Preparation  of  the  Basic  Slag  for  Analysis. — The  basic  slag 
which  is  intended  for  analysis  is  passed  through  a  two 
millimeter  mesh  sieve  in  order  to  remove  any  large  pieces 
which  may  be  present.  All  loss  of  dust  during  this  operation  is 
to  be  carefully  avoided  and  to  this  end  the  sieve  is  to  be  closed 
with  a  well  fitting  cover  and  nicely  adjusted  to  the  vessel  receiv- 
ing the  sifted  material.  Any  residue  remaining  upon  the  sieve  is 
weighed  and  is  excluded  from  analysis,  but  is  included  in  the 
results  on  the  total  sample  in  order  to  determine  the  percentage 
thereof.  Thus  prepared  the  material  will  yield  a  typical  sample 
for  analysis. 

178.  Preparation  of  the  Citric  Acid  Extract. — Five  grams  of 
the  basic  slag,  prepared  as  above,  are  placed  in  a  half-liter  flask 
into  which  previously  five  cubic  centimeters  of  alcohol  has  been 
poured  and  the  flask  filled  with  the  dilute  two  per  cent,  citric  acid 
solution  at  a  temperature  of  17.5°  the  flask  closed  with  a  rubber 
stopper  and  without  delay  placed  in  a  revolving  shaking  apparatus 
rotating  at  from  30  to  40  times  a  minute  for  30  minutes.  The  con- 
tents of  the  flask  are  then  immediately  filtered. 


2O6  AGRICULTURAL  ANALYSIS 

179.  Treatment  of  the  Citric  Acid  Extract. — The    filtrate    ob- 
tained as  above  is  as  soon  as  possible  subjected  to  the  following 
treatment :     Fifty  cubic  centimeters  of  the  filtrate  in  a  beaker  are 
placed  in  a  stutzer  shaking  apparatus,  which  is  set  in  rapid  mo- 
tion from  about  250  to  300  vibrations  per  minute ;  50  cubic  centi- 
meters of  the  iron-citrate-magnesia  mixture,  above   noted,   are 
then  added,    and    with    the    temperature    at    from    14°    to    18° 
the  shaking  is  continued  for  half  an  hour.    The  precipitate  is  put 
in  a  gooch  crucible  or  upon  an  ash-free  filter,  washed  with  two 
per  cent,  ammonia,  ignited  and  weighed  in  the  usual  way.     If 
the  citric  acid  solution  obtained  above  is  exceptionally  light  col- 
ored or  entirely  colorless  the  duplicate  estimation  is  not  made 
according  to  the  described  method,  but  by  the  molybdate  method 
or  by  the  Naumann  method.64 

The  molybdate  method  is  carried  out  as  follows  :  Fifty  cubic  cen- 
timeters in  a  beaker  or  flask  are  treated  with  from  50  to  80  cubic 
centimeters  of  the  molybdic  solution,  above  mentioned,  and 
warmed  in  a  water  bath  to  about  65°.  The  beaker  is  then 
withdrawn  from  the  water  bath,  cooled  and  its  contents  filtered, 
and  the  molybdic  precipitate  carefully  washed  with  a  one  per 
cent,  nitric  acid  solution  and  dissolved  in  about  100  cubic  centi- 
meters of  two  per  cent,  ammonia.  The  ammoniacal  solution,  with 
constant  stirring,  is  treated  with  15  cubic  centimeters  of  the  mag- 
nesia mixture,  the  beaker  covered  with  a  glass  plate  and  set  aside 
for  two  hours.  The  precipitated  ammonium  magnesia  phosphate 
is  collected  upon  an  ash-free  filter  or  gooch,  ashed  with  two 
per  cent,  ammonia,  dried,  the  filter  paper,  if  used,  ashed  over  a 
bunsen  burner  and  finally  ignited  in  a  blast  for  two  minutes, 
cooled  and  weighed. 

180.  Preparation   of   the   Citric   Acid   Extract   of  Basic   Slag. 
—The  details  of  the  preparation  and  treatment  of  the  extract  are 

important.  It  is  self-evident  that  the  citric  acid  solution  with 
which  the  slag  is  treated  must  be  prepared  exactly  as  described, 
and  thus  must  contain  20  grams  of  chemically  pure  crystallized 
uneffloresced  citric  acid  to  the  liter.  For  the  purpose  of  diminish- 
ing the  amount  of  work  it  is  advisable  to  keep  on  hand  a  quantity 
54  Chemiker-Zeitung,  1903,  27  :  12,  27,  120,  155. 


PREPARATION   OF  THE  CITRIC   ACID   EXTRACT  2O? 

of  10  per  cent,  citric  acid  solution,  which  is  preserved  by  the  ad- 
dition of  half  a  gram  of  salicylic  acid  per  liter.  From  this  store 
the  other  solution  of  citric  acid  can  be  prepared.  It  is  important 
that  the  citric  acid  solution  which  is  used,  should  be  as  nearly  as 
possible  at  a  mean  temperature  of  17.5°.  Any  departure  from  this 
temperature  is  apt  to  produce  errors.  For  this  reason,  the  shaking 
machine  should  be  in  a  room  approximately  of  the  same  tem- 
perature. It  is  advisable  to  have  the  apparatus  protected  with 
felt. 

In  pouring  500  cubic  centimeters  of  citric  acid  solution  on  five 
grams  of  the  sample  it  is  sometimes  noticed  that  small  lumps 
of  the  slag  are  produced,  which  resist  for  a  long  while  the  en- 
trance of  the  solvent.  For  this  reason  it  is  advisable  to  use,  pre- 
viously to  the  introduction  of  the  citric  acid  solution,  five  cubic 
centimeters  of  alcohol  into  which  the  sample  of  basic  slag  is 
poured. 

It  is  inadvisable  to  use  a  shaking  apparatus  in  place  of  the  ro- 
tating apparatus  described.  Wagner  uses  a  rotating  apparatus 
made  in  Darmstadt,  which  is  constructed  of  metal  and  driven  by 
a  gas  motor.  The  flasks  which  are  to  be  used  in  the  rotating  ap- 
paratus are  made  especially  for  this  purpose  according  to  the 
specifications  of  Wagner,  and  have  a  neck  diameter  of  at  least 
20  millimeters  and  the  mark  is  at  least  eight  centimeters 
below  the  mouth.  Some  care  must  be  exercised  in  this  matter, 
for  if  the  diameter  of  the  neck  is  too  narrow  or  the  mark  too  high, 
the  movement  of  the  fluid  during  rotation  is  restricted,  and  there- 
by the  results  may  be  influenced.  The  rotating  apparatus  should 
have  a  velocity  of  from  30  to  40  rotations  per  minute,  but  any 
variation  of  the  rate  of  rotation  between  these  two  figures  is 
without  any  marked  influence  upon  the  results. 

The  filtration  ought  to  take  place  immediately  after  the  end  of 
the  30  minutes  rotation,  and  it  is  advisable  to  use  a  folded  filter 
of  sufficient  size  so  that  the  whole  contents  of  the  flask  may  be 
brought  at  once  upon  the  filter.  Small  and  badly  working  filters 
by  reason  of  delay  in  the  filtrations,  can  easily  produce  errors  in  the 
result.  If  the  filtrate  should  be  at  first  turbid,  it  is  thrown  back 
upon  the  filter. 


2O8  AGRICULTURAL   ANALYSIS 

181.  Remarks    on   the    Conduct    of    the    Direct    Precipitation 
Method. — The  citric  acid  extract  of  the  basic  slag  changes  by 
long  standing,  so  far  as  the  external  appearance  is  concerned, 
very  little.     It  remains  for  days  either  completely  clear  or  only 
slightly  turbid,  without  the  production  of  any  precipitate.     In 
spite  of  this,  however,  important  changes  go  on  in  relation  to  the 
application  of  the  direct  precipitation  method,  which  consist  in 
the  fact  that  any  silicic  acid  in  the  extract  passes  over  into  a  pre- 
cipitable  condition  upon  the  addition  of  ammonia  or  ammoniacal 
citrate  solution.     The  precipitability  of  the  silicic  acid  increases 
from  hour  to  hour,  and  it  is  therefore  necessary  to  precipitate  the 
filtrate  extract  immediately,  or  at  longest,  within  an  hour. 

The  precipitability  of  silicic  acid  is  greatly  increased  by  heat. 
The  shaking  apparatus  is,  therefore,  to  be  supplied  with  a  water 
bath  by  which  the  mixtures  during  the  summer  time  may  be 
cooled. 

The  precipitability  of  silicic  acid  is  very  little  immediately  after 
the  citric  acid  solution  of  the  phosphoric  acid  is  made.  The  more, 
therefore,  the  precipitation  of  the  phosphoric  acid  with  the  mag- 
nesia mixture  is  hastened,  the  more  certainly  is  avoided  any  con- 
tamination of  the  precipitate  with  silicic  acid.  The  precipitation 
of  the  phosphoric  acid  is  also  hastened  as  follows : 

a.  If  the  ammoniacal  citrate  solution  is  not  added  first,  and 
then  the  magnesia  mixture,  but  the  mixture  of  both  is  added  to 
the  citric  acid  extract ; 

b.  The  iron-citrate-magnesia  mixture  is  poured  into  the  citric 
acid  extract  in  the  shaking  apparatus,  which  is  already  in  active 
movement ; 

c.  The  shaking  apparatus  is  to  be  placed  in  the  shortest  pos- 
sible time  at  its  maximum  vibration  of  from  250  to  300  vibra- 
tions per  minute. 

The  precipitability  of  the  silicic  acid  is  heightened  through  a 
lack  of  iron  in  solutions  which  are  rich  in  silicic  acid  and  poor  in 
iron,  therefore  a  pure  precipitate  is  obtained  only  when  the  iron- 
citrate-magnesia  mixture  is  employed. 

182.  The  Conduct  of  the  Molybdate  Method. — a.  Great  care  must 


GERMAN  METHOD  FOR  SLAGS  RICH  IN  SILICIC  ACID    '      2OO, 

be  exercised  that  the  reagents  employed  in  the  preparation  of  the 
molybdic  solutions  be  absolutely  pure. 

b.  Molybdic  solutions  before  using  should  be  tested  for  purity 
by  means  of  a  solution  of  disodium  phosphate. 

c.  The  mixture  of  the  citric  acid  extract  and  the  molybdic  solu- 
tion is  to  be  taken  from  the  water  bath  when  the  prescribed 
temperature  has  been  reached.    If  the  time  of  digestion  be  mark- 
edly extended  a  contamination  of  the  precipitate  with  silicic  acid 
arises,  especially  when  the  citric  acid  extract  is  not  in  a  fresh 
condition,    but    only    after    from    six    to    12    hours  standing  is 
treated  with  the  molybdic  solution. 

d.  A  contamination  of  the  molybdic  precipitate  with  the  silicic 
acid  is  recognized  by  the  following:     Slow  solution  of  the  pre- 
cipitate in  ammonia  and  the  production  of  a  solution  not  com- 
pletely clear  or  becoming  only  slowly  so.     Under  these  condi- 
tions the  process  already  advised,  namely,  a  reprecipitation  of 
the  magnesia  precipitate,  is  to  be  applied. 

183.  The  Official  German  Method  for  Slags  Rich  in  Silicic  Acid. 
— When  the  slags  are  very  rich  in  soluble  silicic  acid  the  process 
of  analysis  is  conducted  as  follows:55 

The  sample  is  to  be  tested  for  silicic  acid  by  the  method  of  Kell- 
ner,  which  consists  in  boiling  for  one  minute  50  cubic  centime- 
ters of  the  citric  acid  extract  with  50  cubic  centimeters  of  ammo- 
niacal  citrate  solution  and  allowing  to  stand  for  a  few  minutes.56 
If  there  is  sufficient  silicic  acid  present  to  interfere  with  the  direct 
(Bottcher)  precipitation  of  the  phosphoric  acid,  a  precipitate 
is  separated  which  is  not  entirely  soluble  in  hydrochloric  acid. 
The  ammoniacal  citrate  solution,  employed  above,  contains  in  10 
liters,  iioo  grams  of  nitric  acid,  4000  grams  of  24  per  cent,  am- 
monia, and  water  to  the  mark. 

The  presence  of  a  disturbing  amount  of  silicic  acid  having 
been  thus  determined,  it  is  separated  in  the  following  manner : 
To  loo  cubic  centimeters  of  the  citric  acid  extract  of  the  slag 
3re  added  7.5  cubic  centimeters  of  hydrochloric  acid  of  1.12 
specific  gravity  or  five  cubic  centimeters  of  fuming  hydrochloric 
55  Die  landwirtschaftlichen  Versuchs-Stationen,  1904,  60  :  374;  1905, 

€1  =351- 

58  Chemiker-Zeitung,  1902,  26  :  1151. 


2IO  AGRICULTURAL,  ANALYSIS 

acid  and  the  mixture  evaporated  to  a  thick  sirup,  smelling  of  hy- 
drochloric acid.  To  the  hot  residue,  from  1.5  to  two  cubic  centi- 
meters of  hydrochloric  acid,  1.12  specific  gravity,  are  added,  and 
the  mixture  thoroughly  stirred  and  dissolved  in  enough  water  to 
make  the  volume  100  cubic  centimeters.  The  phosphoric  acid  is 
determined  in  50  cubic  centimeters  of  the  filtrate  by  the  direct 
method. 

The  process  consists  in  adding  50  cubic  centimeters  of  the 
citrate-magnesia  mixture  to  the  same  volume  of  the  filtered  citric 
acid  extract  of  the  slag.  The  magnesia  mixture  contains  550 
grams  of  magnesium  chlorid  and  700  grams  of  ammonium  chlorid 
dissolved  in  3.5  liters  of  eight  per  cent,  ammonia,  and  6.5  liters 
of  water.  The  ammoniacal  citrate  solution  for  mixing  with  the 
magnesia  mixture,  mentioned  above,  contains  2000  grams  of  citric 
acid  dissolved  in  20  per  cent,  ammonia,  and  the  volume  made  up 
to  10  liters  with  the  same  reagent.  Before  use,  equal  parts  of 
the  magnesia  mixture  and  the  ammoniacal  citrate  solution  are 
mixed  together. 

184.  Bottcher  Method. — The  Bottcher  modification  of  the  direct 
citrate  method  of  determining  the  phosphoric  acid  dissolved  from 
basic  slags  by  citric  acid  is  as  follows  :57 

In  50  cubic  centimeters  of  the  solution  of  a  slag  in  citric  acid 
according  to  Wagner's  method,  the  phosphoric  acid  is  thrown 
down  in  the  prescribed  manner  by  magnesium  citrate  solution, 
the  precipitate  collected  on  a  filter,  washed  several  times  with 
five  per  cent,  ammonia,  and  the  moist  filter  ashed.  The  ash  is 
dissolved  in  warm  hydrochloric  acid,  the  dilute  solution  passed 
through  a  small  filter,  washed  with  hot  water,  and  the  phosphoric 
acid  again  precipitated  with  the  citrate  magnesia. 

The  important  point  is  that  after  the  addition  of  the  citrate  of 
magnesia,  the  mixture  be  immediately  vigorously  shaken  and  then, 
without  a  moment's  delay,  filtered.  Even  standing  for  from 
half  an  hour  to  an  hour  may  cause  serious  annoyance  and  intro- 
duce serious  errors  into  the  results. 

The  direct  precipitation  of  the  phosphoric  acid  by  ammoniacal 
citrate  of  magnesia  was  adopted  as  the  official  method  in  the 
57  Chemiker-Zeitung,  1897,  21 1:  168. 


SEPARATION  OF  SILICIC  ACID  211 

general  meeting  of  the  delegates  of  the  German  agricultural  ex- 
periment stations,  at  Cassel,  in  1903,  both  for  slags  and  tricalcium 
phosphates,  and  for  the  general  separation  of  phosphoric  acid.58 

Bottcher,  in  a  later  communication,  expresses  the  opinion  that 
if  the  direct  precipitation  of  the  phosphoric  acid  be  carried  on 
with  all  the  promptitude  which  he  has  recommended,  the  pre- 
vious separation  of  the  silicic  acid,  when  an  excess  has  been  in- 
dicated by  the  Keliner  test,  is  rarely  necessary.59 

The  great  point  to  be  observed  is  that  all  the  manipulations  be 
conducted  without  delay.  The  preliminary  test  by  the  Keliner 
method  is  chiefly  valuable  in  showing  with  what  samples  special 
precautions  are  necessary. 

185.  Separation  of  Silicic  Acid  in  the  Estimation  of  Phosphoric 
Acid  in  Basic  Slag,  Bone  Meal,  Etc.60 — Attention  is  called  by 
Bottcher  to  the  fact  that  after  the  Association  of  Agricultural 
Experiment  Stations  of  the  German  Empire  had  determined  to 
estimate  the  citric-acid-soluble  phosphoric  acid  in  basic  slag  by 
the  direct  precipitation  method  in  all  cases  where  the  preliminary 
test  by  boiling  with  50  cubic  centimeters  of  ammoniacal  citrate 
solution  did  not  show  a  high  content  of  silicic  acid,  the  opinion 
has  again  come  into  consideration  that  the  separation  of  the  silicic 
acid  by  evaporation  with  hydrochloric  acid  is  necessary  with  all 
basic  slags  because  the  direct  precipitation  sometimes  gives  re- 
sults which  are  too  high,  even  if  the  preliminary  test  shows  no 
especially  high  content  of  silicic  acid,  and  the  solutions  very  often 
filter  too  slowly.  Bottcher,  however,  affirms  anew  that  the 
conduct  of  the  direct  precipitation  citrate  method  never  leads  to 
any  difficulties  of  filtration  nor  to  any  differences  in  the  results. 
As  he  pointed  out  in  a  former  place,  and  as  he  has  shown  by 
subsequent  analyses,  which  are  given,  he  has  obtained  absolutely 
correct  results  with  all  normal  basic  slags,  which  with  two  per  cent, 
citric  acid  solution  gave  bright  green  solutions,  even  when  the  pre- 
liminary treatment  has  shown  a  high  content  of  silica.61  In 

58  Die  landwirtschaftlichen  Versuchs-Stationen,  1904,  60  :  221. 

59  Chemiker-Zeitung,  1903,  27  :  247. 

Zeitschrift  fur  angewandte  Chemie,  1904,  1 7  :  988. 

60  Chemiker-  Zeitung,  1905,  29  :  1293. 

61  Chemiker-Zeitung,  1903,  27  :  247. 


212  AGRICULTURAL   ANALYSIS 

all  cases,  however,  the  method  which  he  has  proposed  must  be 
carefully  followed  out,  that  is,  all  the  manipulations  must  follow 
each  other  directly  without  delay,  a  condition  which  is  easily  se- 
cured. If,  on  the  contrary,  the  citric  -acid  extract,  or  the  pre- 
cipitations with  citrate  solution  and  magnesia  mixture,  or  the 
citrate-holding  magnesia  mixture,  are  allowed  to  stand  for  several 
hours,  which,  in  spite  of  the  precise  directions  given,  still  some- 
.times  happens,  it  can  readily  occur  that  large  quantities  of  silicic 
acid  come  down  with  the  phosphoric  acid  precipitate  and  the  re- 
sults are,  in  consequence,  too  high.  In  such  cases  it  is  easy  to  ex- 
plain why  the  precipitated  phosphoric  acids  filter  badly.  In 
carrying  out  of  the  method  in  cases  of  bad  filtration,  it  has  been 
observed  by  Bottcher,  in  the  conduct  of  over  800  determinations, 
that  if  a  solution  filters  badly  it  is  a  proof  that  in  some  way  or 
other  silicic  acid  has  been  precipitated,  and  naturally  in  such  a 
case,  the  silicic  acid  must  be  removed  by  evaporation  with  hydro- 
chloric acid  in  order  that  correct  results  be  obtained. 

Many  comparisons  are  given  by  the  author  of  the  data  obtained 
by  direct  precipitation  and  by  precipitation  after  the  separation 
of  the  silicic  acid.  The  differences  are  in  all  cases  negligible 
between  the  two  methods. 

Following  are  the  data  from  two  samples  in  which  the  magnesia 
pyrophosphate  was  obtained  by  four  different  methods,  namely : 

(1)  Direct  precipitation. 

(2)  Direct  precipitation  after  separation  of  silicic  acid. 

(3)  Direct  precipitation  by  molybdate  method. 

(4)  Direct  precipitation  by  molybdate  method  after  separation 
with  silicic  acid. 

The  data  obtained  are  as  follows : 

Weight  of  Sample  I.  Weight  of  Sample  II. 

Grams.  Grams. 

Method    (i)  0.1472  0.1435 

(2)  0.1466  0.1410 

(3)  0.1475  0.1420 

(4)  0.1476  0.1436 

These  analytical  data  show  that  basic  slags  which  are  not 
capable  of  being  correctly  analyzed  by  the  direct  citrate  precipita- 
tion method  are  of  very  seldom  occurrence.  Nevertheless  a  pre- 


DIRECT  AND  MOLYBDATE  METHODS  213 

liminary  treatment  by  the  citric  acid  test  for  silicic  acid  should 
not  be  omitted,  since  it  is  a  safe  means  of  discovering  those 
samples  which  must  be  treated  with  particular  care. 

186.  Comparison  of  the  Direct  and  the  Molybdate  Method  for  the 
Estimation  of  the  Total  Phosphoric  Acid  in  Basic  Slag,  Bone 
Meal,  Etc.152— V.  Schenke  has  stated  that  the  direct  precipitation 
of  total  phosphoric  acid  in  bone  meal  and  basic  slags,  according 
to  the  method  of  the  Association  of  Agricultural  Experiment 
Stations  of  Germany,  that  is,  direct  precipitation  of  magnesia 
mixture,  gives  from  0.3  to  0.4  per  cent,  less  phosphoric  acid  than 
the  molybdate  method.63  He,  therefore,  considers  it  necessary  that 
the  strongly  acid  phosphate  solution  before  precipitation  with 
magnesia  mixture  should  be  almost  neutralized  and  only  half  the 
quantity,  namely,  50  cubic  centimeters  instead  of  100  cubic  centi- 
meters, should  be  treated  with  the  ammonium  citrate  solution. 
It  has,  however,  already  been  shown  by  the  earlier  data  of 
Maercker  and  Halenke,  as  well  as  by  the  latest  researches  of 
Mach64  that  this  view  of  Schenke  is  not  correct,  and  also  the 
analyses  of  Bottcher  indicate  the  same  fact,  and  that  neutraliza- 
tion of  the  solution  before  the  precipitation  with  the  citrate  solu- 
tion and  the  magnesia  mixture  uther  by  aqua  regia  or  by  sulfuric 
acid  is  not  necessary.65  Bottcher  says  it  is  claimed  by  many  ana- 
lysts that  by  solution  of  bone  meal,  etc.,  with  aqua  regia  and  subse- 
quent direct  precipitation  with  citrate  solution  and  magnesia  mix- 
ture, incorrect  and,  indeed,  higher  results  are  obtained  than 
when  sulfuric  acid  is  used  for  the  solution.  As  a  reason  for 
this  it  is  said  that  the  compensation  for  the  errors  which  take 
place  in  the  aqua  regia  solutions  is  irregular,  according  to  the  kind 
and  quantity  of  the  bases  which  are  present  in  the  solution.  It 
is  also  supposed  that  in  bone  meals  and  other  organic  substances 
by  reason  of  the  incomplete  oxidation  with  aqua  regia,  organic 
acids  are  formed  whose  lime  salts  are  equally  soluble  in  the  am- 
monium citrate  solution  and  are,  therefore,  carried  down  by  the 
precipitate.  In  the  solutions  by  sulfuric  acid  the  proportions  re- 

(W  Chemiker-Zeitung,  1905,  29  :  1294. 

63  Die  landwirtschaftlichen  Versuchs-Stationen,  1905,  62  :  3. 

64  Die  landwirtschaftlichen  Versuchs-Stationen,  1905-6,  63  :8i. 

65  Chemiker-Zeitung,  1905,  29  :  1294- 


214  AGRICULTURAL   ANALYSIS 

main  essentially  more  favorable,  since  not  all,  but  always  an  equal- 
ly proportionate  part,  of  the  bases  go  into  solution. 

In  order  to  prove  whether  these  objections  against  the  solution 
with  aqua  regia  were  correct,  Bottcher  in  different  bone  meals 
carried  out  the  estimation  of  the  total  phosphoric  acid,  both  by 
solution  with  aqua  regia  and  with  sulfuric  acid.  In  samples  of 
50  cubic  centimeters  of  the  acid  phosphate  solution  the  phosphoric 
acid  was  precipitated,  according  to  the  methods  of  the  German 
association,  by  direct  precipitation  with  citrate  solution  and 
magnesia  mixture,  and  in  other  samples  of  50  cubic  centimeters 
according  to  the  modification  of  Schenke,  that  is,  the  approximate 
neutralization  of  the  solutions  with  ammonia  before  the  addition 
of  the  citrate  solution  and  magnesia  mixture. 

The  data  which  were  obtained  show  that  the  objections  urged 
by  Schenke  are  not  well  founded  and  that  in  the  case  of  bone 
meals,  etc.,  as  good  results  were  obtained  by  solution  with  aqua 
regia  as  with  sulfuric  acid.  If  sometimes  lower  results  are  ob- 
tained after  solution  in  sulfuric  acid,  the  reason  lies  perhaps  in 
the  fact  that  after  the  treatment  of  strong  sulfuric  acid  phosphate 
solutions  with  ammoniacal  citrate  solution  a  marked  heating  of  the 
mixture  takes  place  and  it  is  not  sufficiently  cooled  before  the 
addition  of  the  magnesia  mixture.  This  subsequent  cooling  be- 
fore precipitation  is  necessary  since  otherwise  the  results  fall 
too  low. 

187.  Estimation  of  Phosphoric  Acid  in  Slags. — The  further 
discussion  of  determining  the  phosphoric  acid  in  slags  by  the  cit- 
rate method  by  Schenke  and  Mach  has  introduced  certain  modi- 
fications of  an  unimportant  character,  in  the  process.88 

In  the  estimation  of  the  citrate-soluble  phosphoric  acid  in  slags 
by  the  molybdate  method,  Schenke  follows  in  general  the  Wagner 
method,  heating  the  precipitate  only  15  to  30  minutes  in  a  water 
bath  at  80°  or  90°  and  allowing  to  cool  for  two  or  three  hours. 
By  this  method  the  precipitation  of  molybdic  acid  is  most  cer- 
tainly avoided  and  a  bright  and  clear  solution  of  the  precipitate 
is  easily  secured  in  cold  dilute  ammonia.  Impurities  due  to 
silicic  acid  are  also  avoided. 

88  Die    landwirtschaftlichen    Versuchs-Stationen,    1905,    62  :  3  ;    1906, 
64  :  87. 


TOTAL  PHOSPHORIC  ACID  IN   BASIC   SLAGS 

In  all  cases  the  complete  precipitation  of  phosphoric  acid  is 
rendered  certain  by  an  addition  of  molybdate  solution  to  the  ni- 
trate. 

Schenke  calls  attention  to  the  important  point  that  if  the  method 
of  the  German  stations  is  strictly  followed  with  the  citrate  method 
of  determination  no  precipitate  at  all  of  phosphoric  acid  is  ob- 
tained where  only  very  small  quantities  are  present.  This  is  the 
case  both  with  certain  soils  which  contain  only  a  trace  of  phos- 
phoric acid  and  certain  cattle  foods.  In  such  cases  the  above 
stated  molybdate  method  gave  agreeing  results  even  in  these  small 
quantities.  The  reason  for  this  is  said  to  be  the  increased  solu- 
bility of  the  precipitate  of  magnesium  ammonium  phosphate  in 
the  double  quantity  of  ammonium  citrate  solution  which  is  used. 

188.  Estimation  of  Total  Phosphoric  Acid  in  Basic  Slags  Solu- 
ble in  Citric  Acid  Solutions. — Since  the  value  of  basic  slag  is  no 
longer  determined  solely  by  the  total  content  of  phosphoric  acid 
therein,  the  agricultural  analysts  have  never  been  able  to  agree 
upon  a  satisfactory  plan  for  the  valuation  of  phosphoric  acid 
available  for  plant  growth.  The  use  of  citric  acid  solutions  for 
dissolving  the  supposed  available  phosphoric  acid  is  the  one  which 
is  most  commonly  employed.  It  is  easily  seen,  however,  that 
the  activity  of  a  solution  of  this  kind  depends  upon  the  amount  of 
free  lime  in  the  sample,  its  state  of  subdivision,  the  temperature 
at  which  the  solution  takes  place  and  the  agitation  to  which  the 
mixture  is  subjected.  The  disturbing  influence  of  silicic  acid  is 
also  to  be  taken  into  consideration  and  this  has  been  fully  dis- 
cussed. Mach  has  found  in  a  large  number  of  determinations 
that  the  Wagner  method  in  most  cases  gives  satisfactory  results 
while  the  direct  precipitation  by  the  Bottcher  method  sometimes 
fails,  and  in  its  present  form  is  not  to  be  regarded  as  reliable  as 
the  German  experiment  station  method  with  previous  separa- 
tion of  silica.67  It  is  concluded,  therefore,  that  as  a  result  of  the 
study  of  all  the  various  methods,  the  one  which  is  based  upon  the 
previous  separation  of  the  silicic  out  of  the  citric  acid  extract  is 
the  most  reliable. 

In  a  study  of  the  different  forms  of  precipitation  of  total  phos- 

67  Die  landwirtschaftlichen  Versuchs-Stationen,  1905-6,  63  :  81. 


216  AGRICULTURAL  ANALYSIS 

phoric  acid  in  basic  slags,  Mach  also  found  that  while  some  forms 
of  the  citric  method  of  direct  precipitation  gave  very  good  results, 
the  molybdate  method,  especially  in  the  case  of  sulfuric  acid  solu- 
tions of  slags,  must  be  regarded,  without  doubt,  as  the  most  re- 
liable. 

189.  Association  and  Other  American  Methods  for  Basic  Slag. 
— The  question  of  adopting  a  method  for  determining  the  avail- 
ability of  phosphoric  acid  in  slag,  has  been  before  the  Association 
of  Official  Agricultural  Chemists  for  the  past  three  years,  and 
quite  a  number  of  reagents  and  processes  have  been  proposed  for 
this  purpose.  The  practical  absence  of  this  form  of  fertilizer 
from  the  American  market  has  prevented  the  manifestation  of 
much  interest  in  the  discussion.  Solubility  has  been  determined 
in  1.09  ammonium  citrate,  in  one  per  cent,  citric  acid,  in  two  per 
cent,  citric  acid,  and  in  all  these  after  preliminary  treatment  with 
water  or  with  five  per  cent,  sugar  solution  followed  by  five  per 
cent,  ammonium  chlorid  solution  as  suggested  by  Macfarlane.88 
The  referee  for  1902  shows  that  the  Wagner  method  indicates 
about  80  per  cent,  of  the  phosphoric  acid  in  slag  as  available  and 
the  ammonium  citrate  method,  30  per  cent.  The  former  is  regarded 
as  too  high,  and  the  latter,  too  low.  He  suggests  that  a  percentage 
be  established  that  may  be  regarded  as  representing  the  amount 
of  availability,  and  a  method  could  then  be  devised  to  give  this 
amount.69  While  no  action  was  taken,  the  sentiment  of  the  asso- 
ciation appeared  to  be  in  favor  of  a  valuation  based  on  the  deter- 
mination of  phosphoric  acid  and  of  fineness  as  is  now  the  usage 
in  the  case  of  raw  bone. 

Hilgard  has  called  attention  to  the  increasing  use  of  phosphatic 

slags  in  California  and  attributes  their  good  effects  to  the  large 

quantity  of  lime  in  the  arid  soils.     This  condition  secures  the 

reversion  of  the  water-soluble  acid   in   superphosphates  within 

the  first  three  or  four  inches  of  the  surface  of  the  soil.  Deep 

plowing  is,  therefore,  necessary  to  bring  the  phosphoric  acid  into 

contact  with  the  lower  roots  of  the  crop.     Such  plowing  would 

also  mix  basic  phosphates  with  the  deeper  layers  of  the  soil,  and 

*  Dirision  of  Chemistry,  Bulletin  62,  1901  :  46. 

69  Bureau  of  Chemistry,  Bulletin  73,  1903  :  16. 


GERMAN  MANUFACTURERS'  METHOD  217 

since  the  slags  are  cheaper  than  the  superphosphates  in  California, 
he  recommends  their  use.  He  is  also  in  accord  with  the  senti- 
ment of  the  association  to  value  these  basic  slags,  at  least  provi- 
sionally, by  their  total  content  in  phosphoric  acid  and  their  degree 
of  fineness.70 

Huston  and  Jones  show  that  the  strength  of  citric  acid,  time 
and  temperature  of  digestion,  all  exert  a  marked  effect  on  the 
amount  of  phosphoric  acid  dissolved  from  slags,  as  does  also  the 
relation  of  quantity  of  material  to  volume  of  solvent.71  It  was 
found  that  even  when  basicity  of  the  slag  was  corrected  the 
reaction  with  citric  acid  was  far  from  complete  in  30  minutes  at 
a  temperature  of  65°.  The  same  conclusion  holds  with  neutral 
ammonium  citrate,  though  here  the  differences  are  not  so  marked. 
The  work  indicates  that  in  a  relatively  short  time  all  the  phos- 
phoric acid  will  be  dissolved,  even  by  dilute  citric  acid  at  any 
temperature,  this  indicating,  further,  that  the  phosphate  of  basic 
slag  has  practically  a  uniform  composition. 

190.  German  Manufacturers'  Method. — In  the  examination 
of  phosphatic  slags,  the  Union  of  German  Fertilizer  Manufac- 
turers determine  total  phosphatic  acid  after  solution,  (a)  in 
hydrochloric  acid,  and  (b)  in  sulfuric  acid.  In  the  hydrochloric 
acid  method  10  grams  of  finely  ground  phosphatic  slag,  which  has 
passed  through  a  two  millimeter  sieve,  are  placed  in  a  flask  of 
one-half  liter  capacity,  80  cubic  centimeters  of  concentrated  hy- 
drochloric acid  added  and  the  mixture  evaporated  on  a  sand-bath 
to  a  sirupy  consistence.  The  mixture  is  dissolved  in  water,  treated 
with  a  few  drops  of  hydrochloric  acid,  and  after  cooling  the  flask 
is  filled  to  the  mark.  In  50  cubic  centimeters  of  the  filtrate,  after 
the  addition  of  100  cubic  centimeters  of  the  ammonia-citric  acid 
solution,  made  up  according  to  the  method  of  Maercker,  namely, 
1500  grams  of  citric  acid,  5000  cubic,  centimeters  of  24  per  cent, 
ammonia  and  water  to  15  liters,  the  phosphoric  acid  is  now  pre- 
cipitated by  25  cubic  centimeters  of  the  ordinary  magnesia  mix- 
ture, stirred  for  one-half  hour  in  a  shaking  apparatus,  and  after 
standing  two  hours,  filtered  and  treated  as  has  already  been  de- 
scribed for  the  estimation  of  phosphoric  acid  soluble  in  water. 

70  Bureau  of  Chemistry,  Bulletin  81,  1904  :  169. 

71  Division  of  Chemistry,  Bulletin  49,  1897  :  68. 


2l8  AGRICULTURAL  ANALYSIS 

In  the  sulfuric  acid  method,  10  grams  of  phosphatic  slag,  pre- 
pared as  above  described,  are  covered  with  a  few  cubic  centi- 
meters of  sulfuric  acid  (one  to  two)  and  well  shaken.  After  the 
addition  of  50  cubic  centimeters  of  concentrated  sulfuric  acid,  the 
mixture  is  heated  at  first  to  boiling  and  afterwards  just  to  the 
boiling  point,  until  the  mass  is  evaporated  to  a  thick  fluid  and  vio- 
lent bumping  begins.  After  cooling,  water  is  gradually  added  to 
the  mark  and  the  phosphoric  acid  determined  either  by  the  citrate 
or  molybdic  acid  method. 

Estimation  of  Citric-Acid-Soluble  Phosphoric  Acid  in  Basic 
Slag. — The  method  of  estimating  the  citric  acid  soluble  phos- 
phoric acid  in  basic  slag  is  that  of  Wagner,  which  has  already 
been  described. 

191.  Estimation  of  Lime. — When  the  lime  is  to  be  determined 
in  basic  slags,  some  difficulty  may  be  experienced  by  reason  of 
danger  of  contamination  of  the  oxalate  precipitate  with  iron  and 
especially  manganese,  which  is  often  present  in  slags. 

Holleman  proposes  to  estimate  the  lime  in  basic  slag  by  mod- 
ification of  the  methods  of  Classen  and  Jones.72  The  manipula- 
tion is  as  follows :  Fifty  cubic  centimeters  of  an  acid  solution 
of  slag,  from  which  the  separated  silica  has  been  removed  by  fil- 
tration, equivalent  to  one  gram  of  substance,  are  evaporated  to  a 
small  volume,  20  cubic  centimeters  of  neutral  ammonium  oxalate 
solution  (one  to  three)  added  to  the  residue  and  heated  on  a 
water  bath,  with  frequent  stirring,  until  the  precipitate  is  pure 
white  and  free  from  lumps.  The  time  required  is  usually  about 
10  minutes.  The  precipitate  is  collected  on  a  filter  and  washed 
with  hot  water  until  the  filtrate  contains  no  oxalic  acid.  The 
precipitated  calcium  oxalate  must  be  snow-white.  The  filter  is 
broken  and  the  calcium  oxalate  washed  through,  first  with  water 
and  finally  with  warm,  dilute  hydrochloric  acid  (one  to  one), 
The  calcium  oxalate  is  dissolved  by  adding  15  cubic  centimeters 
of  concentrated  hydrochloric  acid,  the  solution  evaporated  to  a 
volume  of  about  25  cubic  centimeters,  and  10  cubic  centimeters 
of  dilute  sulfuric  acid  (one  to  five),  and  150  cubic  centimeters 
of  96  per  cent,  alcohol  added.  After  standing  three  hours  or 
72  Chetniker-Zeitung,  1892,  16  :  1471. 


ADULTERATION  OF  PHOSPHATIC  SLAGS  219 

more  the  precipitate  is  separated  by  filtration  and  washed  with  96 
per  cent,  alcohol  until  the  washings  show  no  acid  reaction  with 
methyl  orange.  The  calcium  sulfate  precipitated  is  dried  to  con- 
stant weight.  This  method  gives  a  pure  precipitate  of  calcium 
sulfate,  containing  only  traces  of  manganese. 

192.  Estimation  of  Caustic     Lime. — The     lime     mechanically 
present  in  basic  slags  is  likely  to  be  found  as  oxid  or  hydroxid, 
especiajly  when  the  sample  is  of  recent  manufacture.    In  the  form 
of  oxid  the  lime  may  be  determined  by  solution  in  sugar.    In  this 
process  one  gram  of  the  fine  slag  meal  is  shaken  for  some  time 
with  a  solution  of  sugar,  as  suggested  by  Stone  and  Scheuch.73 
The  dissolved  lime  may  be  titrated  directly  with  standard  hydro- 
chloric acid,  or  the  lime  is  separated  as  oxalate  from  the  hydro- 
chloric acid  solution  by  treatment  of  the  solution  with  ammonium 
oxalate.     The  calcium  oxalate  may  be  determined  by  ignition  in 
the  usual  way  or  volumetrically  by  solution  in  sulfuric  acid  and 
titration  of  the   free  oxalic  acid  with  potassium  permanganate 
solutions.     The  standard  solution  of  permanganate  should  be  of 
such  a  strength  as  to  have  one  cubic  centimeter  equivalent  to 
about  o.oi  gram  of  iron.     The  iron  value  of  the  permanganate 
used  multiplied  by  0.5  will  give  the  quantity  of  calcium  oxid 
found. 

193.  Detection  of  Adulteration  of  Phosphatic  Slags. — The  high 
agricultural  value  of  phosphatic  slags  has  led  to  their  adultera- 
tion and  even  to  the  substitution  of  other  bodies.    Several  patents 
have  also  been  granted  for  the  manufacture  of  artificial  slags  of 
a  value  said  to  be  an  approximation  to  that  of  the  by-products 
of  the  basic  pig  iron  process. 

(i)  Method  of  Blum. — One  of  the  earliest  methods  of  exam- 
ining basic  slag  for  adulterations  is  the  method  of  Blum.7*  This 
method  rests  upon  the  principle  of  the  determination  of  the  car- 
bon dioxid  in  the  sample.  The  basic  phosphatic  slag  is  supposed 
to  contain  no  carbon  dioxid.  This  is  true  only  in  case  it  is 
freshly  prepared.  The  tetrabasic  phosphate,  after  being  kept 
for  some  time,  gradually  absorbs  carbon  dioxid  from  the  air.  As 
high  as  19  per  cent,  of  carbon  dioxid  have  been  found  in  slags 

"  Journal  of  the  American  Chemical  Society,  1894,  16  :  721. 

74  Zeitschrift  fur  analytische  Chemie,  1890, '29  :  408. 


22O  AGRICULTURAL   ANALYSIS 

which  have  been  kept  for  a  long  while.  When  the  slag  has  ab- 
sorbed so  much  of  carbon  dioxid  and  water  from  the  air  as  to 
be  no  longer  profitable  for  market,  it  can  be  restored  to  its  orig- 
inal condition  by  ignition.  Any  great  loss  on  ignition  is  a  ground 
for  suspicion  concerning  the  purity  and  utility  of  a  slag. 

(2)  Method  of  Richters-Forster. — One  of  the  common  adulter- 
ants of  tetrabasic  phosphate  is  aluminum  (Rodonda)  phosphate 
The  method  of  detecting  this  when  mixed  with  the  slag  is  de- 
scribed by  Richters-Forster.75     The  method  depends  on  the  fact 
that  soda-lye  dissolves  the  aluminum  phosphate,  although  it  does 
not  dissolve  any  calcium  phosphoric  acid  from  the  slag.     Two 
grams  of  the  sample  to  be  tested  are  treated  with  10  cubic  centi- 
meters of  soda-lye  of  from  7°  to  8°  B.  in  a  small  vessel,  with 
frequent  shaking,  for  a  few  hours  at  room  temperature.  After 
filtration  the  filtrate  is  made  acid  with  hydrochloric  and  afterwards, 
slightly  alkaline  with  ammonia.    With  pure  basic  slag  there  is  a 
small  trace  of  precipitate  produced,  but  this  is  due  to  a  little  silica, 
which  can  be  dissolved  in  a  slight  excess  of  acetic  acid.      If, 
however,  the  basic  slag  contains  aluminum  phosphate,  a  dense 
jelly-like  precipitate  of  aluminum  phosphate  is  produced. 

(3)  Method  of  Jensch. — Edmund  Jensch  determines  the  tera- 
basic  phosphate  in  slags  by  solution  in  organic  acids,  and  pre- 
fers citric  acid  for  this  purpose.76     This  method  was  also  recom- 
mended by  Blum.77 

It  is  well  known  that  the  tetrabasic  phosphate  in  slags  is  com- 
pletely soluble  in  citric  acid,  while  the  tribasic  phosphate  is  only 
slightly,  if  at  all,  attacked.  The  neutral  ammonium  salts  of  or- 
ganic acids  do  not  at  first  attack  the  tribasic  phosphate  at  all, 
and  they  do  not  completely  dissolve  the  tetrabasic  phosphate. 
The  solution  used  by  Jensch  is  made  as  follows :  Fifty  grams  of 
crystallized  citric  acid  are  dissolved  in  one  liter  of  water.  A 
weaker  acid  dissolves  the  tetrabasic  phosphate  too  slowly  and  a 
stronger  one  attacks  the  tribasic  phosphate  present. 

74  Mitteilungen   der  deutschen   l/andwirtschafts-Gesellschaft,    189091, 
5  :  131. 

Zeitschrift  fur  angewandte  Chetnie,  1890,  S  :  595. 
7'  Zeitschrift  fur  angewandte  Chemie,  1889,  2  :  299. 
"  Zeitschrift  fiir  analytische  Chemie,  1890,  29  :  409. 


ADULTERATION  OF  PHOSPHATIC  SLAGS  221 

Schucht  recommends  the  following  method  of  procedure.78 
One  gram  of  the  slag,  finely  ground,  is  treated  in  a  beaker  glass 
with  about  150  cubic  centimeters  of  Jensch's  citric  acid  solution 
.and  warmed  for  12  hours  in  an  air-bath  at  from  50°  to  70° 
with  frequent  shaking.  Afterwards  it  is  diluted  with  100  cubic 
centimeters  of  water,  boiled  for  one  minute  and  filtered.  The 
filter  is  washed  thoroughly  with  hot  water  and  the  phosphoric 
acid  is  estimated  in  the  filtrate  in  the  usual  way.  With  artificial 
mixtures  of  basic  slags  and  other  phosphates,  the  quantity  of  basic 
slag  can  be  determined  by  the  above  method. 

(4)  Method  of  Wrampelmeyer. — According  to  Wrampelmeyer, 
the  most  convenient  method  for  discovering  the  adulteration  of 
basic  slag  is  the  use  of  the  microscope.79     All  finely  ground  nat- 
ural phosphates  are  light  colored  and  with  a  strong  magnifica- 
tion, appear  as  rounded  masses.  In  basic  slags  the  particles  are 
mostly  black,  but  there  are  often  found  red-colored  fragments 
having  sharp  angles,  which  retract  the  light  in  a  peculiar  way, 
so  that,  with  a  very  little  experience,  they  can  be  recognized  as 
being  distinctive  marks  of  pure  basic  slag. 

In  artificial  mixtures  of  these  two  phosphates,  which  we  have 
made  in  the  laboratory  of  the  Division  of  Chemistry,  we  have  been 
able  to  detect  with  certainty  as  little  as  one  per  cent,  of  added 
mineral  phosphate. 

One  form  of  adulterating  natural  mineral  phosphates  has  been 
mixing  them  with  finely  pulverized  charcoal  or  soot  to  give  them 
the  black  appearance  characteristic  of  the  basic  slags.  This 
form  of  adulteration  is  at  once  disclosed  by  simple  ignition  or  by 
microscopic  examination. 

(5)  Loss  on  Ignition. — If  all  doubts  cannot  be  removed  by  the 
use  of  the  microscope,  the  loss  on  ignition  should  be  estimated. 
Natural  phosphates  all  give  a  high  loss  on  ignition,  ranging  from 
eight  to  24  per  cent.,  while  a  basic  slag  gives  only  a  very  slight 
loss  on  ignition,  especially  when  fresh.     A  basic  slag  which  has 
stood  for  a  long  while  and  absorbed  carbon  dioxid  and  moisture, 
may  give  a  loss  on  ignition  approximating,  in  a  maximum  case, 
the  minimum  loss  on  ignition  from  a  natural  phosphate. 

78  Zeitschrift  fiir  angewandte  Chetnie,  1890,  3  :  594- 

79  Die  landwirtschaftlichen  Versuchs-Stationen,  1894,  43  :  183. 


222  AGRICULTURAL  ANALYSIS 

In  experiments  made  in  the  laboratory  of  the  Division  of  Chem- 
istry in  testing  for  loss  on  ignition,  we  have  uniformly  found 
that  natural  mineral  phosphates  will  lose  from  nearly  one  to  2.5 
times  as  much  on  ignition  as  a  basic  slag  which  has  been  kept 
for  two  years.  A  basic  slag  in  the  laboratory  more  than  two 
years  old  gave,  as  loss  on  ignition,  4.12  per  cent.  Several  sam- 
ples of  finely  ground  Florida  phosphates  gave  the  following  per- 
centages of  loss  on  ignition,  as  compared  with  a  sample  of  slag: 

Odorless  phosphate  (slag),  4.12. 

Florida  phosphates,  8.06,  6.90,  9.58,  6.40,  10.38  and  10.67,  re- 
spectively. 

There  are  some  mineral  phosphates,  however,  which  are  ig- 
nited before  being  sent  to  the  market.  We  have  had  one  such  sam- 
ple in  the  laboratory  from  Florida  which  gave,  on  ignition,  a  loss 
of  only  1.4  per  cent.  In  this  case  it  is  seen  that  the  application  of 
the  process  of  ignition  would  not  discriminate  between  a  basic 
slag  and  a  mineral  phosphate. 

It  may  often  be  of  interest  to  know  what  part  of  the  loss,  on 
ignition,  is  due  to  loosely  held  water  in  form  of  moisture.  In 
such  cases  the  sample  should  first  be  dried  to  constant  weight 
and  then  ignited.  In  the  following  data  are  found  the  results 
obtained  with  samples  treated  as  above  indicated  and  also  ignited 
directly.  Number  one  is  a  basic  slag  two  years  old  and  the  others 
are  Florida  phosphates. 

Heated  to  100°  C.  then  ignited.  Ignited  directly. 

I.oss  at  JyOss  on  Total  I.oss  on 

100°  C.  ignition.  loss.  ignition. 

No.  i  (Slap) 2.57  1.77  4.34  4.12 

No.  2  (Rock) 2.61  5.19  7.80  8.06 

No.  3       "        1.09  5.77  6.86  6.90 

No.  4      "        0.42  9.20  9.62  9.58 

No.  5       "        1.81  4.83  6.64  6.40 

No.  6      "        4.36  6.52  10.88  10.83 

No.  7       "        3.31  7.01  10.32  10.67 

(6)  Presence  of.  Snlfids. — Another  point  noticed  in  the  labora- 
tory of  the  Division  of  Chemistry  is  that  the  basic  slags  uniformly 
contain  sulfids  which  are  decomposed  upon  the  addition  of  an 
acid  with  an  evolution  of  hydrogen  sulfid. 

(7)  Presence  of  Fluorin. — In  applying  the  test  for  fluorin,  it 
has  been  uniformly  found  here,  that  the  mineral  phosphates  respond 


ADULTERATION  OF  PHOSPHATIC  SLAGS  223 

to  the  fluorin  test,  while  the  basic  slags,  on  the  contrary,  respond 
to  the  hydrogen  sulfid  test.  This  test,  however,  was  applied  only 
to  the  few  samples  we  have  had  and  may  not  be  a  uniform 
property. 

The  absence  of  fluorin  might  not  prove  the  absence  of  adul- 
teration, but  its  presence  would,  I  believe,  certainly  prove  the 
fact  of  the  adulteration  in  that  particular  sample. 

The  fluorin  test  is  applied  by  Bottcher  in  the  following  man- 
ner:80 From  10  to  15  grams  of  the  slag  are  placed  in  a  beaker 
10  centimeters  high  and  from  five  to  six  centimeters  in  diam- 
eter, with  15  cubic  centimeters  of  concentrated  sulfuric  acid, 
stirred  with  a  glass  rod,  and  covered  with  a  watch-glass,  on  the 
under  side  of  which  a  drop  of  water  hangs.  If  there  be  formed 
upon  the  drop  of  water  a  white  murky  rim,  it  is  proof  that  a 
mineral  phosphate  containing  fluorin  has  been  added.  After  from 
five  to  10  minutes  you  can  notice  on  the  clean  watch-glass  the 
etching  produced  by  the  hydrofluoric  acid.  According  to  Bottcher 
an  adulteration  of  10  per  cent,  of  raw  phosphate  in  slag  can  be 
detected  by  this  method. 

(8)  Solubility  in  Water. — Solubility  in  water  is  also  a  good 
indication,  natural  phosphates  being  totally  insoluble  in  water, 
while  a  considerable  quantity  of  the  basic  slag  will  be  dissolved 
in  water  on  account  of  the  calcium  oxid  or  hydroxid  which  it 
contains.  If  the  loss  on  ignition  is  low,  and  the  volume-weight 
and  water-solubility  high,  the  analyst  may  be  certain  that  the 
sample  is  a  pure  slag. 

In  comparative  tests  made  in  the  laboratory  of  the  Division  of 
Chemistry  with  a  sample  of  basic  slag  and  seven  samples  of 
Florida  phosphate,  the  percentages  of  material  dissolved  by  water 
and  by  a  five  per  cent,  solution  of  citric  acid  were  found  to  be  as 
follows : 

Water-soluble.  Soluble  in  5  per  cent,  citric  acid 

Per  cent.  Per  cent. 

Basic  slag 0.97  16. 10 

Florida  phosphate o.oi  4. 15 

0.09  4-66 

0.02  3.43 

0.08  3.61 

0.02  3.79 

0.05  4.46 

O.O2  4.24 

99  Chetniker-Zeitung,  1894,  18  :  565. 


224  AGRICULTURAL   ANALYSIS 

From  the  above  data  it  is  seen  that  the  solvent  action  of  water 
especially  would  be  of  value,  inasmuch  as  it  dissolves  only  a  mere 
trace  of  the  mineral  phosphates,  approximating  one  per  cent,  of 
the  amount  dissolved  from  basic  slag.  In  the  case  of  the  citric 
acid  it  is  found  that  the  amount  of  materials  soluble  in  this  sol- 
vent for  basic  slag  is  fully  four  times  as  great  as  for  the  mineral 
phosphates.  Both  of  these  processes,  therefore,  have  considera- 
ble value  for  discriminating  between  the  pure  and  adulterated 
article  of  basic  slag. 

(9)  Specific  Gravity. — The  estimation  of  the  specific  gravity 
is  also  a  good  indication  for  judging  of  the  purity  of  the  slag. 
This  is  best  done  by  weighing  directly  a  given  volume.     Basic 
slag  will  have  a  specific  gravity  of  about  1.9,  while  natural  phos- 
phates will  have  about  1.6. 

(10)  Conclusions. — From  the  above  resume  of  the  standard 
methods  which  are  in  use  for  determining  the  adulteration  of 
basic  slag,  it  is  seen  that  there  are  many  cases  in  which  grave 
doubt  might  exist  even  after  the  careful  application  of  all  the 
methods  mentioned.    If  we  had  only  to  consider  the  adulteration 
of  basic  slag  with  certain  of  the  mineral  phosphates,  that  is,  tri- 
calcium  phosphate,  the  problem  would  be  an  easy  one,  but  when 
we  add  to  this  the  fact  that  iron  and  aluminum  phosphates  are 
employed  in  the  adulteration,  and  that  artificial  slags  may  be  so 
used,  the  question  becomes  more  involved. 

Of  the  single  tests,  examination  with  the  microscope  appears 
to  be  the  most  fruitful. 

In  doubtful  cases,  one  after  another  of  the  methods  should  be 
applied  until  there  is  no  doubt  whatever  of  the  judgment  which 
should  be  rendered. 

DETERMINATION  OF  OTHER  CONSTITUENTS  IN 
NATURAL  PHOSPHATES 

194.  Water  and  Organic  Matters. — The  sample  used  for  deter- 
mining water  and  organic  matters,  according  to  the  practice  of 
Chatard,  should  be  ground  fine  enough  to  leave  no  residue  on 
an  80  mesh  sieve,  and  should  be  thoroughly  mixed  by  passing  it 
three  times  through  a  40  mesh  sieve.81 

81  Transactions  of  the  American  Institute  of  Mining  Engineers,  1892-93, 
21  :  165. 


CARBON    DIOXID  22$ 

Two  grams  are  placed  in  a  tared  platinum  crucible,  which, 
with  its  lid,  is  placed  in  an  air  bath  at  105°  and  heated  for  at 
least  three  hours.  The  lid  is  then  put  on,  and  the  crucible  is 
placed  in  a  desiccator  and  weighed  as  soon  as  cold.  The  loss  in 
weight  is  the  moisture.  The  organic  matter  is  determined  as 
below. 

Wyatt  recommends  that  two  grams  of  the  fine  material  be 
heated  in  ground  watch-glasses,  the  edges  of  which  are  separated 
so  as  to  allow  the  escape  of  the  moisture.82  The  heating  is  con- 
tinued for  three  hours  at  110°,  the  watch-glasses  then  closed 
and  held  by  the  clip,  cooled  in  a  desiccator,  and  weighed.  This 
method  is  excellent  for  very  hygroscopic  bodies,  but  where  quick- 
acting  balances  are  used,  scarcely  necessary  for  a  powdered 
mineral. 

The  residue  from  the  moisture  determination  is  brought  into 
a  platinum  crucible  and  gradually  heated  to  full  redness  over  a 
bunsen,  and  then  ignited  over  the  blast-lamp.  This  operation  is  re- 
peated after  weighing  until  a  constant  weight  is  obtained.  The  loss 
(after  deducting  the  percentage  of  carbon  dioxid  as  found  in 
another  portion)  may  be  taken  as  water  and  organic  matter. 
This  method  is  sufficient  for  all  practical  purposes,  but  when 
minerals  containing  fluorin  are  strongly  ignited,  a  part  of  the 
fluorin  is  expelled;  hence,  if  more  accurate  determinations  are 
required,  the  loss  of  fluorin  must  be  taken  into  account.  It  has 
been  proved  that  a  pure  calcium  fluorid  undergoes  progressive 
decomposition  at  a  bright  red  heat  with  formation  of  lime. 

195.  Carbon  Dioxid. — Many  forms  of  compact  apparatus  have 
been  devised  for  this  estimation,  but  none  of  them  is  more  satis- 
factory than  Knorr's  apparatus,  described  in  Volume  I.  Many 
phosphates  must  be  heated  to  the  boiling  point  with  dilute  acid 
to  effect  complete  decomposition  of  the  carbonates.  The  dis- 
tillation method  described  by  Gooch  is  excellent,  and  when 
once  the  apparatus  is  set  up  its  work  will  be  found  to  be  rapid 
and  satisfactory.83 

Wyatt  regards  the  estimation  of  carbon  dioxid  as  one  of  the 

M  Phosphates  of  America,  4th  Edition,  1892  :  144. 
83  U.  S.  Geological  Survey,  Bulletin  47,  1888  :  16. 


226  AGRICULTURAL  ANALYSIS 

most  important  for  factory  use.  The  carbonates  present  in  a 
sample  indicate  the  loss  of  an  equivalent  amount  of  acid  in  the 
process  of  conversion  into  superphosphate.84 

The  apparatus  employed  for  estimating  carbon  dioxid  may  be 
any  one  of  those  in  ordinary  use  for  this  purpose.  The  principle 
of  the  process  depends  on  the  liberation  of  the  gas  with  a  mineral 
acid,  its  proper  desiccation,  and  subsequent  absorption  by  a  caustic 
alkali,  best  in  solution.  The  methods  described  for  soils  in  Vol- 
ume I  are  generally  applicable  to  this  class  of  materials. 

The  weight  of  the  sample  should  be  regulated  by  the  content 
of  carbonate.  When  this  is  very  high,  from  one  to  two  grams 
will  be  found  sufficient ;  when  low,  a  larger  quantity  must  be  used. 
Hydrochloric  is  preferred  as  the  solvent  acid.  Those  forms  of 
apparatus  which  are  weighed  as  a  whole  and  the  carbon  dioxid 
determined  by  reweighing  after  its  expulsion,  are  not  as  reliable 
as  the  absorption  apparatus  mentioned. 

196.  Soluble  and  Insoluble  Matter. — To  determine  the  insolu- 
ble and  by  difference  the  soluble  and  volatile  contents  of  a  min- 
eral phosphate,  five  grams  of  the  finely  ground  phosphate  are  put 
into  a  beaker,  25  cubic  centimeters  of  nitric  acid  (specific  gravity 
i. 20),  and  12.5  cubic  centimeters  of  hydrochloric  acid  (specific 
gravity  1.12)  are  added.  The  beaker,  covered  with  a  watch- 
glass,  is  placed  upon  the  water  bath  for  30  minutes.  The  con 
tents  of  the  beaker  are  well  stirred  from  time  to  time,  and  at  the 
end  of  the  period  the  beaker  is  removed  from  the  bath,  filled  with 
cold  water,  well  stirred,  and  allowed  to  settle.  The  solution  is 
filtered  into  a  half-liter  flask,  and  the  residue  is  thoroughly 
washed  with  cold  water,  partially  dried,  and  then  ignited  (finish- 
ing with  the  blast-lamp),  and  brought  to  constant  weight.  The 
figures  thus  obtained  will,  however,  be  incorrect,  because  the 
fluorin  liberated  during  the  solution  of  the  phosphates  dissolves 
a  portion  of  the  silica.  Hence  the  results  are  too  low.  Never- 
theless, as  the  same  action  would  occur  in  the  manufacture  of  a 
superphosphate  from  the  same  material,  the  determination  may 
be  considered  as  a  fair  approximation  to  commercial  practice. 
The  ignited  residue  must  be  tested  for  phosphorus  pentoxid. 
84  Phosphates  of  America,  4tb  Edition,  1892  :  145. 


LOSS  OF  SIUCA  AND  FL,UORIN  22/ 

197.  Treatment  of  the  Solution. — The     flask     containing     the 
nitrate  is  filled  to  the  mark  with  cold  water,  and  the  solution 
is  thoroughly  mixed  by  twice  pouring  into  a  dry  beaker  and 
returning  to  the  flask.     Cold  water  is  used  for  washing  the  res- 
idue, since  if  hot  water  be  used,  the  sesquichlorids  are  apt  to 
become  basic  and  insoluble,  and  hence  to  remain  in  the  residue 
and  on  the  filter  paper.    Besides,  as  the  flask  is  to  be  filled  to  the 
mark,  the  contents  must  be  cold  before  any  volumetric  measure- 
ments can  be  made.     The  solution  may  then  be  used  for  the 
general  determination  of  the  dissolved  matters  therein. 

198.  Silica  and  Insoluble  Bodies. — Wyatt  describes  the  follow- 
ing method  for  determining  the  total  insoluble  or  siliceous  matters 
in  a  mineral  phosphate.85     Five  grams  of  the  fine  sample  are 
placed  in  a  porcelain  dish  with  about  30  cubic  centimeters  of 
aqua  regia.     The  dish  is  covered  with  a  funnel,  placed  on  a  sand 
bath,  and,  after  solution  is  complete,  evaporated  to  dryness  with 
care  to  prevent  spluttering.     When  dry,  the  residue  is  moistened 
with  hydrochloric  acid  and  again  dried,  rubbing  meanwhile  to  a 
fine  powder.     The  heat  of  the  bath  is  then  increased  to   125° 
and  maintained  at  this  temperature  for  about  10  minutes.    When 
cool,  the  residue  is  treated  with  50  cubic  centimeters  of  hydro- 
chloric acid  for  15  minutes.     The  acid  is  then  diluted  and  fil- 
tered on  a  gooch,  which  is  washed  with  hot  water  until  the  filtrate 
amounts  to  a  quarter  of  a  liter.     The   residue  in  the  crucible 
is  dried,   ignited  and  weighed.     Unless  the  solution  be  subse- 
quently boiled  with  nitric  acid,  all  the  phosphoric  acid  may  not 
be  retained  in  the  ortho  form. 

199.  Loss  of  Silica  and  Fluorin. — It    is    difficult    to    estimate 
the  total  silica  by  the  ordinary  methods  of  mineral  analysis.    This 
is  due  to  the  fact  that  in  an  acid  solution  of  a  substance  con- 
taining silicates  and  fluorids  the  whole  of  the  silica  or  the  fluorin, 
as  the  case  may  be,  may  escape  as  silicofluorid  on  evaporation. 
Again,  it  is  not  easy  to  decompose  calcium  phosphate  by  fusing 
with  sodium  carbonate.     If  an  attempt  be  made  to  do  this,  how- 
ever, the  process  should  be  conducted  as  follows :    A  portion  of 
the  sample  is  ground  to  an  impalpable  powder  in  an  agate  mor- 
tar.    From  one  to  two  grams  of  the  substance  are  mixed  with 

85  Phosphates  of  America,  4th  Edition,  1892  :  147. 


228  AGRICULTURAL  ANALYSIS 

five  times  its  weight  of  sodium  carbonate  and  fused  with  the 
precautions  given  in  standard  works  on  quantitative  analysis. 
The  fused  mass  is  digested  in  water,  boiled,  and  filtered,  and  the 
residue  washed  first  with  boiling  water  and  afterwards  with  am- 
monium carbonate.  The  filtrate  contains  all  the  fluorin  as  sodium 
fluorid,  and,  in  addition  to  this,  sodium  carbonate,  silicate  and 
aluminate.  The  filtrate  is  mixed  with  ammonium  carbonate  and 
heated  for  some  time,  replacing  the  ammonium  carbonate  which 
evaporates.  The  silicic  acid  and  aluminum  hydroxid  which  are 
formed,  are  separated  by  filtration  and  washed  with  ammonium 
carbonate.  To  separate  the  last  portions  of  silica  from  the  fil- 
trate, add  a  solution  of  zinc  oxid  in  ammonia.  Evaporate  until 
no  more  ammonia  escapes  and  separate  by  filtration  the  zinc 
silicate  and  oxid.  Determine  the  silica  in  this  precipitate  by  dis- 
solving in  nitric  acid,  evaporating  to  dryness,  taking  up  with 
nitric  acid  and  separating  the  undissolved  silica  by  filtration. 
In  the  alkaline  nitrate  the  fluorin  may  be  estimated  by  the  usual 
method  as  calcium  salt. 

200.  Estimation  of  Lime. — The  following  is  the  Glaser-Jones 
method,  as  practiced  by  Chatard  in  the  Geological  Survey:88 
One  hundred  cubic  centimeters  of  the  solution  (containing  one 
gram  of  the  original  substance)  are  evaporated  in  a  beaker  to 
about  50  cubic  centimeters ;  10  cubic  centimeters  of  dilute  sul- 
furic  acid  (one  to  five)  are  added;  and  the  evaporation  is  con- 
tinued on  the  water  bath  until  a  considerable  crop  of  crystals 
of  gypsum  has  formed.  The  solution  is  allowed  to  cool,  when 
it  generally  becomes  pasty,  owing  to  the  separation  of  additional 
gypsum,  and  150  cubic  centimeters  of  95  per  cent,  alcohol  are 
slowly  added,  with  continual  stirring,  and  the  whole  is  allowed 
to  stand  for  three  hours,  being  stirred  from  time  to  time,  filtered, 
with  the  aid  of  a  filter-pump,  into  a  distillation  flask,  and  the 
crystalline  precipitate  washed  with  95  per  cent,  alcohol.  The 
filter,  with  the  precipitate,  is  removed  from  the  funnel  and  in- 
verted into  a  platinum  crucible,  so  that,  by  squeezing  the  point 
of  the  filter,  the  precipitate  is  made  to  fall  into  the  crucible,  and 
the  paper  can  be  pressed  down  smoothly  upon  it.  On  gentle 

M  Transactions  of  the  American  Institute  of  Mining  Engineers,  1892-93, 
21  :  168. 


LIME  METHOD  OF  IMMENDORFF  229 

heating  of  the  crucible,  the  remaining  alcohol  burns  off ;  and  when 
the  paper  has  been  completely  destroyed,  the  heat  is  raised  to  the 
full  power  of  a  bunsen  for  about  five  minutes.  After  cooling  in 
a  desiccator  the  crucible  containing  the  calcium  sulfate  is  weighed. 
The  filtration  may  also  be  accomplished  on  asbestos  felt. 

201.  The    Ammonium    Oxalate    Method. — This     method     has 
been  extensively  used  in  this  country  in  commercial  work,  and  is 
carried  out  as  described  by  Wyatt.87     The  total  filtrates  from  the 
iron  and  alumina  precipitates,  secured  as  described  in  paragraph 
196,  are  well  mixed  and  concentrated  to  a  volume  of  about  100 
cubic  centimeters.     There  are  added  about  20  cubic  centimeters 
of  a  saturated  solution  of  ammonium  oxalate,  and,  after  stirring, 
the  mixture  is  allowed  to  cool  and  remain  at  rest  for  six  hours. 
The  supernatant  liquid  is  poured  through  a  filter,  the  residue 
washed  three  times  by  decantation  with  hot  water  and  brought 
upon  the  filter.     The  beaker  and  precipitate  are  washed  at  least 
three  times.    The  precipitate  is  dried  and  ignited  at  low  redness 
for  10  minutes.     The  temperature  is  then  raised  by  a  blast  and 
the  ignition  continued  for  five  minutes  longer,  or  until  the  lime 
is  obtained  as  oxid.     The  precipitate  is  likely  to  contain  some 
magnesia.     The  magnesia  is  estimated  in  the  filtrates  from  the 
lime  determination  by  first  mixing  them  and  concentrating  to 
loo  cubic  centimeters,  which,  after  cooling,  are  made  strongly 
alkaline  with  ammonia.     After  allowing  to  stand  for  12  hours, 
the  ammonium  magnesium  phosphate  is  collected  and  reduced 
to  magnesium  pyrophosphate   by   the  usual   processes.     If  one 
gram  of  the  original  material  has  been  used,  the  pyrophosphate 
obtained,  multiplied  by  0.36,  will  give  the  weight  of  magnesia 
contained  therein. 

202.  Lime    Method    of    Immendorff. — The     tedious     processes 
required  to  determine  the  lime  in  the  presence  of  iron,  alumina, 
and  large  quantities  of  phosphoric  acid  are  well  known  to  ana- 
lysts.    Immendorff  has  published  a  method,  accompanied  by  ex- 
perimental data,  based  on  the   comparative  insolubility  of  cal- 
cium oxalate  in  a  very  dilute  solution  of  hydrochloric  acid.     He 
has  shown  in  the  data  given  that  the  lime  is  all  precipitated  in 
the  conditions  named  and  that  the  precipitate,  when  properly  pre- 

87  Phosphates  of  America,  4th  Edition,  1892  :  153. 


230  AGRICULTURAL  ANALYSIS 

pared,  is  not  contaminated  with  weighable  amounts  of  the  other 
substances  found  in  the  original  solution.88  The  ease  with  which 
oxalic  acid  can  be  determined  volumetrically  with  potassium  per- 
manganate solution  aids  greatly  in  the  time-saving  advantages 
of  the  process. 

In  a  hydrochloric  acid  solution  of  a  mineral  phosphate  an 
aliquot  part  of  the  filtrate  representing  about  250  milligrams  of 
calcium  oxid,  usually  about  100  cubic  centimeters,  is  used  for 
the  analysis.  Ammonia  is  added  in  slight  excess  and  then  the 
acid  reaction  restored  with  hydrochloric  until  shown  plainly  by 
litmus.  The  solution  is  then  heated  and  the  lime  thrown  down 
by  adding  a  solution  of  ammonium  oxalate  in  excess.  In  order 
to  secure  a  greater  dilution  of  the  hydrochloric  acid  after  the 
precipitation  has  been  made,  water  is  added  until  the  volume  is 
half  a  liter.  Before  filtering,  the  whole  is  cooled  to  room  tem- 
perature. The  precipitate  is  washed  first  with  cold  and  after- 
wards with  warm  water.  The  well  washed  precipitate  is  dis- 
solved in  hot  dilute  sulfuric  acid  and  the  solution,  while  hot, 
titrated  with  a  standard  solution  of  potassium  permanganate  set 
by  a  solution  of  ammonio-ferrous  sulfate. 

If  one  cubic  centimeter  of  the  permanganate  represent  0.007 
gram  of  iron  it  will  correspond  almost  exactly  to  0.0035  gram  of 
calcium  oxid.  The  presence  of  iron  in  the  original  solution  does 
not  seem  to  affect  the  results. 

Example. — Sample  of  mineral  phosphate,  five  grams  in  half  a 
liter.  Strength  of  potassium  permanganate,  one  cubic  centimeter, 
equivalent  to  0.00697  gram  of  iron  and  to  0.003484  gram  of 
calcium  oxid. 

Twenty-five  cubic  centimeters  of  the  solution,  representing  one 
quarter  of  a  gram,  in  which  the  lime  was  precipitated  as  above 
described,  required  38.4  cubic  centimeters  of  the  potassium  per- 
manganate to  saturate  the  oxalic  acid.  Then  38.4X0.003484= 
0.133786  gram,  or  53.51  per  cent,  of  calcium  oxid.  The  method 
is  also  applicable  to  basic  slags. 

203.  Estimation  of  Iron  and  Alumina  in  Mineral  Phosphates. 
—When  mineral  phosphates  are  to  be  used  for  the  manufacture 
"Die  land wirtschaftlichen  Versuchs-Stationen,  1887,  34  :  379. 


THE  ACETATE  METHOD  231 

of  superphosphates  by  treatment  with  sulfuric  acid  their  content 
of  iron  and  alumina  becomes  a  matter  of  importance.  By  reason 
of  the  poor  drying  qualities  of  the  sulfates  of  these  bases  their 
presence  in  any  considerable  excess  of  a  few  per  cent,  becomes 
exceedingly  objectionable.  The  quantity  of  sulfuric  acid  re- 
quired for  the  formation  of  the  sulfates  is  also  a  matter  of 
economic  importance.  The  accurate  estimation  of  these  ingre- 
dients is  not  only  then  a  matter  of  scientific  interest,  but  one  of 
great  commercial  significance  to  the  manufacturer. 

The  conventional  methods  so  long  in  use  depending  on  the 
precipitation  of  the  iron  and  alumina  as  phosphates  in  the  pres- 
ence of  acetic  acid  have  been  proved  to  be  somewhat  unreliable. 
Not  only  does  the  acetic  acid  fail  to  prevent  the  precipitation  of 
some  of  the  lime,  but  it  also  dissolves  more  or  less  of  the  iron 
and  aluminum  phosphates.  The  solution  of  the  precipitate  and 
its  reprecipitation  by  the  addition  of  ammonia,  may  free  the  sec- 
ond precipitate  from  lime,  but  it  increases  the  error  due  to  the 
solubility  of  the  aluminum  salt.  The  methods  recently  introduced 
for  the  estimation  of  iron  and  alumina  in  presence  of  excess  of 
lime  and  phosphoric  acid  are  not  entirely  satisfactory,  but  are  the 
best  which  can  now  be  offered. 

204.  The  Acetate  Method. — The  principal  of  this  process  is 
based  on  the  fact  that  in  a  solution  containing  iron,  alumina, 
lime  and  phosphoric  acid,  the  iron  and  aluminum  phosphates  can 
be  thrown  down  in  a  slightly  acid  solution  by  ammonium  ace- 
tate while  the  calcium  phosphate  remains  in  solution.  The  acidity 
h;  the  older  methods  is  due  to  acetic  and  can  be  secured  by  making 
the  solution  slightly  alkaline  with  ammonia  and  adding  acetic  to 
slight  acidity.  One  of  the  methods  of  conducting  the  operation 
is  that  of  C.  Glaser.89  This  modification  of  the  older  processes  is 
based  on  the  assumption  that  at  70°  the  iron  and  aluminum  phos- 
phate is  quantitatively  precipitated  by  ammonium  acetate  in  a 
dilute  solution  containing  no  free  chlorin  and  that  the  mixed 
precipitate  of  iron  and  aluminum  phosphates  obtained  at  this 
temperature  is  free  of  lime.  The  operation  is  conducted  in  the 
following  manner: 

The  hydrochloric  acid  solution  of  the  phosphate  must  contain 
M  Zeitschrift  fur  analytische  Chemie,  1892,  31  :  383. 


232  AGRICULTURAL  ANALYSIS 

no  free  chlorin  and  is  treated  with  a  few  drops  of  methyl  orange 
solution.  Ammonia  is  added  until  nearly  neutral,  but  the  acid 
reaction  is  retained,  as  shown  by  the  indicator.  A  few  cubic  cen- 
timeters of  ammonium  acetate  are  added,  which  produce  a  yellow 
coloration  of  the  liquid  and  also  a  complete  precipitation  of  the 
iron  and  aluminum  phosphates  when  warmed  to  70°.  At  this 
temperature  the  precipitation  of  any  calcium  phosphate  is  avoided. 
A  small  quantity  of  the  lime  may  be  carried  down  mechanically 
and  therefore  the  precipitate  should  be  dissolved  in  hydrochloric 
acid  and  the  precipitation  again  made  as  above  after  the  addi- 
tion of  some  sodium  phosphate.  If  the  original  solution  contains 
any  free  chlorin,  as  may  be  the  case  when  aqua  regia  is  employed 
as  solvent,  before  beginning  the  separation,  ammonia  should  be 
added  in  slight  excess  and  the  acidity  restored  by  hydrochloric 
after  adding  the  indicator.  In  washing  the  precipitates,  water  of 
not  over  70°  must  be  used.  As  has  been  shown  by  Hess  in  the 
work  cited  in  the  next  paragraph,  the  statement  that  the  precipi- 
tates obtained  as  above  are  free  of  lime  has  not  been  proved  to 
be  strictly  correct.  The  process,  however,  is  a  distinct  improve- 
ment over  the  older  methods  and  forms  the  basis  of  the  amended 
process  given  below,  which  appears  to  be  sufficiently  accurate  to 
entitle  the  acetate  method  to  favorable  consideration. 

205.  Method  of  Hess. — Hess  has  made  an  investigation  of  the 
standard  methods  of  determining  iron  and  aluminum  oxids  in  the 
presence  of  phosphoric  acid  and  has  shown  that  the  assumption, 
that  the  composition  of  the  precipitate  is  represented  by  the  form- 
ula Al2(PO4)2+Fe2(PO4)2,  is  erroneous.90 

In  the  washing  of  the  precipitated  iron  and  aluminum  phos- 
phates, there  is  a  progressive  decomposition  of  the  compound 
with  the  production  of  the  basic  salt.  The  composition  of  the 
precipitate  at  the  end  is  dependent  chiefly  upon  the  way  in 
which  the  washing  takes  place.  It  is  quite  difficult  to  always 
secure  a  washing  in  exactly  the  same  way,  and  the  final  composi- 
tion of  the  precipitate  varies  with  almost  every  determination. 
It  is  not,  therefore,  an  accurate  proceeding  to  take  half  the 
weight  of  the  precipitate  as  phosphoric  acid  or  as  iron  oxid  and 
90  Zeitschrift  fur  angewandte  Chemie,  1894,  7  :  679,  701. 


METHOD  OF    HESS  233 

alumina.  In  every  case  it  is  necessary  to  dissolve  the  precipi- 
tate and  determine  the  phosphoric  acid  in  the  regular  way. 
.Hess  proposes  the  following  method  for  carrying  out  the  acetate 
process  of  separation: 

The  mineral  phosphate  should  be  dissolved  in  hydrochloric 
acid  and  the  solution  made  up  to  such  a  volume  as  shall  contain 
in  each  50  cubic  centimeters  one  gram  of  the  original  sub- 
stance. This  quantity  of  the  solution  is  diluted  with  two  or 
three  times  its  volume  of  water  to  which  a  drop  of  methyl  orange 
solution  ( 1:100)  is  added,  and  ammonia  added  with  constant 
stirring  until  the  solution  is  just  colored  and  still  reacts  slightly 
acid.  Without  taking  any  account  of  the  precipitate  which  is 
produced  by  this  approximate  neutralization  of  the  solution,  there 
are  added  50  cubic  centimeters  of  acid  ammonium  acetate  which, 
in  one  liter,  contains  250  grams  of  commercial  ammonium  acetate. 
The  acidity  of  the  solution  is  due  to  an  excess  of  acetic  hi  the 
commercial  salt.  The  temperature  is  carried  to  70°  and  the  pre- 
cipitate produced  immediately  separated  by  filtration,  washed 
four  times  with  water  below  70°,  and  again  dissolved  in  dilute 
hydrochloric  acid.  The  solution  is  mixed  with  10  cubic  centi- 
meters of  a  10  per  cent,  ammonium  phosphate  solution  and  again 
almost  neutralized  as  described  above,  and  25  cubic  centimeters 
of  the  ammonium  acetate  solution  added  and  warmed  to  70°. 

The  precipitate  obtained  is  once  more  dissolved  and  precipita- 
ted as  above  described,  and  is  then  collected  upon  a  filter,  washed 
ignited  and  weighed.  The  residue  after  ignition  is  dissolved  in 
the  crucible  by  heating  with  a  little  concentrated  hydrochloric 
acid,  and  washed  into  a  beaker.  Any  silicic  acid  present  is  sepa- 
rated by  filtration,  ignited,  weighed,  and  subtracted  from  the 
total  weight  of  the  precipitate.  To  the  filtrate  is  added  ammonia 
to  diminish  the  acidity,  but  not  sufficient  to  produce  a  precipitate, 
and  the  clear  solution  is  mixed  with  30  cubic  centimeters  of  the 
ordinary  ammoniacal  citrate  solution  and  15  cubic  centimeters  of 
magnesium  mixture,  and  the  precipitation  of  the  ammonium  mag- 
nesium phosphate  hastened  by  stirring  with  a  glass  rod. 

It  is  advisable  to  make  the  filtrate  from  the  third  precipitation 
slightly  ammoniacal  and  to  boil  it  for  a  long  time.  If  the  opera- 


234  AGRICULTURAL  ANALYSIS 

lion  has  been  carried  on  correctly,  there  occurs  only  a  slight  pre- 
cipitate of  Ca3P2O8  amounting  only  to  a  few  milligrams.  In 
some  cases  it  may  be  necessary  to  dissolve  the  precipitate  and 
reprecipitate  the  iron  and  aluminum  phosphates  a  fourth  time. 

The  whole  time  required  for  the  triple  precipitation,  according 
to  Hess,  if  all  the  operations  be  properly  conducted,  is  from 
three  to  four  hours.  It  is  therefore  possible  by  this  variation  of 
the  acetate  method  to  secure  a  determination  of  the  iron  and 
alumina  as  phosphates  in  the  same  time  which  is  occupied  by 
the  Glaser-Jones  method,  when  the  separation  of  lime  is  taken 
into  account. 

If  the  solution  of  the  mineral  phosphate  employed  contains  any 
notable  quantity  of  organic  material,  it  must  be  destroyed  by 
boiling  with  bromin  or  some  other  oxidizing  agent,  before  the 
precipitation  by  the  acetate  method  is  commenced. 

The  presence  of  silicic  acid  need  not  be  taken  into  special  con- 
sideration since  this  can  be  detected  and  determined  in  the  phos- 
phate precipitates  after  they  have  been  ignited  and  weighed. 
The  determinations  of  the  phosphoric  acid  were  made  by  direct 
precipitation  with  ammonium  in  the  presence  of  citrate;  they 
agreed  perfectly  with  the  previous  precipitations  with  molybdic 
solution. 

206.  Method  of  Eugen  Glaser. — The  principle  on  which  this 
method  rests,  depends  on  the  preliminary  removal  of  the  lime  by 
conversion  into  calcium  sulfate  and  its  precipitation  in  the  presence 
of  strong  alcohol.91  This  process  does  not  require  the  use  of 
acetic  acid  which  in  the  old  method  dissolved  more  or  less  of  the 
aluminum  phosphate,  thus  introducing  errors  of  considerable 
magnitude  in  those  cases  where  the  mineral  phosphates  contained 
notable  quantities  of  alumina.  It  is  conducted  as  follows : 

Five  grams  of  the  phosphate  are  dissolved  in  a  mixture  of 
25  cubic  centimeters  of  nitric  acid  of  1.2  specific  gravity  and 
about  12.5  cubic  centimeters  of  hydrochloric  acid  of  1.12  specific 
gravity,  made  up  to  a  volume  of  half  a  liter,  and  filtered.  One 
hundred  cubic  centimeters  of  the  filtrate,  equivalent  to  one  gram 
of  the  substance,  are  placed  in  a  quarter-liter  flask  and  25  cubic 
91  Zeitschrift  fur  angewandte  Chemie,  1889,  2  :  636. 


DIFFICULTIES  OF  THE  GLASER-ALCOHOL  METHOD  235 

centimeters  of  sulfuric  acid  of  1.84  specific  gravity  added.  The 
flask  is  allowed  to  stand  for  about  five  minutes  and  meanwhile 
shaken  a  few  times.  About  100  cubic  centimeters  of  95  per  cent, 
alcohol  are  added  and  then  the  flask  is  filled  with  alcohol  to  the 
mark  and  well  shaken.  A  certain  degree  of  concentration  takes 
place,  and  this  is  compensated  for  by  lifting  the  stopper  and  filling 
.again  with  alcohol  to  the  mark  and  shaking  a  second  time.  After 
allowing  to  stand  for  half  an  hour  the  contents  of  the  flask  are  fil- 
tered, and  loo  cubic  centimeters  of  the  filtrate,  equal  to  four-tenths 
gram  of  the  substance,  evaporated  in  a  platinum  dish  until  the 
alcohol  is  driven  off.  The  alcohol-free  residue  is  heated  to  boil- 
ing in  a  beaker  with  about  50  cubic  centimeters  of  water.  Am- 
monia is  added  to  alkaline  reaction,  but  in  order  to  avoid  strong 
effervescence  it  is  not  added  during  the  boiling.  The  excess  of 
ammonia  is  evaporated,  the  flask  allowed  to  cool,  the  contents 
filtered,  precipitate  and  filter  washed  with  warm  water,  dried, 
ignited  and  the  phosphates  of  iron  and  alumina  weighed.  Half 
of  the  weight  of  the  precipitate  represents  the  weight  of  Fe2O3 
-)-Al2O3.  The  estimation,  as  before  indicated,  should  be  carried 
on  without  delay,  the  whole  time  required  not  exceeding  from 
one  and  a  half  to  two  hours. 

207.  Difficulties  of  the  Glaser-Alcohol  Method. — The  objections 
on  the  part  of  English  chemists  to  the  method  of  freeing  dis- 
solved phosphate  from  lime  by  means  of  alcohol  preparatory  to 
the  separation  of  iron  and  alumina  are  as  follows  :92 

1.  To  working  upon  a  solution  representing  as  little  as  0.4 
gram  of  phosphate. 

2.  To  employing  nitro-hydrochloric  acid  as  the  solvent  for  the 
raw  phosphate    and    consequently  to  including  in  the  oxids    of 
iron  and  alumina  any  iron  previously  present  as  pyrite. 

3.  To  the  plan  of  dividing  the  phosphates  of  iron  and  alumina 
found  by  two  to  obtain  the  oxids  of  iron  and  alumina,  instead  of 
determining  the  phosphoric  acid  in  the  precipitates  and  deducting 
its  weight  from  the  total. 

4.  Should  the  phosphate  under  examination  contain  magnesia, 
the  phosphates  of  iron  and  alumina  obtained  in  the  foregoing 

91  Shepherd,  Chemical  News,  1891,  63  :  251. 


236  AGRICULTURAL  ANALYSIS 

process  must  be  freed  from  this  impurity  by.  removing  the  precipi- 
tate from  the  filter,  boiling  with  water  and  a  little  nitrate  of  am- 
monia and  repeating  this  treatment,  if  after  the  first  application 
of  it,  the  filtrate  still  shows  the  presence  of  magnesia. 

208.  Jones'  Variation. — The  method  of  E.  Glaser  described 
above,  has  been  found  by  Jones  to  be  inaccurate  on  account  of 
the  alcohol  not  being  added  in  sufficient  quantity  in  the  pre- 
cipitation of  calcium  sulfate  and  for  the  additional  reason  that  the 
amount  of  sulfuric  acid  added  is  more  than  is  actually  necessary.83 
A  further  objection  to  the  method  is  found  in  the  small  quantity 
of  the  original  material,  viz.,  0.4  gram,  which  gives  only  a  small 
precipitate  of  iron  and  alumina,  especially  in  those  cases  where 
the  samples  contain  only  small  quantities  of  these  substances. 
Jones  modifies  the  method  as  follows :  Ten  grams  of  the  material 
are  dissolved  in  nitro-hydrochloric  acid  and  the  solution  made  up 
to  500  cubic  centimeters  and  filtered.  Fifty  cubic  centimeters  of 
this  solution,  representing  one  gram,  are  evaporated  to  25  cubic 
centimeters  and,  while  still  hot,  10  cubic  centimeters  of  dilute 
sulfuric  acid  (one  to  five)  added.  The  mixture  is  well  stirred 
and  150  cubic  centimeters  of  95  per  cent,  alcohol  added  and, 
after  stirring,  the  solution  is  allowed  to  stand  three  hours.  The 
calcium  sulfate  is  collected  on  a  filter,  washed  with  alcohol,  and 
the  filtrate  and  washings  collected  in  an  erlenmeyer.  The  wash- 
ing is  completed  when  the  last  10  drops,  after  dilution  with  an 
equal  volume  of  water,  are  not  reddened  with  a  drop  of  methyl 
orange.  The  filtration  is  conveniently  hastened  by  a  moderate 
vacuum. 

The  moist  calcium  sulfate  is  transferred  to  a  platinum  cruci- 
ble, the  filter  placed  on  it,  the  alcohol  burned  off,  the  filter  inciner- 
ated, and  the  calcium  sulfate  ignited  and  weighed.  The  precipi- 
tate is  not  sufficiently  hygroscopic  to  offer  any  difficulties  to  con- 
ducting the  operations  in  an  open  dish.  The  contents  of  the  flask 
are  heated  to  expel  the  alcohol,  which  is  contaminated  with  hydro- 
chloric or  nitric  acid  and  can  not  be  used  again  until  distilled  over 
an  alkali.  The  residue  is  washed  into  a  beaker,  made  slightly 
alkaline  with  ammonia,  and  again  heated  till  all  the  ammonia  is 

n  Zeitschrift  fur  angewandte  Chemie,  1891,  4  :  3. 


IRON  AND  ALUMINA  IN   PHOSPHATES  237 

driven  off.  This  treatment  is  necessary  to  prevent  the  iron  phos- 
phate precipitate  from  being  contaminated  with  magnesia.  The 
precipitate  is  collected  on  a  filter,  washed  four  times  with  hot 
water,  or  water  containing  neutral  ammonium  nitrate,  dried, 
ignited,  and  weighed.  One-half  of  the  weight  of  the  precipitate 
represents  the  weight  of  the  ferric  and  aluminic  oxids.  The 
magnesia  is  thrown  out  of  the  filtrate  by  saturation  with  ammonia 
and  allowing  to  stand  12  hours.  The  phosphoric  acid,  alkalies 
and  sulfuric  acid  are  determined  in  the  original  sample  by  the 
usual  methods.  Jones'  variation  of  the  E.  Glaser  method  has 
been  generally  approved  by  experience  and  is  to  be  recommended 
in  general  in  place  of  the  original  process.94 

209.  Estimation  of  Iron  and  Alumina  in  Phosphates  by  Crispo's 
Method. — The  phosphate  of  ferric  iron  is  subject  to  a  .slight  de- 
composition in  presence  of  both  hot  and  cold  water  with  a  ten- 
dency to  the  production  of  basic  compounds.  It  is  soluble  to  a 
slight  extent  in  hot  and  cold  acetic  acid,  almost  insoluble  in  am- 
monium acetate,  and  quite  insoluble  in  ammonium  chlorid  and 
nitrate.  Aluminum  phosphate  is  likewise  soluble,  to  a  slight  de- 
gree, in  acetic  acid  and  ammonium  acetate,  and  insoluble  in  am- 
monium chlorid  and  nitrate.  The  method  of  Crispo,  as  practiced 
in  the  laboratory  at  Antwerp,  for  the  separation  of  iron  and  alu- 
mina in  phosphates  is  based  on  the  above  properties.95  Five  grams 
of  the  mineral  phosphate  are  dissolved  in  500  cubic  centimeters 
of  aqua  regia,  containing  40  cubic  centimeters  of  hydrochloric 
acid  of  i.io,  and  10  of  nitric  acid  of  1.20  specific  gravity.  To  50 
cubic  centimeters  of  the  filtered  solution  are  added  two  of 
ammonia  (0.96)  and  50  of  a  half-saturated  solution  of  ammo- 
nium chlorid,  and  the  whole  boiled.  The  liquid  should  remain 
clear,  but  if  it  becomes  cloudy  add  a  little  dilute  nitric  acid,  drop 
by  drop,  until  the  turbidity  is  removed,  and  then  10  cubic  cen- 
timeters of  a  saturated  solution  of  ammonium  acetate,  boil  for 
three  minutes,  cool,  and  filter.  The  precipitate  is  washed  twice 
with  a  10  per  cent,  solution  of  ammonium  chlorid  and  redis- 
solved  with  two  cubic  centimeters  of  nitric  acid,  and  the  filter 

94  von  Griiber,  Zeitschrift  fur  analytische  Chemie,  1891,  30  :  206. 

95  First  International  Congress  of    Applied  Chemistry,  Brussels,   1894, 
Proceedings  :  20. 


238  AGRICULTURAL  ANALYSIS 

washed  with  hot  water.  The  phosphoric  acid  is  separated  by 
40  cubic  centimeters  of  molybdate  solution,  and  the  precipi- 
tate washed  three  or  four  times  with  a  one  per  cent,  nitric  acid 
solution. 

To  the  filtrate  are  added  50  cubic  centimeters  of  a  half- 
saturated  ammonium  chlorid  solution,  ammonia  is  added  in 
slight  excess  to  produce  precipitation  and  the  mixture  boiled  for 
a  few  minutes.  After  filtering,  the  precipitate  is  washed  with  hot 
water  three  or  four  times,  dissolved  in  two  cubic  centimeters  of 
nitric  acid,  and  the  filter  washed  with  hot  water.  Again,  50 
cubic  centimeters  of  half-saturated  ammonium  chlorid  solution 
are  added  and  the  precipitate  thrown  down  once  more  by  ammo- 
nia in  slight  excess.  The  precipitate  is  washed  with  hot  water 
and  finally  ignited  and  weighed  as  iron  and  aluminum  oxids. 

According  to  Crispo,  the  original  Glaser  method,  with  its 
various  modifications,  is  not  to  be  considered  reliable,  and  the 
choice  lies  between  the  molybdate  method  as  usually  practiced, 
and  his  own  for  the  accurate  estimation  of  iron  and  alumina. 
Manganese  disturbs  the  accuracy  of  the  results  unless  the  direc- 
tions given  are  carefully  followed.  Manganese  phosphate  is 
soluble  at  all  temperatures  below  50.  If  then  the  mixture  of 
the  phosphates  be  allowed  to  cool  before  filtering,  the  iron  and 
aluminum  salts  are  not  contaminated  with  manganese.  This 
method  of  Crispo  is  somewhat  tedious,  but  it  is  claimed  that  these 
variations  render  it  exact  in  respect  of  the  determination  of  iron 
and  alumina. 

210.  Variation  of  the  Alcohol  Method. — Chatard  conducts  the 
Glaser-Jones  process  as  follows  :96  The  distillation  flask  contain- 
ing the  alcoholic  filtrate  is  connected  with  its  condenser  and 
heated  on  a  water  bath  until  no  more  alcohol  comes  over.  This 
distillate,  if  mixed  with  a  little  sodium  carbonate  and  redistilled 
over  quicklime,  can  be  used  over  and  over  again,  so  that  the  ex- 
pense for  alcohol  is  really  very  slight,  while  in  the  use  of  the 
Glaser  method,  with  its  large  amount  of  sulfuric  acid,  all  the 
alcohol  is  lost. 

When   the   distillation   is   ended    the    residue    in   the   flask   is 

"Transactions  of  the  American  Institute  of  Mining  Engineers,  1892-93, 
21  :  169. 


VARIATION  OF  MARIONI  AND  TASSEXU  239 

washed  into  a  platinum  dish  and  evaporated  to  a  small  bulk  on 
the  water  bath.  The  dark  brown  color  produced  is  due  to  the 
presence  of  organic  matter  and  this  must  be  destroyed,  as  it  pre- 
vents the  complete  precipitation  of  the  phosphate  in  the  subse- 
quent operation. 

The  organic  matter  is  best  destroyed  by  removing  the  dish 
from  the  bath,  adding  a  small  quantity  of  pure  sodium  nitrate, 
and  heating  very  carefully  over  the  naked  flame,  keeping  the 
dish  well  covered  with  a  watch-glass  to  avoid  spattering.  The 
mass  fuses  to  a  colorless,  viscous  liquid,  becoming  glassy  when 
cooled  and  is  readily  soluble  in  a  hot,  very  dilute  solution  of 
nitric  acid.  The  solution  transferred  to  a  beaker  is  made  dis- 
tinctly alkaline  with  ammonia  and  carefully  neutralized  with 
acetic  acid,  diluted  with  hot  water,  boiled,  and  the  precipitate  of 
iron  and  alumina  phosphates  allowed  to  settle,  after  which  it  is 
separated  by  filtration. 

After  the  precipitate  has  been  completely  transferred  to  the 
filter,  the  washing  is  completed  with  a  dilute  solution  of  ammo- 
nium nitrate.  The  precipitate  is  dried,  ignited,  cooled,  and 
weighed. 

The  determinations  should  be  made  in  pairs,  and  one  of  the  pre- 
cipitates used  for  the  estimation  of  phosphoric  acid,  by  fusing  with 
a  little  sodium  carbonate,  and  the  other,  after  fusion  with  sodium 
carbonate,  is  dissolved  with  sulfuric  acid  and  the  iron  reduced 
and  titrated  with  potassium  permanganate  solution.  The  fil- 
trate from  the  iron  and  alumina  determination  is  evaporated 
to  a  small  bulk,  made  strongly  ammoniacal  and  allowed  to  stand 
for  some  time,  when  the  magnesia  present  separates  as  ammonium 
magnesium  phosphate,  which  is  determined  in  the  usual  way. 

If,  during  the  evaporation  of  the  filtrate,  any  flocculent  matter 
separates,  it  should  be  removed  by  filtration  and  examined  before 
precipitating  the  magnesia. 

211.  Variation  of  Marioni  and  Tasselli. —  The  old  and  classic 
method  of  separating  iron  and  alumina  in  the  presence  of  ammo- 
nium acetate  has  been  shown  to  be  subject  to  errors  by  Marioni 
and  Tasselli  in  the  following  respects  :97 

97  Le  Stazioni  sperimentali  agrarie  italiane,  1892,  23  :  31. 


24O  AGRICULTURAL  ANALYSIS 

1.  The  precipitation  of  a  small  quantity  of  calcium  phosphate 
with  the  ferric  and  aluminum  phosphates. 

2.  The  possible   precipitation   of  basic   phosphates   if   all   the 
iron  and  alumina  are  not  combined  with  phosphoric  acid  in  the 
mineral. 

3.  The  partial  solubility  of  ferric  and  aluminum  phosphates 
in  dilute  acetic  acid. 

4.  The   decomposition   of   ferric   orthophosphate   into   soluble 
acid  phosphate  and  insoluble  basic  salt  by  washing  with  boiling 
water. 

To  avoid  these  errors  the  following  procedure  is  proposed : 
From  one  to  five  grams  of  the  sample  according  to  its  richness 
in  phosphoric  acid  is  boiled  in  a  flask  for  10  minutes  with  15 
cubic  centimeters  of  strong  hydrochloric  acid,  and  afterwards 
diluted  with  a  double  volume  of  water.  A  few  crystals  of  potas- 
sium chlorate  are  added,  or  several  drops  of  nitric  acid,  and  the 
liquid  boiled  to  expel  chlorin.  The  solution  is  filtered  and  the  filter 
washed  until  the  volume  of  the  filtered  liquid  amounts  to  150 
cubic  centimeters.  After  cooling,  a  half-gram  of  neutral  ammo- 
nium phosphate  in  solution  is  added,  and  two  cubic  centimeters 
of  glacial  acetic  acid,  followed  by  ammonia,  drop  by  drop,  until 
a  slight  precipitate  persists  on  stirring.  The  mixture  is  made 
decidedly  alkaline  by  adding  ammonia  gradually  until  the  alkaline 
reaction  is  established.  Again  the  same  quantity  of  acetic  acid 
is  added  as  above,  well  shaken,  and  left  for  two  hours.  The  pre- 
cipitate is  collected  on  a  filter  and  washed  with  a  10  per  cent, 
ammonium  phosphate  solution.  The  precipitate  is  dissolved  by  a 
minimum  quantity  of  hydrochloric  acid  and  the  solution  collected 
in  the  same  vessel  in  which  the  precipitation  took  place.  A 
second  precipitation  is  conducted  just  as  described  above.  The 
precipitate  is  washed  as  above  described  and  ignited  at  a  dull  red 
heat.  Half  the  weight  obtained  represents  the  ferric  oxid  and 
alumina. 

Following  these  variations,  in  which  the  principal  novelty  is  the 
solvent  action  on  the  mixed  precipitates  produced  by  ammonia, 
by  which  all  are  dissolved  save  the  iron  and  aluminum  phosphates, 
the  authors  claim  to  get  accurate  results. 


METHOD  OF  KRUG  AND  MCELROY  241 

212.  Suggestion  of  Ogilvie. — When  a  phosphate  is  dissolved  in 
a  mineral  acid  preparatory  to  the  separation  of  the  various  sub- 
stances which  pass  into  solution,  most  authorities  advise  that  the 
solutions  be  brought  to  dryness  before  proceeding  to  separate  the 
calcium.    Some  analysts,  however,  neglect  this  part  of  the  process, 
and,  as  Ogilvie  has  shown,  with  a  chance  of  error.98     It  appears 
from  this  fact  that  in  the  analyses  of  the  majority  of  the  phos- 
phatic  products  in  use  for  manurial  purposes,  special  care  must  be 
exercised  to  procure  a  pure  and  perfectly  granular  precipitate  of 
magnesium  ammonio-phosphate,  either  by  evaporating  the  first 
solution  to  dryness,  or  by  separating  the  precipitate  which  forms 
on  the  addition  of  ammonia  to  the  solution  containing  citric  acid. 

213.  Method  of  Krug  and  McElroy. — Krug  and  McElroy  show 
that  when  sufficient  alcohol  is  added  to  precipitate  all  of  the  cal- 
cium sulfate  in  the  Glaser  method,  it  will  also  cause  a  precipitation 
of  a  considerable  quantity  of  iron,  by  means  of  which  the  calcium 
sulfate  will  be  colored."  The  presence  of  potassium  and  ammo- 
nium salts  also  affects  very  notably  the  precipitation  of  calcium. 
The  procedure  suggested,  in  order  to  avoid  these  sources  of  error, 
is  based  on  the  separation  of  the  phosphoric  acid  by  the  molyb- 
date  method  and  is  as  follows : 

One  hundred  cubic  centimeters,  equivalent  to  one  gram  of  the 
substance,  in  a  nitric  acid  solution,  are  placed  in  a  half-liter  flask 
and  a  solution  of  ammonium  molybdate  added  until  all  the  phos- 
phoric acid  has  been  precipitated.  The  addition  of  ammonium 
nitrate  will  hasten  the  separation  of  the  ammonium  phospho- 
molybdate.  The  liquid  should  be  allowed  to  stand  for  12 
hours.  The  flask  is  filled  to  the  mark,  the  contents  well 
shaken,  filtered  through  a  dry  filter,  and  duplicate  samples  of 
200  cubic  centimeters  each  of  the  filtrate  subjected  to  examination. 

A  small  quantity  of  ammonium  nitrate  is  dissolved  in  the 
liquid,  and  ammonia  cautiously  added,  keeping  the  solution  as 
cool  as  possible.  The  iron  and  alumina  are  precipitated  as 

98  Crookes,  Select  Methods  in  Chemical  Analysis,  4th  Edition,  1905  : 499. 

99  Journal  of  Analytical  and  Applied  Chemistry,  1891,  5  :  671. 
Zeitschrift  fur  angewandte  Chemie,  1891,  4  :  170,  243,  357. 
Zeitschrift  fur  analytische  Chemie,  1891,  30  :  206. 
Chemical  News,  1891,  63  :  251. 


242  AGRICULTURAL  ANALYSIS 

hydroxids.  The  mixed  hydroxids  are  collected  on  a  filter,  washed 
with  water,  the  filtrate  and  washings  being  collected  in  a  beaker. 

The  precipitate  is  dissolved  with  a  small  quantity  of  a  solution 
of  ammonium  nitrate  and  nitric  acid,  again  precipitated  with  am- 
monia, filtered,  washed,  ignited,  and  weighed.  This  treatment 
is  for  the  purpose  of  excluding  all  possibility  of  error  from  the 
presence  of  molybdic  anhydrid.  After  weighing,  the  mixed  oxids 
are  fused  with  sodium  bisulfate,  the  magma  dissolved  in  water,  and 
the  iron  determined  volumetrically  with  potassium  permanganate 
after  reduction  to  the  ferrous  state. 

McElroy  has  shown  later  that  even  the  molybdate  method  of 
separating  the  iron  and  alumina  from  phosphoric  acid  with  the 
improvements  as  first  suggested  by  Krug  and  himself,  may  not 
always  give  reliable  results.1  In  a  solution  containing  ferrous 
iron  equivalent  to  56.4  milligrams  of  ferric  oxid,  was  placed 
enough  of  a  solution  of  sodium  phosphate  to  correspond  to  100 
milligrams  of  phosphorus  pentoxid.  The  precipitate  was  dis- 
solved by  adding  nitric  acid,  oxidized  with  bromin  water,  and  the 
phosphoric  acid  thrown  out  with  ammonium  molybdate.  The  pre- 
cipitate was  washed  with  weak  nitric  acid  and  the  combined  fil- 
trate and  washings  neutralized  with  ammonia.  The  resultant  pre- 
cipitate was  dissolved  in  a  solution  of  ammonium  nitrate  and  nitric 
acid,  filtered,  and  again  precipitated  with  ammonia.  In  two  in- 
stances the  quantities  of  material  recovered  after  ignition  were 
56.9  and  57.3  milligrams,  respectively,  instead  of  the  theoretical 
amount,  viz.,  56.4  milligrams. 

When  the  work  was  repeated  after  the  addition  of  400  milli- 
grams of  calcium  oxid  the  weight  of  the  precipitate  recovered 
was  62.3  and  63.1  milligrams  in  duplicate  determinations.  Sim- 
ilar determinations  were  made  with  a  known  weight,  viz.,  35.6 
milligrams  of  alumina.  The  treatment  of  the  mixture  was  pre- 
cisely as  indicated  above  for  iron.  The  quantity  of  alumina  fin- 
ally obtained  was  28.9  and  29.3  milligrams,  respectively,  in 
duplicate  determinations.  When  the  lime  was  added,  however, 
the  weights  of  alumina  recovered  fell  to  19.8  and  20.6  milligrams 
respectively.  These  results  show  that  the  molybdate  method  for 
1  Journal  of  the  American  ChemicU  Society,  1895,  17  :  260. 


METHOD   OF   WYATT  243 

the  separation  of  iron  and  alumina  in  the  presence  of  a  large  ex- 
cess of  lime  and  phosphoric  acid  is  subject  to  widely  varying 
results,  but  that  the  error  due  to  the  excess  of  iron  in  the  weighed 
product  is  partly  corrected  by  the  one  due  to  the  deficiency  of 
alumina. 

214.  Method  of  Wyatt. — A  method,  formerly  very  extensively 
used  in  this  country,  both  in  private  laboratories  and  by  fertiliz- 
er factories,  for  determining  iron  and  alumina  is  described  by 
Wyatt.2  It  is  claimed  for  this  method,  which  is  a  modification 
of  the  acetate  process,  that,  while  it  may  not  be  strictly  accurate, 
yet  it  is  rapid  and  easy,  and  in  the  hands  of  trained  analysts 
yields  concordant  results.  Fifty  cubic  centimeters  of  the  first 
solution  of  the  sample  in  aqua  regia,  or  an  amount  thereof  equiv- 
alent to  one  gram  of  the  phosphate,  are  rendered  alkaline  by 
ammonia.  The  resulting  precipitate  is  first  redissolved  by  hydro- 
chloric acid,  and  then  a  slight  alkalinity  is  again  produced  with 
ammonia.  Fifty  cubic  centimeters  of  strong  acetic  acid  are  added, 
the  mixture  stirred,  placed  in  a  cool  place  and  left  until  cold. 
The  precipitate  is  separated  by  filtration  and  washed  twice  with 
boiling  water.  The  vessel  holding  the  filtrate  is  replaced  by  the 
beaker  in  which  the  precipitation  was  made.  The  precipitate 
is  dissolved  in  a  little  50  per  cent,  hot  hydrochloric  acid  and  the 
filter  washed  with  hot  water.  After  rendering  slightly  alkaline, 
as  in  the  first  instance,  the  treatment  with  acetic  acid  is  repeated 
as  described.  The  precipitate  is  washed  this  time,  twice  with  cold 
water  containing  a  little  acetic  acid  and  three  times  with  hot  water. 
The  precipitate  is  dried,  ignited,  and  weighed  as  iron  and  alumi- 
num phosphate.  Half  of  this  weight  may  be  taken  to  represent  the 
quantity  of  iron  and  aluminum  oxids,  for  all  the  general  purposes 
of  the  factory  or  the  control  of  the  daily  work  at  the  mines. 

To  separate  the  iron  and  alumina  the  ignited  precipitate  just 
described  is  dissolved  in  hot  hydrochloric  acid,  filtered  into  a  100 
cubic  centimeter  flask,  and  made  up  to  the  mark  by  hot  wash- 
water. 

The  phosphoric  acid  is  determined  in  one-half  of  the  filtrate 
and  in  the  remaining  half  the  iron  is  reduced  with  zinc  and 
*  Phosphates  of  America,  4th  Edition,  1892  :  150. 


244  AGRICULTURAL   ANALYSIS 

determined  with  potassium  permanganate  in  the  usual  way. 
The  phosphoric  acid  and  iron  having  been  thus  determined,  the 
alumina  is  estimated  by  difference.  The  chief  objection  to  this 
process  is  in  the  excessive  quantity  of  acetic  acid  used  and  the 
danger  of  solution  of  the  precipitated  phosphates  caused  thereby. 

215.  Estimation  of  the  Lime  and  Magnesia. — The  filtrate  and 
washings  from  the  first  precipitation,  (paragraph  213)  of  iron  and 
alumina  in  the  method  (of  Krug  and  McElroy,  above  described, 
are  collected  and  sufficient  ammonium  oxalate  is  added  to  precipi- 
tate the  calcium.       The  precipitated  calcium  is  very   fine  and 
should  be  collected  on  a  gooch,  without  pressure.     The  filtrate 
and  washings  from  the  calcium  precipitate  are  again  collected, 
and  a  solution  of  sodium  phosphate   added  to  precipitate   the 
magnesia.     The  solution  must  be  kept  cool  and  slightly  alkaline 
with  ammonia  during  the  above  operations  in  order  to  prevent 
the  separation  of  molybdic  anhydrid. 

216.  Separation  of  Iron  and  Aluminum  Phosphates  from  the 
Calcium  Compound. — There  are  many  points  of  difference  noted 
in  the  descriptions  given  by  authors  of  the  deportment  of  the  iron 
and  aluminum  phosphates  in  presence  of  a  large  excess  of  the 
calcium  salt.     Especially  is  this  true  of  the  statements  made  by 
Hess  and  Glaser.3     The  subject  is  of  such  importance,  from  a 
analytical  point  of  view,  as  to  merit  a  careful  study. 

In  the  laboratory  of  the  Division  of  Chemistry  a  thorough  in- 
vestigation of  the  mutual  deportment  of  these  three  phosphates 
has  been  made  by  Brown  with  the  following  results  :*  When 
a  mixture  containing  a  known  weight  of  the  salts  is  treated  exact- 
ly as  Hess  directs,  in  no  case  is  there  a  complete  separation  of  the 
iron  aluminum  phosphate  from  the  calcium  salt.  In  order  to  dis- 
cover the  cause  of  the  failure,  pure  solutions  of  calcium  and  iron 
aluminum  phosphates  are  treated  under  identical  conditions  by 
the  necessary  reagents.  Fifty  cubic  centimeters  of  a  solution  of 
calcium  phosphate,  containing  about  one  gram  of  the  salt,  are 
treated  with  100  cubic  centimeters  of  water  and  50  cubic  centime- 
ters of  the  commercial  ammonium  acetate  containing  150  grams 

*  Zeitschrift  fur  angewandte  Chemie,  1894,  7  :  679,  701  ;  1889,  2  :  636. 

*  Report  to  Author  by  W.  G.  Brown,  1894. 


IRON    AND   ALUMINUM    PHOSPHATES  •          245 

of  the  salt  in  a  liter.  An  immediate  precipitate  is  produced  at 
ordinary  temperatures,  and  on  heating  to  60°  it  becomes  abundant. 
The  addition  of  ammonium  chlorid,  phosphate,  and  nitrate  in  suc- 
cessive portions,  does  not  prevent  the  precipitation.  Making 
the  solution  more  dilute  lessens  the  difficulty.  When  20  cubic 
centimeters  of  a  10  per  cent,  solution  of  ammonium  phosphate 
are  first  added,  followed  by  the  usual  quantity  of  ammonium 
acetate,  a  clear  crystalline  precipitate  is  sometimes  observed. 
.Experience  also  shows  that  the  trouble  is  not  due  to  an  excess 
of  the  ammonium  acetate. 

In  treating  a  solution  of  iron-aluminum  phosphate,  in  similar 
circumstances,  with  the  ammonium  acetate,  it  is  found  that  a 
complete  precipitation  takes  place. 

Since  diluting  the  solution  of  the  calcium  salt  diminishes  its 
tendency  to  form  a  precipitate  with  the  ammonium  acetate,  the 
true  method  of  separation  seems  to  lie  in  that  direction.  The 
calcium  salt  is  held  completely  in  solution  when  the  separation 
is  made  in  the  following  way : 

The  solution  containing  the  mixed  phosphates  is  diluted  so  as 
to  contain  not  more  than  one  gram  thereof  in  half  a  liter.  To 
this  is  added  one  drop  of  methyl  orange,  and  afterwards 
ammonium  hydroxid,  until  a  very  slight  precipitate  is  formed. 
The  mixture  is  heated  to  70°  and  from  20  to  25  cubic  centimeters 
of  a  25  per  cent,  solution  of  acid  ammonium  acetate  are  added, 
enough  to  change  the  rose  color  of  the  indicator  to  orange.  The 
iion-aluminum  phosphate  is  separated  by  filtration  and  washed 
with  a  hot  five  per  cent,  solution  of  ammonium  nitrate. 

The  washed  precipitate  shows  no  impurity  due  to  calcium,  as  is 
proved  by  dissolving  it,  reprecipitating  and  filtering,  adding 
ammonium  hydroxid  to  the  filtrate,  and  heating  for  a  long  time. 
Sometimes  a  slight  troubling  of  the  clear  liquid  may  be  observed 
which  may  be  due  to  a  slight  solubility  of  the  iron-aluminum 
phosphate  in  washing,  an  accident  that  may  occur  if  the  tem- 
perature be  allowed  to  fall  below  70°,  but  no  weighable  amount 
of  material  is  obtained.  If  due  to  calcium  phosphate,  a  greater 
dilution  in  the  first  precipitation  will  remove  even  this  mere  trace 
of  that  salt.  In  the  above  conditions  the  contamination  of  the 


246          •  AGRICULTURAL  ANALYSIS 

iron-aluminum  precipitate  with  calcium  phosphate  may  be  en- 
tirely avoided.  The  problem  of  separating  the  phosphoric  acid 
by  the  citrate  method,  followed  by  a  destruction  of  the  citric  acid 
in  the  filtrate  by  combustion  with  sulfuric  acid  according  to  the 
kjeldahl  process,  and  final  separation  of  the  iron  and  alumina  in 
the  residues  was  already  under  way  when  our  attention  was  called 
to  substantially  the  same  process  described  by  Jean.5  The  meth- 
cd  merits  a  further  critical  examination. 

217.  Methods  of  the  German  Fertilizer  Association. — The  meth- 
ods of  determining  phosphoric  acid  and  other  constituents  in  min- 
eral phosphates  according  to  the  directions  prescribed  by  the 
Union  of  German  Fertilizer  Manufacturers  differ  only  in  unim- 
portant details  from  other  German  methods  described.6 

Water-Soluble  Phosphoric  Acid. — This  method  is  applied  to 
superphosphate,  phosphate  precipitates  and  raw  phosphates,  but 
is  not  applicable  to  phosphatic  slags.  The  extraction  is  performed 
upon  20  grams  of  superphosphate  in  a  liter  flask.  The  sample  is 
covered  with  800  cubic  centimeters  of  water,  shaken  for  30 
minutes  and  filled  up  to  the  mark.  The  ordinary  shaking  ma- 
chine is  used.  In  cases  of  double  phosphates  they  should  be  pre- 
viously boiled  with  nitric  acid  in  order  to  convert  any  pyrophos- 
phate  into  orthophosphate.  It  is  recommended  that  the  final 
precipitation  of  the  phosphoric  acid  be  conducted  according  to  the 
usual  molybdic  acid  method  with  only  a  few  unimportant  varia- 
tions. 

The  Citrate  Method. — In  lieu  of  the  molybdic  acid  method  the 
Union  of  German  Fertilizer  Manufacturers  also  recommends 
the  citrate  method,  which  is  carried  out  as  has  already  been  de- 
scribed, with  unimportant  variations. 

Volumetric  Method  by  Titration  with  Uranium  Salts. — This 
method,  although  recognized  as  being  a  very  old  one,  is  recom- 
mended in  cases  where  there  are  no  large  quantities  of  iron  and 
alumina.  The  method  as  used  does  not  differ  in  any  marked  re- 
pect  from-  that  already  given. 

Citrate-Soluble  Phosphoric  Acid. — The  method  of  securing  the 

5  Journal  de  Pharmacie  et  de  Chirnie,  1895,  [6],  1  :  99. 

Chemisches  Central-Blatt,  1895,  1  :  562. 
*  Methoden  zur  Untersuchung  der  Kunstdiingemittel,  1903  :  2. 


METHODS  OF  GERMAN   FERTILIZER  ASSOCIATION  247 

phosphoric  acid  which  is  soluble  in  a  standard  solution  of  citrate 
of  magnesia  is  that  of  Wagner,  which  has  already  been  fully 
described. 

Free  Phosphoric  Acid.-^-Two  methods  are  given  for  determin- 
ing the  free  phosphoric  acid  which  may  be  present  in  a  fertilizer. 
The  titration  method  is  carried  out  as  follows  :  The  free  phosphoric 
acid  is  extracted  with  the  water-soluble  as  already  described. 
An  amount  corresponding  to  one  gram  of  the  original  substance 
is  diluted  to  about  100  cubic  centimeters  and  two  or  three  drops 
of  an  aqueous  solution  of  methyl  orange  made  up  in  the  propor- 
tion of  one  part  of  pure  salt  to  100  parts  of  water  added.  The  titra- 
tion is  accomplished  by  means  of  soda  lye  of  known  strength  until 
the  red  color  is  converted  into  yellow.  In  the  standardizing  of 
the  soda  lye  a  pure  solution  of  phosphoric  acid  of  known  strength 
is  used  and  in  about  the  same  dilution  as  that  expected  in  the 
fertilizer.  The  change  of  color  takes  place  immediately  when  the 
primary  salt  is  formed  from  the  phosphoric  acid  according  to  the 
following  formula : 

H3PO4+NaHO=:NaH2P(Vf-H2O. 

It  is  advisable  to  pass  beyond  the  titration  mark  in  the  addi- 
tion of  a  soda  lye ;  afterwards  separate  the  precipitate  by  filtra- 
tion and  titrate  back  the  excess  of  alkali  with  a  standard  acid  in 
an  aliquot  part  of  the  filtrate.  By  this  method  the  change  of 
color  can  be  more  easily  recognized.  This  back  titration,  how- 
ever, is  attended  with  an  error  due  to  the  fact  that  a  portion  of 
the  excess  of  soda  lye  may  adhere  to  the  precipitate  and  the  more 
so  in  proportion  as  the  amount  of  excess  is  greater.  A  slight 
correction,  therefore,  should  be  made,  which  is  determined  by  ex- 
periments, in  order  to  avoid  obtaining  too  high  a  content  of  free 
acid  by  this  method.  In  the  second  method  the  usual  gravimetric 
process  with  molybdate  solution  is  used. 

Estimation  of  Iron  and  Alumina. — This  is  conducted  according 
to  the  method  of  Glaser  and  Jones  as  has  already  been  described. 

Estimation  of  Flitorin. — For  the  purpose  of  determining  fluo- 
rin  the  method  of  Fresenius  and  Richters  is  employed.  There  are 
two  variations  of  the  method,  one  for  raw  phosphate  and  the 
other  for  superphosphate.  In  the  case  of  a  raw  phosphate  five 


248  AGRICULTURAL  ANALYSIS 

grams  are  treated  in  a  platinum  dish  with  20  cubic  centimeters 
of  a  20  per  cent,  acetic  acid  on  a  water  bath  until  all  the  carbonic 
acid  is  eliminated.  The  mass  is  then  evaporated  to  dryness  and 
ignited  in  order  to  remove  the  moisture  and  any  organic  substance 
that  may  be  present.  The  ignited  mass  is  mixed  with  about  20 
grams  of  pure  ignited  quartz  sand,  then  placed  in  a  dry  flask  of 
about  250  cubic  centimeters  capacity  and  treated  with  40  cubic 
centimeters  of  pure  concentrated  monohydrate  sulfuric  acid.  The 
flask  is  stoppered  in  such  a  way  as  to  connect  with  it  two  U-tubes 
filled  with  water  and  is  then  heated  for  four  hours  to  140°. 
After  the  decomposition  is  completed  a  stream  of  warm  air 
amounting  in  all  to  about  one  liter  is  drawn  slowly  through  the 
apparatus.  The  contents  of  the  U-tubes  are  poured  into  a  beaker 
and  the  hydrofluosilicic  acid  is  treated  with  one-half-normal 
soda-lye,  using  phenolphthalein  as  indicator.  In  case  there  are 
only  small  quantities  of  fluorin,  namely,  only  one-half  of  one  per 
cent.,  it  is  advisable  to  add  some  fluorid  of  calcium  of  known 
composition  and  the  quantity  of  fluorin  obtained  is  corrected  by 
deducting  the  added  fluorin  from  the  total  secured.  In  the  case 
of  superphosphate  there  is  added  to  the  five  grams  of  substance 
a  sufficient  amount  of  milk  of  lime  to  produce  a  distinct  alkaline 
reaction.  The  mixture  is  then  evaporated  and  ignited  as  above. 
After  cooling,  the  mass  is  rubbed  with  a  pestle  and  poured  through 
a  dry  funnel  into  the  decomposition  flask  above  mentioned.  The 
platinum  dish  and  funnel  are  repeatedly  rinsed  with  finely  ground, 
ignited  quartz  powder.  The  rest  of  the  process  is  carried  on  as 
has  just  been  described. 

218.  French  Method  for  Mineral  Phosphates. — The  French  offi- 
cial methods  are  adapted  to  determine  phosphoric  acid  in  various 
forms.7 

First — Mineral  phosphates  composed  chiefly  of  dry  calcium 
phosphate  mixed  in  a  greater  or  less  degree  with  carbonate  of 
lime,  silicious  materials,  etc.,  and  in  different  degrees  of  fineness 
as  secured  by  the  usual  mechanical  means. 

Second — Phosphate  of  fresh  bone,  phosphate  of  degelatinized 
bone,  animal  black,  char  from  the  sugar  refining  factories,  etc. 

7  Grandeau,  Tratte  d'Analyse  des  Matures  agricoles,  3d  Edition,    1897, 
1  =443- 


METHOD  OF  LASNE  249 

Third — Phosphate  in  products  such  as  farm-yard  manure,  poud- 
rette,  guano,  etc. 

Fourth — Phosphates  which  have  been  treated  by  chemical  pro- 
cesses producing  superphosphates  whether  from  bone  or  mineral 
phosphates,  precipitated  phosphates,  ammoniaco-magnesium  phos- 
phates, etc. 

Fifth — Phosphates  which  are  produced  in  metallurgical  opera- 
tions, such  as  basic  slag,  etc. 

The  methods  employed  for  these  various  processes  are  not  es- 
sentially different  from  those  which  are  already  described.  There 
are  certain  slight  variations  in  the  methods  of  preparation  which 
are  of  interest  but  do  not  introduce  any  new  principles  or  methods 
of  procedure. 

219.  Method  of  Lasne.8 — With  ordinary  phosphates,  contain- 
ing as  much  as  three  per  cent,  of  alumina  a  convenient  quantity 
to  use  is  two  grams.  If  the  phosphate  be  poor  in  alumina,  a 
larger  quantity  may  be  employed.  The  phosphate  in  a  fine  powder 
is  dissolved  in  hydrochloric  acid  with  or  without  the  addition  of 
nitric  acid,  as  may  be  desired.  The  solution  is  evaporated  to 
dryness,  moistened  several  times  with  hydrochloric  acid  and 
again  dried  to  render  the  silica  totally  insoluble.  The  soluble 
parts  of  the  residue  are  taken  up  in  dilute  hydrochloric  acid 
(one  part  strong  acid  to  20  of  water)  so  as  not  to  have  more  than 
1.5  grams  of  HC1  to  each  gram  of  phosphate.  The  solution  may 
be  either  filtered  and  washed  or  made  up  to  a  known  volume,  fil- 
tered through  a  dry  filter  and  an  aliquot  part  of  the  filtrate  em- 
ployed for  the  subsequent  analysis. 

A  convenient  quantity  of  the  filtrate  to  employ  is  one  which  cor- 
responds to  1.25  grams  of  the  original  phosphate  in  case  two 
grams  have  been  taken. 

Meanwhile,  there  should  be  prepared  a  solution  of  five  grams 
of  caustic  soda  free  of  alumina  and  silica.  This  is  dissolved  in  a 
nickel  dish  with  about  10  cubic  centimeters  of  water.  The  quan- 
tity of  soda  to  be  employed  is  to  be  calculated  as  follows :  Two 
grams  per  gram  of  the  phosphate  and  one  gram  for  each  100 
cubic  centimeters  of  the  final  volume  employed.  There  is  added 
8  Bulletin  de  la  Societ^  chimique  de  Paris,  1896,  [3],  15:6,  118,  146, 
237- 


250  AGRICULTURAL   ANALYSIS 

to  the  liquor  one  gram  of  phosphate  of  soda  containing  about  20 
per  cent,  of  phosphoric  acid.  It  is  necessary  to  call  attention  to 
the  fact  that  the  liquor  is  to  contain  enough  of  phosphoric  acid 
to  completely  saturate  the  lime  and  that  the  acid  be  in  excess  at 
least  one  decigram.  It  will  be  necessary,  therefore,  to  increase 
a  little  the  quantity  indicated  if  the  phosphate  is  very  rich  in  car- 
bonate. For  certain  chalky  phosphates,  it  will  be  necessary  to  use 
as  much  as  two  grams  of  the  phosphate  of  soda. 

The  soda  liquor  thus  prepared  is  poured  in  a  fine  stream  into 
the  solution  of  the  phosphate  prepared  a?  above,  and  its  constant- 
ly stirred  with  a  metal  spatula.  After  the  addition  of  the  soda,  the 
mixture  is  heated  to  about  100°  for  half  an  hour,  but  it  is  pref- 
erable to  prolong  the  heating  for  an  hour,  stirring  from  time  to 
time.  After  cooling,  the  mixture  is  placed  in  a  flask  marked  at 
250  cubic  centimeters,  and  the  volume  completed  with  water  to 
the  mark. 

To  be  able  to  take  account  of  the  volume  of  the  precipitate,  a 
half  cubic  centimeter  of  water,  in  addition,  is  added.  The  mix- 
ture is  strongly  shaken  several  times  and  left  for  half  an  hour 
in  ordec  to  permit  the  complete  diffusion  of  the  liquid  through- 
out the  precipitate.  The  contents  of  the  flask  are  next  poured 
upon  a  dry  filter  and  200  cubic  centimeters  of  the  filtrate  cor- 
responding to  one  gram  of  the  original  phosphate,  in  case  two 
grams  have  been  used,  employed  for  the  estimation  of  the  alum- 
ina. 

It  has  been  proved  that  by  this  treatment  all  the  bases,  except 
alumina,  which  can  be  present,  have  been  retained  as  phosphates, 
while  the  phosphate  of  alumina  has  remained  completely  soluble. 

The  200  cubic  centimeters  of  the  filtrate,  obtained  as  above,  are 
placed  in  an  erlenmeyer  and  hydrochloric  acid  added  until  the 
precipitate  at  first  formed  is  just  dissolved.  There  are  then  added 
25  cubic  centimeters  of  a  solution  of  ammonium  chlorid  contain- 
ing 125  grams  per  liter.  Ammonia  is  then  added  until  there  is 
formed  a  precipitate  which  persists.  The  mixture  is  next  heated 
to  near  ebullition  and  with  great  care  a  solution  of  dilute  ammonia 
is  added.  The  heated  mixture  should  not  give  off  more  than  a 
feeble  odor  of  ammonia,  and  it  is  highly  important  that  the  ammo- 


METHOD  OV  LASNE  251 

nia  be  not  added  in  excess.  The  mixture  is  then  boiled  for  five 
minutes.  It  is  allowed  to  rest  for  some  moments  and  then  fil- 
tered still  hot.  The  precipitate  is  drained  upon  the  filter  and  the 
filter  and  the  precipitate  in  the  erlenmeyer  washed  only  once. 
The  precipitate  both  on  the  filter  and  remaining  in  the  erlen- 
meyer is  then  redissolved  in  from  20  to  25  cubic  centimeters  of 
hydrochloric  acid  diluted  to  one-twentieth  and  heated  to  100°. 
The  solution  in  the  erlenmeyer  and  the  wash-waters  from  the 
filter  are  united  in  an  erlenmeyer  and  treated  with  3.5  cubic  centi- 
meters of  a  10  per  cent,  solution  of  ammonium  phosphate.  This 
solution  should  contain  about  53.4  grams  of  phosphoric  acid  per 
liter.  There  is  then  0.187  gram  of  phosphoric  acid  in 
excess,  and  this  condition  should  be  realized  as  nearly 
as  possible.  Ammonia  is  added  until  a  light  precipitate 
persists  which  is  dissolved  with  great  care  in  a  few  drops  of 
dilute  hydrochloric  acid,  in  such  a  manner  that  the  mixture 
clears  up  gradually  after  agitation.  This  having  been  accom- 
plished, 1.5  grams  of  hyposulfite  of  ammonia  are  added,  or  10 
cubic  centimeters  of  a  solution  of  this  salt  containing  150  grams 
per  liter.  The  volume  of  the  mixture  is  completed  to  about  250 
cubic  centimeters,  and  afterwards  it  is  carried  to  boiling,  which  is 
continued  30  minutes,  the  volume  of  water  being  kept  up  by  oc- 
casional additions.  At  the  end  of  this  time  the  precipitation  is 
easily  completed.  Nevertheless,  in  order  to  have  a  greater  cer- 
tainty, there  should  be  added,  after  suspending  the  boiling  for  a 
moment,  from  four  to  five  drops  of  a  saturated  solution  of  ammo- 
nium acetate.  This  salt,  which  in  large  quantities  dissolves  phos- 
phate of  alumina,  has  no  influence  in  so  small  a  quantity.  The  boil- 
ing is  then  continued  for  five  minutes  longer.  After  allowing  to 
settle  for  a  few  minutes  the  liquor  is  filtered  still  hot.  The  pre- 
cipitate does  not  adhere  to  the  walls  of  the  flask  and  is  easily 
collected  upon  the  filter  where  it  is  washed  seven  or  eight  times 
with  boiling  water.  The  collected  precipitate,  after  drying,  is 
incinerated  and  kept  at  a  white  heat  for  15  minutes  in  the  blow- 
pipe before  weighing.  The  composition  of  this  precipitate  is  ex- 
actly P2Or,Al.;PO3.  The  weight  of  the  precipitate  multiplied  by 
0.418  gives  the  weight  of  the  alumina  therein. 


252  AGRICULTURAL  ANALYSIS 

There  is  in  the  second  precipitate  mentioned  above  a  slight  loss 
of  alumina  which  precise  experiments  have  shown  me  to 
be  0.8  milligram.  This  is  due  to  a  solubility  which  depends 
only  on  the  volume  of  the  liquid  and  not  upon  the  weight  of  the 
precipitate.  Eight-tenths  of  a  milligram  should,  therefore,  be 
added  to  the  weight  of  the  alumina  as  determined  above. 

220.  Comparison  of  Methods  of  Estimation  of  Iron  and  Alu- 
mina in  Phosphates. — Blattner,  in  collaboration  with  Brasseur,  at 
Lille,  has  made  a  comparative  examination  of  some  of  the  methods 
in  use  of  determining  the  iron  and  alumina  in  natural  phosphates. 
They  have  examined  the  following  processes : 

1.  The  process  of  Maret  and  Delattre,  which  is  very  extensively 
employed  in  France. 

2.  The  method  of  E.  Glaser. 

3.  The  method  of  H.  Lasne. 

4.  The  method  of  J.  Grueber. 

The  results  of  their  studies  are  as  follows : 

1.  The  method  of  Maret  and  Delattre  gives  results  wrhich  are 
not  accurate,  the  quantities  of  iron  and  alumina  being  usually 
too  small. 

2.  The  method  of  E.  Glaser,  embracing  separate  determinations 
for  the  oxid  of  iron  and  alumina  is  able  to  give  exact  results, 
but  if  the  phosphates  contain  manganese  this  substance  goes  also 
in  the  precipitate  and  is  counted  as  alumina,  and  as  a  result  the 
figures  for  alumina  obtained  by  the  method  of  Glaser  are  too  high 
when  manganese  is  present. 

3.  The  method  of  Lasne  gives  results  which  are  rigorously  exact 
when  conducted  with  reagents  which  are  perfectly  pure.     It  is 
the  most  exact  method  known  up  to  the  present  time,  and  has  been 
tried  by  the  authors  in  the  most  minute  detail.     It  can  be  regarded 
as  a  standard  method. 

4.  The  method  proposed  by  Grueber  appears  to  be  an  abridge- 
ment of  the  method  of  Lasne.     The  authors,  however,  prove  that 
it  does  not  give  correct  results.     Grueber  applied  it  to  phos- 
phates which  were  prepared  by  synthesis  and  which  contained 
only  certain  of  the  matters,  and  not  at  all,  which  enter  into  the 
composition  of  natural  phosphates.    Where  a  great  deal  of  lime 


ESTIMATION  OF  ALUMINA  AND  FERRIC  OXID  253 

is  present,  by  the  modification  of  Grueber  no  alumina  at  all  is 
obtained  sometimes,  when  it  may  be  present  to  the  extent  of  half 
a  per  cent.  The  results  of  the  investigation  favor  entirely  the 
adoption  of  the  method  of  Lasne  to  the  exclusion  of  the  others.9 

221.  The  Estimation  of  Alumina  and  Ferric  Oxid  in  Natural 
Phosphates. — The  search  for  an  accurate  and  rapid  method  for 
the  determination  of  alumina  and  iron  oxid  in  the  presence  of 
phosphoric  acid  has  occupied  the  attention  of  analysts  for  years, 
and  many  methods  have  been  proposed  for  this  difficult  opera- 
tion. It  may  be  said  generally  that  even  those  methods  that 
have  stood  the  tests  of  extended  use  have  not  escaped  severe 
criticism;  they  are  only  accurate  within  narrow  and  rigidly  de- 
fined limits  or  they  are  tedious  and  time-consuming.10 

Aside  from  its  interest  from  the  scientific  point  of  view,  this 
subject  is  of  importance  in  its  technical  and  commercial  aspects. 
The  value  of  raw  mineral  phosphates  is  judged  largely  by  their 
content  of  alumina  and  iron. 

In  phosphatic  slags  the  estimation  of  these  oxids  is  more 
difficult,  though  possibly  not  so  important. 

Sources  of  Error  in  the  Older  Methods. — The  Glaser  alcohol, 
the  acetate  with  its  various  modifications,  and  the  caustic  alkali 
methods  as  carried  out  by  Lasne,  Lichtschlag  and  Gladding, 
have  all  been  criticised  and  the  sources  of  error  pointed  out. 

1.  In  the  Glaser  alcohol  method  the  precipitation  of  manganese 
with  the  iron  and  aluminum  phosphates  and  the  solubility  of  the 
phosphates   in  the  wash-water  are  important  sources  of  error. 
Probably  the  manganese  can  be  eliminated  by  a  second  precipita- 
tion in  the  presence  of  a  large  amount  of  ammonium  chlorid. 
Possibly  the  presence  of  a  large  amount  of  ammonium  sulfate 
may  also  affect  the  accuracy  of  this  method,  in  those  cases  where 
the  excess  of  ammonia  is  completely  removed  by  boiling.     Alumi- 
num phosphate  is  noticeably  soluble  in  a  strong  sulfate  solution, 
which  is  neutral  or  faintly  acid  from  SO2. 

2.  In  the  acetate  method  and  its  variations  there  is  an  error 
•caused  by  the  precipitation  of  the  lime  with  the  iron  and  alu- 

9  Chemiker-Zeitung,   1897,2!  1*414. 

10  Veitch,  Journal  of  the  American  Chemical  Society,  1900,  22  :  246. 


254  AGRICULTURAL  ANALYSIS 

minum  phosphates,  the  solubility  of  aluminum  phosphate  in  cold 
acetate  solutions,  and  the  solubility  and  dissociation  of  iron  and 
aluminum  phosphates  in  water.11  Also  when  the  phosphates  are 
fused  with  sodium  carbonate,  and  the  iron  determined  by  pre- 
cipitation with  ammonia,  the  contamination  of  the  iron  with 
calcium  phosphate,  which  is  not  always  entirely  decomposed  by 
fusion,  is  a  source  of  error.  Of  these  the  most  serious  are  the 
first  and  last  mentioned. 

3.  In  the  caustic  alkali  methods  there  is  danger  of  some  of 
the  aluminum  being  held  by  the  voluminous  precipitate  pro- 
duced by  the  alkali ;  there  is  also  danger  of  alumina  being  pre- 
cipitated if  much  carbon  dioxid  is  absorbed.  Lasne  and  Licht- 
schlag  have  shown  that  while  the  method  is  long,  it  gives  accu- 
rate results  if  properly  conducted.  Blattner  and  Brasseur  have 
investigated  the  more  important  methods  and  conclude  :12 

The  acetate  method  should  be  discontinued;  figures  for  alum- 
ina are  nearly  always  too  low. 

The  Glaser  method  (alcohol)  gives  accurate  results  in  the 
absence  of  manganese. 

The  caustic  soda  method,  as  carried  out  by  Lasne,  gives  exact 
results. 

In  view  of  these  many  sources  of  error  in  the  conventional 
methods,  considerable  time  has  been  devoted  to  the  study  of  a 
method  that,  it  is  hoped,  is  free  from  most  of  the  above  men- 
tioned objections.  It  is  an  adaptation,  so  far  as  possible,  of  the 
good  points  of  the  present  best  methods.  From  the  precipita- 
ting reagent  used,  it  may  be  designated  the  thiosulfate  method. 

The  use  of  a  soluble  thiosulfate  for  the  separation  of  alumina 
from  iron  and  aluminum  from  several  other  metals  seems  to  be 
due  to  Chancel.13  Later  it  was  used  by  Stead  and  by  Carnot; 
by  the  latter  for  the  separation  of  aluminum  as  phosphate,  in- 
the  presence  of  ammonium  acetate,  from  iron.14  Lasne  also  uses 
it  to  precipitate  aluminum  phosphate  in  the  presence  of  am- 

11  Chemiker-Zeitung,  1897,  21  :  264. 

11  Bulletin  de  la  Soci£t£  chimique  de  Paris,  1897,  [3],  17  :  760. 

18  Comptes  rendus,  1858,  46  :  987. 

14  Blair,  Chemical  Analysis  of  Iron,  6th  Edition,   1903,  :  196. 


ESTIMATION  OF  ALUMINA  AND  FERRIC  OXID  255 

monium  acetate,  after  removing  iron,  lime,  etc.,  with  caustic  soda.13 

The  thiosulfate  has  nothing  to  do  with  the  precipitation,  ex- 
cept that  it  is  an  exact  method  of  obtaining  the  desired  neu- 
trality. Thomson  has  devised  a  method  in  which  he  makes  use 
of  this  principle,  neutralizing  with  ammonia  and  using  a  delicate 
indicator  to  determine  neutrality.16 

Study  of  the  Proposed  Method. — One  of  the  first  problems  pre- 
.sented  in  the  study  of  any  method  for  the  determination  of 
alumina  as  phosphate  is  the  composition  of  the  ignited  phosphate. 
While  there  is  a  general  agreement  that  the  normal  phosphate 
is  only  obtained  in  the  presence  of  an  excess  of  phosphoric  acid, 
It  is  not  certain  that  it  is  always  obtained,  even  under  these  condi- 
tions.17 

Wash  Solutions. — It  seems  that  the  true  solution  of  this  prob- 
lem can  only  be  obtained  by  a  study  of  the  solutions  used  in  wash- 
ing the  precipitate.  Besides  waters  of  all  temperatures,  solu- 
tions of  various  salts,  such  as  five  per  cent,  ammonium  nitrate, 
ammonium  chlorid,  one  per  cent,  ammonium  nitrate  plus  0.02  per 
cent,  ammonium  phosphate,  and  dilute  ammonium  acetate,  have 
"been  proposed  and  used  by  many  investigators.  These  various 
washes  possibly  account  for  the  variations  from  the  normal,  so 
fiequently  noted.  The  recently  precipitated  phosphates  of  iron 
and  aluminum,  when  freed  from  adhering  salts,  are  slightly  solu- 
ble, or  rather  are  dissociated,  in  water  of  any  temperature.  Those 
who  have  apparently  used  water  successfully  as  a  wash  probably 
did  not  wash  enough,  only  three  or  four  times,  to  remove  the 
adhering  salts.  Cold  ammonium  or  sodium  acetate  also  slowly 
dissolves  aluminum  phosphate. 

The  effects  of  the  following  wash  liquors  have  been  studied: 

Water  at  from  60°  to  70°  C. 

Five  per  cent,  ammonium  nitrate  at  from  60°  to  70°  C. 

One  per  cent,  ammonium  nitrate  at  from  60°  to  70°  C. 

Five  per  cent,  ammonium  nitrate  and  0.02  per  cent,  ammonium 
phosphate  at  from  60°  to  70°  C. 

t5  Bulletin  de  la  Socie'te'  chimique,  de  Paris,  1896.  [3],  15  :  118. 
16  Journal  of  the  Society  of  Chemical  Industry.  1896,  15  :  868. 
117  Chemiker-Zeitung,  1897,  21  :  264. 

Blair,  Chemical  Analysis  of  Iron,  6th  Edition,  1906  :  196. 

.Sooth  Carolina  Agricultural  Experiment  Station,  Bulletin  2,  1891. 


256  AGRICULTURAL  ANALYSIS 

Method  of  Study. — Various  quantities  of  the  pure  aluminum 
sulfate  are  placed  in  a  12-ounce  beaker  with  a  solution  of  two 
grams  of  ammonium  phosphate,  the  resulting  precipitate  dis- 
solved in  hydrochloric  acid,  and  25  cubic  centimeters  of  a  50 
per  cent,  solution  of  ammonium  chlorid  added.  The  solution  is 
made  alkaline  with  ammonia  and  the  precipitate  just  dissolved 
with  hydrochloric  acid,  noting  approximately  the  number  of  cubic 
centimeters  required  after  the  solution  has  become  acid ;  the  solu- 
tion is  diluted  to  about  250  cubic  centimeters,  and  for  each  cubic 
centimeter  of  hydrochloric  acid  added  to  the  acid  solution  five 
cubic  centimeters  of  a  50  per  cent,  solution  of  ammonium  thiosul- 
fate  were  added  dropwise,  the  beaker  covered  with  a  watch- 
glass,  the  solution  boiled  half  an  hour,  filtered,  washed,  dried 
and  ignited  to  constant  weight. 

Washing  20  times  with  five  per  cent,  ammonium  nitrate  gives 
practically  theoretical  results.  As  many  as  50  washings  with 
this  solution  give  results  slightly  low,  but  still  good.  The  other 
solutions  were  rejected,  as  they  showed  a  decided  solvent  effect, 
except  the  ammonium  nitrates  plus  ammonium  phosphate,  upon 
prolonged  washing.  Twenty  washings  were  required  to  free  the 
precipitate  from  chlorids,  sulfates,  and  ammonium  phosphate. 
In  all  succeeding  work  five  per  cent,  ammonium  nitrate  was  used, 
washing  20  times.  Long  heating  with  the  blast  from  10  to  20 
minutes  was  required  to  reduce  to  constant  weight. 

Composition  of  the  Ignited  Aluminum  Phosphate. — The  phos- 
phoric acid  in  the  aluminum  phosphate,  washed  20  times  with 
five  per  cent,  ammonium  nitrate,  was  carefully  determined  by 
precipitation  with  molybdate  solution,  washing  the  precipitate  of 
ammonium  phosphomolybdate  with  dilute  nitric  acid,  and  wash- 
ing the  final  precipitate  free  of  chlorids. 

The  salt  obtained  under  the  above  mentioned  conditions  seems 
to  be  the  normal  phosphate,  A1PO4. 

Effect  of  Iron  Salts. — Five  grams  of  ammonium  ferric  alum 
dissolved  in  water,  two  grams  of  ammonium  phosphate  added, 
and  treated  as  for  aluminum  phosphate,  precipitating  while  slight- 
ly warm,  washing  20  times  with  ammonium  nitrate,  gave  an- 


ESTIMATION  OF  ALUMINA  AND  FERRIC  OXID  257 

average  of  1.2  milligrams  of  alumina.  The  iron,  therefore,  has 
a  slightly  disturbing  effect  when  present  in  large  quantities. 

Solutions  containing  aluminum  sulfate,  ammonium  phosphate 
and  five  grams  of  ammonio-ferric  alum  yielded  apparently  larger 
quantities  of  alumina,  by  the  usual  methods,  than  the  theoretical 
amount.  When  these  solutions,  however,  were  previously  treated 
with  thiosulfate  the  theoretical  amounts  of  alumina  were  ob- 
tained. 

Effect  of  Calcium  Salts. — The  presence  of  calcium  salts  pro- 
duces even  less  disturbance  in  the  results  than  iron  compounds. 
The  addition  of  two  grams  of  calcium  phosphate  gave  no  indi- 
cation of  alumina  in  the  final  results.  When  aluminum  phos- 
phate was  present  in  the  same  quantity  as  the  calcium  salt,  the 
theoretical  yield  of  alumina  was  74.3  milligrams  instead  of  70.5 
milligrams,  doubtless  due  to  the  mechanical  entanglement  of  other 
compounds.  When  a  second  precipitation  was  employed,  this  error 
disappeared.  There  was  obtained  an  average  of  31.5  milligrams 
of  alumina  where  the  theoretical  yield  was  31.9  milligrams. 

From  the  foregoing  results  the  conclusion  seems  warranted 
that  aluminum  phosphate  can  be  quantitatively  separated  by  a 
soluble  thiosulfate  and  ammonium  chlorid  reagent  from  a  hydro- 
chloric acid  solution  of  iron,  alumina,  and  lime  phosphates  con- 
taining only  a  small  amount  of  sulfates.  The  statement  of  many 
observers,  that  theoretical  results  on  aluminum  phosphates  can 
only  be  obtained  in  the  presence  of  an  excess  of  phosphoric  acid, 
has  been  confirmed.  The  error  produced  by  precipitating  a  sec- 
ond time  without  adding  phosphoric  acid  amounted  in  some  cases 
to  two  milligrams  alumina. 

The  Effect  of  Magnesium,  Sodium  and  Potassium  Salts. — Salts 
of  sodium,  magnesium  and  potassium  were  added  to  the  solutions 
containing  alumina  before  precipitation  as  phosphate,  and  it  was 
found  that  they  exerted  no  disturbing  influence  on  the  results 
obtained. 

The  Effect  of  Sulfates. — In  these  cases  the  removal  of  silica 
is  necessary  and  the  property  of  the  insolubility  of  silica  in  sul- 
furic  acid  was  used  as  the  basis  of  separation.  The  method  of 
9 


258  AGRICULTURAL  ANALYSIS 

Drown  was  employed.18  While  the  separation  of  silica  by  this 
method  is  satisfactory,  it  was  found  impossible  to  completely 
precipitate  the  aluminum  phosphate  in  the  presence  of  a  thiosul- 
fate. 

The  presence  of  more  than  1.25  grams  of  sulfuric  acid  pre- 
vents the  complete  precipitation  of  aluminum  phosphate,  while 
2.75  grams  give  a  decided  error. 

The  Effect  of  Fluorin. — The  presence  of  a  fluorid  in  a  solution 
from  which  it  is  attempted  to  separate  aluminum  by  this  method, 
is  as  disastrous  to  the  results  as  is  the  presence  of  sulfates. 

In  none  of  the  current  methods  is  the  presence  of  fluorin  men- 
tioned as  a  disturbing  factor. 

The  work  so  far  done  shows  that  alumina  can  be  quantita- 
tively separated  as  phosphate  from  a  hydrochloric  acid  solution 
containing  aluminum,  iron,  manganese,  lime,  magnesium,  sodium 
and  potassium,  when  only  small  quantities  of  sulfate  are  pres- 
ent ;  ,that  the  presence  of  silica  in  the  solution  produces  a  plus 
error  too  large  to  be  neglected ;  and  that  the  presence  of  large 
quantities  of  sulfates  or  the  presence  of  fluorids  prevents  the 
complete  precipitation  of  aluminum  phosphate.  Therefore,  to 
obtain  accurate  results,  silica  and  fluorin  must  be  removed  while 
sulfates,  not  more  than  the  equivalent  of  1.25  grams  of  sulfuric 
acid,  may  be  present. 

Proposed  Method. — The  following  method  for  estimating  alum- 
ina in  phosphates  is  based  upon  the  results  of  these  experiments : 
Treat  one  gram  of  the  substance  in  a  platinum  dish  with  from 
five  to  10  cubic  centimeters  of  hydrofluoric  acid,  let  stand  in  the 
cold  from  two  or  three  hours,  heat  on  the  water  bath  to  com- 
plete dryness,  add  two  cubic  centimeters  of  concentrated  sulfuric 
acid,  running  well  around  the  sides,  and  heat  at  a  low  tempera- 
ture until  the  substance  no  longer  flows  in  the  dish.  By  this 
process  fluorin  is  completely  expelled.  Cool  and  add  from  10 
to  20  cubic  centimeters  of  concentrated  hydrochloric  acid,  and 
warm  a  few  minutes  to  soften  the  mass ;  transfer  to  a  small 
beaker,  and  boil  until  all  aluminum  compounds  are  surely  dis- 
solved (from  15  to  30  minutes)  ;  filter  from  undissolved  residue, 

18  Transact'ons  of  the  American  Institute  of  Mining  Engineers,  1878-79, 
7  :  346. 


GENERAL    CONCLUSIONS  259 

if  any,  washing  the  filter  thoroughly,  add  50  cubic  centimeters  of 
25  per  cent,  ammonium  chlorid  solution  and  ammonia  until  alka- 
line, then  hydrochloric  acid  until  the  precipitate  just  dissolves. 
Cool,  dilute  to  about  250  cubic  centimeters,  and  add  50  per  cent, 
sodium  thiosulfate  solution,  drop  by  drop,  until  the  solution  is 
colorless,  adding  in  all  20  cubic  centimeters ;  cover  with  a  watch- 
glass,  boil  half  an  hour,  filter,  wash  back  into  the  same  beaker, 
and  dissolve  in  boiling  hydrochloric  acid;  reprecipitate  exactly 
as  before,  after  adding  two  cubic  centimeters  of  a  10  per 
cent,  ammonium  phosphate  solution.  Wash  20  times  with  five 
per  cent,  ammonium  nitrate  solution,  and  ignite  to  constant 
weight.  For  the  second  precipitation  ammonium  thiosulfate  may 
also  be  used,  but  it  is  not  necessary. 

The  greatest  difficulty  to  be  overcome  in  the  execution  of 
this  method  in  the  case  of  natural  phosphates  is  the  error  pro- 
duced by  the  presence  of  fluorin;  hence  it  is  necessary  to  heat 
the  substance  for  a  long  time  with  sulfuric  acid  to  insure  the 
complete  removal  of  fluorin  before  beginning  the  separation  of 
the  aluminum  phosphate. 

An  attempt  to  overcome  this  source  of  error  by  adding  an 
alkaline  acetate  before  boiling  with  thiosulfate  gave  no  satisfac- 
tory result. 

Estimation  of  Ferric  Oxid. — The  determination  of  ferric  oxid 
is  made  as  follows:  Dissolve  one  gram  of  the  substance  in  20 
cubic  centimeters  of  sulfuric  acid,  dilute,  filter,  washing  the  filter 
thoroughly,  and  if  any  organic  matter  is  present  add  a  little  potas- 
sium chlorate  and  boil  until  chlorin  is  expelled.  Reduce  the  iron 
with  zinc,  filter,  and  titrate  at  once  with  potassium  permanganate 
solution,  one  cubic  centimeter  of  which  equals  0.0025  gram  of 
ferric  oxid. 

222.  Separation  of  Alumina  from  Iron  by  Phenylhydrazine. — 
This  method  of  separation  was  proposed  by  Hess  and  Campbell 
and  elaborated  by  Allen.19     It  is  based  on  the  reduction  of  the 
iron  by  a  sulfite  and  the  precipitation  of  the  alumina  by  phenyl- 
hydrazine. 

223.  General  Conclusions. — It   is   evident   from  the   foregoing 

19  Journal  of  the  American  Chemical  Society,  1899,  21  :  776. 
Journal  of  the  American  Chemical  Society,  1903,  25  :  421. 


20O  AGRICULTURAL  ANALYSIS 

that  many  difficulties  beset  the  separation  of  iron  and  alumina 
from  the  other  substances  occurring  in  phosphatic  deposits.  Veitch 
has  called  especial  attention  to  these  difficulties  in  view  of  the 
persistence  with  which  ordinary  precautions  are  disregarded.20 
The  important  points  to  be  kept  in  view  are  that  all  the  iron 
should  be  in  solution  in  the  ferric  state,  the  solution  should  be  free 
of  silica,  and  should  contain  no  more  than  0.5  gram  substance  in 
300  cubic  centimeters.  In  these  conditions  the  precipi- 
tation of  the  phosphates  of  iron  and  alumina  is  made  in  a  five 
per  cent,  solution  of  ammonium  chlorid,  and  the  precipitate  after 
washing  several  times  with  hot  water,  is  dissolved  in  hydrochloric 
acid  diluted  to  about  300  cubic  centimeters  and  reprecipitated  as 
before,  with  care  to  have  always  an  excess  of  phosphoric  acid 
over  the  amount  required  to  unite  with  all  the  iron  and  alumina 
present.  The  precipitate  is  washed  free  of  chlorid  with  a  five 
per  cent,  ammonium  nitrate  solution  and  ignited  to  constant 
weight.  With  the  precautions  noted,  concordant  results  may  be 
obtained  by  precipitating  with  ammonium  acetate  and  determining 
the  phosphates  thrown  out.  The  aluminum  may  be  separated 
from  the  iron  with  thiosulfate  of  ammonium  or  sodium,  as  pointed 
out  by  Veitch.21  The  iron  may  afterwards  be  determined  by 
titration. 

The  iron  may  be  determined  separately  by  reduction  to  the 
ferrous  state  and  oxidizing  by  potassium  permanganate  or  bi- 
chromate. 

The  solutions  must  in  all  cases  be  free  of  organic  matter.  If 
manganese  titanium  or  vanadium  be  present  the  accuracy  of  the 
iron  determination  will  be  affected,  and  these  elements  must  be 
separately  determined  where  extreme  accuracy  is  desired.  The 
small  quantities  of  these  bodies  usually  found,  although  they  deport 
themselves  in  the  presence  of  phosphoric  acid  much  in  the  same 
way  as  iron,  do  not  introduce  any  material  error  into  the  per- 
centage determination  when  weighed  as  iron  phosphate,  because 
they  have  approximately  the  same  atomic  weight  as  iron  itself. 

224.  Estimation  of  Sulfuric  Acid. — As  a  rule,  sulfates  are  not 
20  Proceedings  of  the  Fifth  International  Congress  of  Applied  Chemis- 
try, Berlin,  1903,  1  :  492. 

.*l  Journal  of  the  American  Chemical  Society,  1900,  22  :  246. 


SIGNIFICATION  OF  FLUORIN  26 1 

abundant  in  mineral  phosphates.  In  case  the  samples  are  pyritif- 
erous,  however,  considerable  quantities  of  sulfuric  acid  may  be 
found  after  treatment  with  aqua  regia. 

The  acid  is  precipitated  with  barium  chlorid,  in  the  usual  way, 
in  an  aliquot  portion  of  the  filtrate  first  obtained.  The  precipi- 
tate of  barium  sulfate  is  washed  with  hot  water  until  clean,  dried, 
ignited,  and  weighed.  If  the  portion  of  the  filtrate  used  repre- 
sents half  a  gram  of  the  original  material,  then  the  weight  of 
barium  sulfate  obtained  multiplied  by  0.6858  will  give  the  quan- 
tity of  sulfur  trioxid  in  one  gram. 

OCCURRENCE  OF  FLUORIN  IN  PHOSPHATES 

225.  Signification  of  Fluorin. — Fluorin  is  quite  a  constant  con- 
stituent of  organic  phosphates  of  lime,  as,  for  instance,  bones  and 
teeth,  and  occurs  in  considerable  quantities  in  many  deposits  of 
such  phosphates  used  for  commercial  purposes.  It  is  the  cause 
of  much  discomfort  and  annoyance  in  fertilizer  factories. 

The  phosphates  of  pure  mineral  origin,  and  also  sedimentary 
phosphates,  contain  uniformly  considerable  quantities  of  fluorin, 
in  fact,  in  quite  a  definite  proportion,  and  generally  correspond 
in  composition  to  apatite.  Under  the  influence  of  living  organs, 
of  plants  and  animals,  the  fluorin  tends  to  disappear.22 

The  exact  determination  of  fluorin,  therefore,  in  phosphates,  is 
of  more  than  usual  interest  because  its  amount  will  throw  much 
light  on  the  origin  of  the  sample  under  examination. 

Free  coproliths,  that  is,  nodules  of  organic  phosphates,  are 
very  rarely  found.  What  are  so  called,  preserve  only  the  form. 
The  original  materials  have  been  replaced  by  the  fluoi  phosphates 
of  more  distinctly  mineral  nature.  The  fossil  bones  sometimes 
found  in  sedimentary  phosphate  deposits  are  only  bones  in  form, 
just  as  fossil  trees  are  only  so  in  form.  The  analysis  of  the 
phosphatic  material  composing  them  shows  them  to  be  different 
from  true  bone.  Only  fossil  phosphates  unmetamorphosed  exist 
in  recent  geological  epochs  and  in  guano  deposits. 

The  almost  universal  presence  of  fluorin  in  natural  phosphates 
makes  of  especial  interest  the  methods  for  its  exact  estimation. 
The  presence  of  fluorin  is  of  little  consequence  from  a  practical 
«  Lasne,  L'Engrais,  1896,  11  :  1145,  1168. 


262  AGRICULTURAL  ANALYSIS 

point  of  view,  except  in  the  decomposition  of  phosphates  with 
sulfuric  acid,  where  the  evolution  of  hydrofluoric  acid  or  hydro- 
fluosilicic  acid  may  cause  grave  inconvenience  to  the  workman 
and  damage  to  the  apparatus.  It  is  important  to  know  the  exact 
content  of  a  phosphate  in  fluorin  before  submitting  it  to  the  pro- 
cess of  manufacture,  by  means  of  which  phosphoric  acid  is  ren- 
dered soluble  in  water  and  ammonium  citrate.  The  principles 
upon  which  the  estimation  of  the  fluorin  depend,  comprise  both 
the  decomposition  of  the  substance  by  fusion  with  the  carbonate 
of  soda  and  silica,  and  the  estimation  of  the  fluorin  in  the 
hydrofluosilicic  acid  evolved  by  the  simultaneous  action  of  con- 
centrated sulfuric  acid  and  silica  upon  the  fluorin  compound.  The 
last  method  theoretically  leads  to  the  realization  of  the  conditions 
necessary  for  an  exact  determination,  but  in  practice  it  has  been 
found  to  be  attended  with  very  great  difficulties.  The  assump- 
tion that  the  hydrofluosilicic  acid  is  evolved  in  the  pure  state  is 
wot  always  correct,  since  phosphates  contain  quite  commonly 
some  carbonates  and  organic  matters,  and  even  chlorids.  When 
these  compounds  are  treated  with  concentrated  sulfuric  acid,  there 
is  set  free  some  sulfurous,  carbonic,  and  hydrochloric  acids,  and 
these  escaping  in  a  gaseous  form,  are  likely  to  carry  with  them 
also  some  water  vapor.  In  the  application  of  this  method  it  has 
therefore  been  found  necessary  to  previously  ignite  the  phosphate, 
and  this  operation  is  also  open  to  objections.  In  case  calcination 
is  practiced,  it  is  necessary  to  carry  it  so  far  that  there  remains 
no  trace  of  carbonic  acid,  or  of  carbon,  for  the  presence  of  these 
bodies  would  interfere  seriously  with  the  subsequent  determina- 
tion of  the  fluorin.  Even  when  this  method  can  be  successfully 
practiced  with  natural  phosphates,  it  will  be  found  extremely  diffi- 
cult of  application  in  the  estimation  of  any  residual  fluorin  in 
superphosphates. 

226.  Estimation  of  Fluorin  by  the  Method  of  Berzelius  as 
Modified  by  Chatard. — The  method  of  estimating  fluorin  as  pro- 
posed by  Berzelius  has  been  found  quite  satisfactory  in  the  labo- 
ratory of  the  Geological  Survey,  with  the  modifications  given  be- 
low.28 

M  Transactions  of  the  American  Institute  of  Mining  Engineers,  1892-93, 
21  :  170. 


ESTIMATION  OF  FLUORIN  263 

Two  grams  of  the  phosphate  are  intimately  mixed  in  a  large 
platinum  crucible  with  three  grams  of  precipitated  silica  and  12 
grams  of  pure  sodium  carbonate,  and  the  mixture  is  gradually 
brought  to  clear  fusion  over  the  blast-lamp.  When  the  fusion 
is  complete  the  melt  is  spread  over  the  walls  of  the  crucible, 
which  is  then  rapidly  cooled  (preferably  by  a  blast  of  air).  If 
this  has  been  properly  done,  the  mass  separates  easily  from  the 
crucible,  and  the  subsequent  leaching  is  hastened.  The  mass, 
detached  from  the  crucible,  is  put  into  a  platinum  dish  into  which 
whatever  remains  adhering  to  the  crucible  or  its  lid  is  also  washed 
with  hot  water.  A  reasonable  amount  of  hot  water  is  now  put 
into  the  dish,  which  is  covered  and  digested  on  the  water  bath 
until  the  mass  is  thoroughly  disintegrated.  To  hasten  this,  the 
supernatant  liquid  may,  after  a  while,  be  poured  off,  the  residue 
being  washed  into  a  small  porcelain  mortar,  ground  up,  returned 
to  the  dish  and  boiled  with  fresh  water  until  no  hard  grains  are 
left.  The  total  liquid  is  filtered,  and  the  residue  is  washed  with 
hot  water.  The  filtrate  (which  should  amount  to  about  half  a 
liter)  is  nearly  neutralized  with  nitric  acid  (methyl  orange  being 
used  as  indicator),  some  pure  sodium  bicarbonate  is  at  once 
added,  and  the  solution  (in  a  platinum  dish,  if  one  large  enough 
is  at  disposal,  otherwise  in  a  beaker)  is  placed  on  the  water 
bath,  when  it  speedily  becomes  turbid  through  separation  of 
silica.  As  soon  as  the  solution  is  warm  it  is  removed  from  the 
bath,  stirred,  allowed  to  stand  for  two  or  three  hours,  and  then 
filtered  by  means  of  the  filter-pump  and  washed  with  cold  water. 

The  filtrate  is  concentrated  to  about  a  quarter  of  a  liter  and 
nearly  neutralized,  as  before,  some  sodium  carbonate  is  added, 
and  the  phosphoric  acid  is  precipitated  with  silver  nitrate  in 
excess.  The  precipitate  is  separated  by  filtration  and  washed 
with  hot  water,  and  the  excess  of  silver  in  the  filtrate  is  removed 
with  sodium  chlorid. 

The  filtrate  from  the  silver  chlorid  (after  addition  of  some 
sodium  bicarbonate)  is  evaporated  to  its  crystallizing  point,  then 
cooled  and  diluted  with  cold  water ;  still  more  sodium  bicarbon- 
ate is  added,  and  the  whole  is  allowed  to  stand,  when  additional 
silica  will  separate,  and  this  is  to  be  removed  by  filtration. 

This  final  solution  is  nearly  neutralized,   as  before;   a  little 


264  AGRICULTURAL  ANALYSIS 

sodium  carbonate  solution  is  added;  it  is  heated  to  boiling  and 
an  excess  of  solution  of  calcium  chlorid  is  added.  The  precipi- 
tate of  calcium  fluorid  and  carbonate  must  be  boiled  for  a  few 
minutes,  when  it  can  be  easily  filtered  and  washed  with  hot 
water.  The  precipitate  is  then  washed  from  the  filter  into  a 
small  platinum  dish  and  evaporated  to  dryness,  while  the  filter, 
after  being  partially  dried  and  used  to  wipe  off  any  particles  of 
the  precipitate  adhering  to  the  dish  in  which  it  was  formed,  is 
burned,  and  the  ash  is  added  to  the  main  precipitate.  This, 
when  dry,  is  ignited,  and  allowed  to  cool ;  dilute  acetic  acid  is 
added  in  excess,  and  the  whole  is  evaporated  to  dryness,  being 
kept  on  the  water  bath  until  all  odor  of  acetic  acid  has  disap- 
peared. The  residue  is  then  treated  with  hot  water,  digested, 
filtered  on  a  small  filter,  washed  with  hot  water,  partially  dried 
put  into  a  crucible,  carefully  ignited,  and  weighed  as  calcium 
fluorid.  The  calcium  fluorid  is  then  dissolved  in  sulfuric  acid 
by  gentle  heating  and  agitation,  evaporated  to  dryness  on  a 
radiator,  ignited  at  full  red  heat,  and  weighed  as  calcium  sulfate. 
From  this  weight  the  equivalent  weight  of  calcium  fluorid  should 
be  calculated,  and  this  should  be  very  close  to  that  actually 
found  as  above,  but  should  never  exceed  it.  The  difference 
which  is  generally  about  a  milligram  (sometimes  more),  is  due 
to  silica  precipitated  with  the  fluorid.  The  percentage  of  fluorin 
is,  therefore,  always  calculated  from  the  weight  of  the  sulfate. 
and  not  from  that  of  the  fluorid  obtained. 

The  main  improvements  in  this  method  are  the  use  of  sodium 
bicarbonate  to  separate  the  silica,  and  the  keeping  of  the  earlier 
solutions  as  dilute  as  possible,  which  can  not  be  done  if  ammo- 
nium carbonate  be  used  for  the  separation  of  the  silica.  These 
changes  make  the  fluorin  estimation,  although  still  tedious,  far 
more  rapid  than  before,  and  the  results  are  very  satisfactory. 

227.  Modification  of  Wyatt. — By  reason  of  the  tediousness  of 
the  method  of  Chatard  given  above,  Wyatt  has  sought  to  shorten 
the  process  by  the  following  modification.24 

The  presence  of  fluorin  having  been  established  by  a  qualita- 
tive test,  its  estimation  is  secured  as  follows : 
24  Phosphates  of  America,  4th  Edition,  1892  :  149. 


MODIFICATION   OF   WYATT  265 

Five  grams  of  the  finely  ground  phosphate  are  fused  in  a 
platinum  dish  with  15  grams  of  the  mixed  carbonates  of  sodium 
and  potassium  and  two  grams  of  very  fine  sand.  After  fusing 
very  thoroughly  with  a  strong  heat  for  a  quarter  of  an  hour,  the 
dish  is  removed  from  the  fire  and  cooled.  Its  contents,  dis- 
solved in  hot  water,  are  then  put  into  a  half-liter  flask,  and  a 
considerable  excess  of  ammonium  carbonate  is  added  to  the 
liquid.  All  the  soluble  silica  falls  out  of  solution,  and  the  flask, 
after  cooling,  is  made  up  to  the  mark  with  distilled  water,  well 
shaken,  and  then  set  aside  for  24  hours  to  settle.  At  the  end 
of  this  time  200  cubic  centimeters  are  carefully  decanted  through 
a  filter;  the  filter  is  well  washed,  and  the  filtrate,  after  being 
nearly  neutralized  with  hydrochloric  acid,  is  treated  with  an 
excess  of  calcium  chlorid  solution. 

The  precipitate,  consisting  of  phosphate,  fluorid,  and  some 
calcium  carbonate,  is  allowed  to  settle,  and  is  then  carefully 
washed  with  boiling  water,  first  by  decantation  several  times, 
and  finally  on  the  filter.  After  being  properly  dried  in  the  gas- 
oven,  calcined,  and  cooled,  the  residue  is  treated  with  acetic 
acid,  placed  upon  the  water-bath,  and  evaporated  to  complete 
ilryness. 

The  calcium  acetate  is  now  well  washed  out  by  several  treat- 
ments with  boiling  water,  and  the  residue  is  brought  upon  a 
filter,  dried,  calcined,  and  weighed.  The  weight  represents  the 
calcium  phosphate  and  fluorid  contained  in  two  grams  of  the 
original  sample;  and  if  the  calcium  phosphate  in  the  residue 
"be  determined  according  to  the  usual  methods,  the  difference  will 
be  calcium  fluorid  and  may  be  thus  estimated. 

For  this  purpose  the  mixed  phosphate  and  fluorid  is  placed  in 
a  platinum  dish  and  the  fluorin  expelled  by  treatment  with  sul- 
furic  acid.  The  residue  is  taken  up  with  alcohol,  100  cubic  cen- 
timeters, the  undissolved  portion  washed  with  an  additional  100 
cubic  centimeters  of  alcohol,  and  the  phosphoric  acid  determined 
in  the  alcoholic  solution  by  precipitation  as  ammonio-magnesium 
phosphate. 

Example. — Assuming  the  calcined  residue  of  calcium  phos- 
phate and  fluorid  in  two  grams  of  the  original  sample  to  have 


266  AGRICULTURAL  ANALYSIS 

amounted  to  1.6  gram  and  the  calcium  phosphate  in  this  quan- 
tity to  have  been  determined  as  1.540  gram,  the  calcium  fluorid  is 
thus  proved  to  be  0.060  gram,  and,  therefore,  2:0.060:  :ioo:x= 3 
per  cent,  calcium  fluorid,  which,  multiplied  by  0.4897,  gives  1.46 
per  cent,  of  fluorin. 

The  above  method,  while  shorter,  is  not  to  be  preferred  to  the 
former  process  when  great  accuracy  is  desired.  All  the  solu- 
ble silica  may  not  fall  out  of  the  solution  as  Wyatt  says.  Again, 
the  method  of  separating  the  phosphoric  acid  can  not  be  regarded 
as  strictly  accurate.  Finally,  the  fluorin  is  calculated  from  small 
differences  in  the  weight  of  very  heavy  precipitates,  and  all  the 
error  of  the  process  may  be  found  affecting  the  numbers  for 
fluorin.  For  commercial  purposes,  however,  the  method  has  the 
merit  of  comparative  brevity. 

228.  Method  of  Rose. — Clarke  and  Hillebrand  recommend 
the  Rose  modification  of  the  method  just  described,  in  which 
chromium  and  any  residue  of  phosphoric  acid  are  removed  by 
silver  nitrate.*5  The  previous  separation  of  silica  and  alumina  by 
carbonate  of  ammonium  is  advised  instead  of  nitrate  or  chlorid,  to 
avoid  loss  of  fluorin  on  evaporation.  By  whatever  method  the 
silica  is  thrown  out,  the  alkaline  carbonate  must  be  converted 
into  nitrate  and  not  chlorid  if  chromium  and  phosphorus  are 
present.  The  solution  at  the  time  the  silver  nitrate  is  added 
should  contain  enough  of  undecomposed  alkaline  carbonate  to 
cause  a  copious  precipitation  of  silver  carbonate  in  order  to  take 
up  the  acid  set  free.  After  heating  and  filtering  the  excess  of 
silver  is  to  be  removed  by  sodium  or  potassium  chlorid,  sodium 
carbonate  added,  and  the  fluorin  precipitated  by  calcium  chlorid 
in  excess.  No  ammonium  salts  should  be  present  in  the  solution 
when  the  calcium  chlorid  is  added,  for  these  tend  to  hold  the 
fluorin  in  solution.  The  remaining  part  of  the  operation  is  con- 
ducted as  above  described.  Attention  is  called  to  the  fact  that 
there  is  no  very  satisfactory  qualitative  test  for  the  presence  of 
fluorin.  The  usual  method  of  heating  the  powdered  substance  by 
the  blowpipe,  with  sodium  metaphosphate  on  platinum  foil,  is 
not  always  reliable. 

74  U.  S.  Geological  Survey,  Bulletin  148,  1897  :  57. 


METHOD  OF  LASNE  267 

229.  Burk's  Modification  of  Carnot's  Method. — Carnot's  method 
is  based  on  the  digestion  of  a  substance  containing  silica  and  a 
fluorid  with  sulfuric  acid  and  conducting  the  silicon  tetrafluorid 
evolved   into  a  solution  of  potassium  fluorid.20     The   reactions 
which  take  place  are  expressed  by  the  following  formulas : 

1.  CaF2  +  H,SO4  =  2HF  +  CaSO4. 

2.  4HF+  Si62  =  SiF4  +  2H2O. 

3.  SiF4  +  2KF  =  K2SiFc. 

The  potassium  fluosilicate  separates  in  part  and  is  completely 
precipitated  by  90  per  cent,  alcohol.  After  standing,  the  precipi- 
tate is  collected  on  a  filter,  washed  free  of  potassium  fluorid  by  90 
per  cent,  alcohol,  and  dried  to  constant  weight. 

Two-thirds  of  the  fluorin  in  the  dried  product  is  derived  from 
the  mineral  under  investigation.  The  number  representing  the 
weight  of  the  precipitate  multiplied  by  0.34511  gives  the  fluorin, 
and  this  multiplied  by  2.0527  gives  the  weight  of  the  calcium 
fluorid  corresponding  thereto.  Burk  describes  the  apparatus  suited 
to  the  conduct  of  the  work,  and  states  the  conditions  under  which 
it  is  accurate.27  The  chief  sources  of  error  are: 

1.  Moisture  in  the  air  or  tubes  through  which  the  silicon  tetra- 
fluorid passes. 

2.  Fumes  of  sulfuric  acid  carried  over  in  the  air  current  or 
otherwise. 

3.  Insoluble  addition  products  of  potassium  fluorid  with  the 
silica  of  the  glass. 

The  methods  of  avoiding  these  sources  of  error  are  set  forth 
in  detail  in  the  paper  cited  above. 

230.  Method  of  Lasne. — The  difficulties  which  have  been  men- 
tioned led  Lasne  to  modify  the  method  of  separating  the  hydro- 
fiuosilicic  acid  in  such  a  way  as  to  render  it  practicable  and 
exact.28 

The  modification  of  Lasne  consists  essentially  in  removing  the 
hydrofluosilicic  acid  evolved  by  the  action  of  concentrated  sul- 
furic acid  on  natural  phosphate  by  a  current  of  dry  air  conducted 

26  Comptes  rendus,  1892,  114  :  75°,  1003. 

27  Journal  of  the  American  Chemical  Society,  1901,  23  :  825. 

m  Bulletin  de  la  Socie'te'   chimique  de  Paris,    1888,    [2],  50  :  167. 
Annales  de  Chimie  analytique,  1897,  2  :  161,  182. 


268 


AGRICULTURAL  ANALYSIS 


into  a  solution  of  caustic  soda,  where  the  fluorin  is  retained  and 
ultimately  estimated.  It  does  not  matter  that  the  fluorin  in  this 
case  is  accompanied  with  other  gases,  and  with  vapor  of  water, 
since  these  impurities  are  absolutely  without  inconvenience  in 
the  subsequent  proceedings.  The  phosphates  can  be  treated  with- 
out previous  calcination  or  preparation  in  any  form,  and  after 
mixing  with  sulfuric  acid  the  temperature  can  be  raised  just  to 


Dry  a  i 


Aapircctor 


Fig.  12.     l.asnc's  Apparatus. 

the  point  of  ebullition,  which  promotes  very  greatly  the  speed 
of  the  reaction  and  the  perfect  separation  of  the  fluorin.  The 
operation  is  conducted  as  follows: 

A  definite  quantity  of  the  phosphate  or  any  other  body  what- 
ever containing  fluorin,  provided  it  be  decomposable  by  sulfuric 
acid,  is  introduced  into  a  dry  flask  in  which  have  been  previously 
placed  about  50  cubic  centimeters  of  strong  sulfuric  acid  and  10 
grams  of  finely  ground  sand.  The  quantity  of  the  phosphate  em- 
ployed should  be  such  as  to  secure,  if  possible,  an  amount  con- 
taining o.i  gram  of  calcium  fluorid.  In  phosphates  which  are 
very  poor  in  fluorin  it  will  be  necessary  to  use  from  10  to  20 
grams.  One  of  the  great  advantages  of  this  process  lies  in  the  fact 
that  it  permits  the  employment  of  these  great  quantities  of 
materials  without  in  any  way  interfering  with  the  accuracy  of 
the  analysis.  The  flask  and  receiving  bottles  employed  in  the 


METHOD  OF  LASNE  269 

operation  are  illustrated  by  the  accompanying  Figure  12.  The  first 
receiving  flask  (B)  contains  two  and  one-half  grams  of  caustic 
soda  in  25  cubic  centimeters,  and  the  second  (C)  a  half  a  gram 
in  the  same  volume  of  water.  The  second  flask  is  connected 
with  the  aspirator,  by  means  of  which  the  current  of  air  is  drawn 
through  the  whole  apparatus.  At  the  beginning  of  the  operation 
the  current  of  dry  air  is  drawn  through  slowly  and  the  flask  (A) 
is  moderately  heated  until  its  contents  are  brought  to  near  the 
boiling  point.  During  the  heating  the  flask  should  be  frequently 
shaken  to  secure  the  even  distribution  of  the  heat  throughout 
the  mass,  and  avoid  danger  of  breakage.  In  this  condition  the 
evolution  of  the  fluorin  is  terminated  in  about  three  hours.  A 
blank  experiment  should  show  that  the  sulfuric  acid  and  sand 
employed  are  free  of  fluorin.  Sulfuric  acid  and  sand  entirely 
free  from  fluorin  may  be  easily  secured  by  heating  one  liter  of 
the  acid  for  two  or  three  hours  with  100  grams  of  finely  ground 
sand,  previously  washed  with  hydrochloric  acid.  After  cooling, 
the  acid  is  decanted  into  a  dry  glass-stoppered  flask,  and  the 
residual  sand  is  washed  and  dried.  These  reagents  are,  when 
prepared  in  this  way,  both  free  from  fluorin.  When  the  fluorid 
of  silica  is  entirely  evolved  from  the  mixture,  which  is  easily 
determined  by  observing  that  the  contents  of  the  flask  become 
limpid,  the  lamp  is  extinguished  and  the  mass  is  allowed  to  cool 
until  the  flask  can  be  easily  handled.  It  is  then  removed  and  the 
delivery  tube  washed  into  a  dish  into  which  subsequently  are 
poured  the  contents  of  the  two  receiving  flasks,  and  their  con- 
necting tubes  are  washed  with  water.  The  solution  obtained  in 
this  way  should  still  be  freely  alkaline,  as  indicated  by  forming 
a  red  color  with  phenolphthalein.  If  it  be  not  alkaline,  a  suffi- 
cient quantity  of  caustic  soda  should  be  added.  The  contents  of 
the  dish  are  heated  for  half  an  hour  to  100°  for  the  purpose  of 
decomposing  into  hydrofluoric  acid  and  silica  the  fluosilicate 
which  has  been  formed  at  first.  The  total  volume  of  the  solution, 
in  order  to  facilitate  the  operation,  should  be  reduced  by  evap- 
oration to  about  100  cubic  centimeters.  After  partial  cooling  the 
solution  is  saturated  with  carbon  dioxid,  the  flask  being  covered 
meanwhile  to  prevent  any  loss  by  the  projection  of  the  liquor 
with  the  escaping  gas.  The  residual  liquor  and  the  wash  water 


270  AGRICULTURAL  ANALYSIS 

coming  from  the  covered  dish  are  introduced  into  a  flask  grad- 
uated to  125  cubic  centimeters,  which  should  not  be  completely 
filled.  Some  solid  carbonate  of  ammonia  is  added  and  the  mix- 
ture heated  for  half  an  hour  to  about  50°,  adding  from  time  to 
time  a  little  of  the  carbonate.  By  this  process  the  silica  is,  as  a 
rule,  completely  precipitated.  Nevertheless,  as  it  is  important 
that  not  the  least  trace  of  silica  be  in  solution,  it  is  recommended 
to  finish  the  separation  with  oxid  of  zinc.  For  this  purpose  the 
volume  of  the  mixture  is  completed  to  the  mark  and  the  contents 
of  the  flask  filtered  into  a  dried  beaker.  One  hundred  cubic  cen- 
timeters of  the  filtrate  are  placed  in  a  porcelain  dish  and  10  cubic 
centimeters  of  solution  of  oxid  of  zinc  in  ammonia,  in  all  about 
0.3  gram  of  oxid  of  zinc,  are  added.  The  solution  is  evaporated 
almost  to  dryness  and  some  water  added,  and  the  evaporation 
repeated  in  this  way  two  or  three  times.  The  precipitate  of  car- 
bonate of  zinc  formed  carries  down  the  last  traces  of  silica.  The 
whole  precipitate  is  finally  collected  upon  a  filter  and  washed. 
Since  the  quantity  of  carbonate  of  soda  present  is  not  exactly 
known,  there  are  added  to  the  solution  a  few  drops  of  tropeolin, 
and  carefully,  afterwards,  diluted  hydrochloric  acid,  until  a  rose 
tint  is  produced,  and  without  waiting  10  cubic  centimeters  of  a 
solution  of  carbonate  of  soda  containing  300  grams  of  the  crys- 
tallized salt  per  liter.  This  quantity  of  carbonate  of  soda  should 
be  prepared  in  advance,  so  that  it  can  be  added  instantly,  as  it  is 
not  safe  to  leave  the  solution  acid,  because  it  will  attack  the  glass 
and  bring  a  small  quantity  of  silica  into  solution.  After  the  addi- 
tion of  the  carbonate  of  soda  solution  the  mixture  is  boiled  for  15 
minutes.  To  the  nearly  boiling  solution  there  is  added  a  slight 
excess  of  calcium  chlorid,  say  about  10  cubic  centimeters  of  a 
solution  containing  300  grams  of  the  crystallized  calcium  chlorid 
per  liter.  Stir  thoroughly  and  allow  to  settle  for  a  short  time 
and  filter  while  still  hot.  Wash  the  precipitate,  which  is  com- 
posed of  calcium  carbonate  and  calcium  fluorid.  The  precipitate 
is  dried  and  burned,  the  temperature  being  raised  with  great  cau- 
tion, so  as  to  avoid  a  partial  fusion,  a  phenomenon  which  is  pro- 
bably due  to  the  existence  of  a  fluocarbonate  which  has  not  yet 
been  isolated.  The  ignition  is  conducted  in  a  large  platinum  cruci- 


CARNOT' s  MODIFICATION  271 

ble.  The  capsule,  after  cooling,  is  covered  with  a  funnel,  and  from 
30  to  40  cubic  centimeters  of  water  are  poured  upon  the  ignited 
precipitate,  followed  by  three  cubic  centimeters  of  glacial  acetic 
acid.  After  the  evolution  of  carbon  dioxid  is  finished  the  funnel 
is  removed  and  washed,  the  residual  liquor  is  evaporated  to 
near  dryness,  water  added,  and  the  evaporation  repeated  two 
or  three  times  and  finished  by  evaporating  to  dryness.  The  res- 
idue is  taken  up  with  30  or  40  cubic  centimeters  of  water  con- 
taining one  per  cent,  of  acetic  acid.  After  heating  for  a  mo- 
ment the  fluorid  of  calcium  which  remains  insoluble  is  collected 
and  washed  with  water  slightly  acidulated  with  acetic.  The 
washing  is  finished  with  pure  water.  The  absence  of  sulfates  in 
the  last  wash  water  should  be  ascertained  by  a  careful  test.  It 
is  rather  difficult  to  filter  the  calcium  fluorid,  and  some  precau- 
tions to  avoid  a  turbid  filtrate  will  be  found  necessary.  The  pre- 
cipitate is  dried,  ignited  and  the  fluorid  of  calcium,  obtained  in  a 
perfectly  pure  state,  weighed.  The  purity  of  the  residue  can  be 
determined  by  dissolving  with  concentrated  sulfuric  acid,  after* 
wards  diluting  a  little  and  precipitating  by  alcohol.  The  sulfate 
of  lime  obtained  in  this  way  should  correspond,  molecularly,  to 
the  original  calcium  fluorid.  According  to  Lasne,  this  method, 
if  carefully  followed,  gives  results  which  are  rigorously  exact. 

231.  Carnot's  Modification. — Carnot  has  proposed  to  shorten 
the  method  of  Lasne  in  the  following  manner: 

In  place  of  receiving  the  fluorid  of  silicium  in  caustic  soda, 
the  gas  is  conducted  into  a  solution  of  fluorid  of  potash,  the 
delivery  tube  being  plunged  into  mercury  to  avoid  obstruction. 
There  is  thus  formed  a  fluosilicate,  which  is  precipitated  by 
alcohol,  collected  upon  a  tared  filter  and  weighed.  Lasne  con- 
sidered this  method  to  be,  in  fact,  more  rapid,  but  dangerous.  It 
is  always  inconvenient,  according  to  him,  to  use  in  determination 
a  body  of  the  same  nature  as  that  which  is  to  be  determined,  a 
process  which  renders  all  final  verification  impossible. 

Goutal  has  criticised  the  method  of  Lasne.  preferring  the  shorter 
method  of  Carnot  mentioned  above.29  His  objections  to  the 
method  of  Lasne  are  based  upon  the  following: 

w  Annales  de  Chimie  analytique,  1897,  2  :  401. 


2/2  AGRICULTURAL  ANALYSIS 

(1)  Five  or  six  reagents  are  required. 

(2)  Evaporations  and  ebullitions  of  alkaline  liquids  are  carried 
on  in  glass  vessels,  which  are  subject  to  attack. 

(3)  The  precipitate  weighs  only  a  few  centigrams. 

(4)  The  precipitate  is  mixed  with  silica. 

(5)  The  precipitate  is  soluble  in  the  successive  reagents  em- 
ployed. 

These  objections  are  answered  by  L,asne.30 

Lasne  admits  that  if  the  phosphates  in  which  fluorin  is  to  be 
determined  are  previously  ignited,  many  of  the  objections  to  the 
shorter  method  proposed  by  Carnot  are  removed,  but  he  fears 
that  there  is  danger  of  loss  of  fluorin,  as  well  as  of  water,  by 
calcination,  and  adds  that  the  calcination  of  phosphates,  and  more 
particularly  of  bones,-  is  an  operation  which  is  neither  easy  nor 
rapid,  if  it  be  desired  to  burn  away  the  last  traces  of  carbon. 

232.  Protection  of  Glassware  in  Working  with  Fluorin. — Carnot 
has  proposed  to  coat  the  surfaces  of  flasks  and  tubes  used  in  the 
determination  of  fluorin  with  gum-lac.31 

According  to  Carnot,  this  lacquer  protects  completely  the  glass 
from  the  action  of  the  solution  of  hydrofluoric  acid. 

233.  Fluorin  in  Bones. — According  to  Carnot,  the  deposits  of 
phosphates  have  been  formed  in  the  following  manner: 

(1)  The  accumulation  of  phosphatic  animal  debris,  etc.,  along 
the  banks  of  the  ocean  or  in  lakes  or  lagoons. 

(2)  The  impregnation  of  these  phosphates  in  the  fluorid  of  cal- 
cium contained  in  the  sea  waters.     Carnot  has  demonstrated  the 
presence  and  determined  the  proportion  of  fluorin  in  the  waters 
of  the  ocean,  and  has  shown  in  the  laboratory,  by  synthetic  ex- 
periments, the  gradual  fixation  of  fluorin  in  bony  deposits. 

The  fluorin  which  is  a  constituent  of  mineral  phos- 
phates is  probably  derived  from  bones.  According  to  the 
researches  of  Carnot,  there  is  often  a  considerable  quantity 
of  calcium  fluorid  in  bones  and  teeth.32  In  fossil  bones  very  large 
quantities  have  been  found,  reaching  as  high  as  6.21  per  cent,  of 

30  Annales  de  Chimie  analytique,  1898,  3  :  6. 

31  Annales  des  Mines,  1893,  [9],  3  :  138. 
31  Comptes  rendus,  1892,  114  :  1189. 

Annales  de  Chimie  et  de  Physique,  1855,  1  :  47. 


IODIN    Ifr    PHOSPHATES  273 

calcium  fluorid  in  a  fossil  bone  in  a  phosphate  from  the  Charles- 
ton deposits.  Gabriel  has  suggested  a  means  of  determining 
a  minimum  limit  of  fluorin  in  bones  and  teeth  by  the  develop- 
ment of  etchings  in  comparison  with  known  quantities  of  pure 
calcium  fluorid.  The  minimum  quantity  of  calcium  fluorid  neces- 
sary to  produce  a  distinct  etching,  in  known  conditions,  having 
been  determined,  the  test  is  applied  to  known  weights  of  ignited 
bone  or  teeth.  He  concludes  from  his  results  that  the  ash  of 
bones  and  teeth  often  contains  less  than  one-tenth  per  cent,  of 
fluorin.  Since,  however,  there  is  a  loss  of  fluorin  from  calcium 
fluorid  on  ignition,  the  whole  of  the  fluorin  may  not  have  been 
available  in  the  tests  described. 

234.  lodin  in  Phosphates. — The  presence  of  iodin  has  been  de- 
tected in  many  natural  phosphates  and  is  of  interest  in  the  dis- 
cussion of  the  problem  of  their  origin.83  A  sample  of  phosphate 
from  Florida  was  found  to  contain  0.014  per  cent,  of  iodin.  This 
element  has  also  been  observed  in  the  phosphates  from  other  lo- 
calities, as  has  been  shown  by  Gilbert.  A  qualitative  test  for 
the  detection  of  iodin  may  be  applied  in  the  following  manner : 
Some  finely  ground  phosphate  is  mixed  with  strong  sulfuric  acid 
and  the  gases  arising  from  the  reaction  are  aspired  into  some 
carbon  disulfid  or  chloroform.  The  violet  coloration  arising 
indicates  the  presence  of  iodin.  The  gases  carrying  the  iodin 
may  also  be  brought  into  contact  with  starch-paste  producing 
the  well  known  blue  color. 

The  quantity  of  iodin  present  in  a  phosphate  is  rarely  more 
than  one  or  two-tenths  of  one  per  cent.  It  can  be  determined  as 
a  silver  salt,  in  the  absence  of  chlorin  or  by  any  of  the  standard 
methods  found  in  works  on  quantitative  analysis. 

Iodin  is  quite  a  constant  constituent  of  Florida  phosphates. 
For  a  quantitative  determination,  the  sample  is  treated  with  an 
excess  of  strong  sulfuric  acid  in  a  closed  flask  and  during  the 
decomposition  a  stream  of  air  is  aspired  through  the  flask  and 
caused  to  bubble  through  absorption  bulbs  containing  sodium  or 
potassium  hydroxid  in  solution. 

The  temperature  of  the  decomposition  may  be  raised  to  about 
200°.  After  the  distillation  is  complete  the  sodium  iodid  formed 
81  L'Engrais,  1895,  10  :  65. 


274  AGRICULTURAL   ANALYSIS 

is  titrated  by  treating  with  potassium  permanganate.3*  The  reac- 
tion is  represented  by  the  equation :  NaI-|-2KMnO4-|-H2O— 
NaIO3H-2KOH-}-2MnO2.  The  iodin  also  may  be  set  free  and 
determined  in  the  usual  way  by  titration  with  standard  sodium 
thiosulfate  solution. 

The  titration  of  free  iodin  is  represented  by  the  following  re- 
action : 

2Na2S2O8+2l=2NaI+Na2S4O6. 

In  this  reaction  thiosulfuric  acid  is  converted  into  tetrathionic 
acid  and  the  free  iodin  into  hydriodic  acid,  both  of  which  com- 
bine with  the  sodium  present.  The  decinormal  solution  of  sodium 
thiosulfate  may  be  used.  Grind  the  crystals  of  the  salt  to  a  fine 
powder,  dry  between  blotting  papers,  and  use  24.8  grams  of  the 
dried  salt  per  liter.  The  quantity  of  iodin  found  in  phosphates 
is  so  minute  that  it  is  hardly  worth  while  to  make  a  quantitative 
determination  of  it. 

235.  Occurrence  of  Chromium  in  Phosphates. — In  some  phos- 
phates  a   small   quantity  of  chromium   has   been   found.     In   a 
sample  of  phosphate  from  the  Island  of  Los  Roques  in  the  Car- 
ibbean Sea,  Gilbert  found  three-fourths  per  cent,  of  chromium 
oxid    (Cr,O3).     The   phosphates   containing   chromium   have   a 
greenish  color  and  are  characterized  by  great  insolubility  in  solu- 
tions containing  organic  acids.     The  chromium  is  to  be  deter- 
mined by  the  usual  methods  described  in  mineral  analysis. 

236.  Estimation   of  Vanadium. — In   the   complete    analysis   of 
basic  slags  it  becomes  necessary  to  determine  the  presence  of 
vanadic  mixture  with  this  solution  until  a  drop  of  the  clear  liquor, 
the  volumetric  process  of  Lindemann.35     It  is  conducted  as  fol- 
lows :     Dissolve  four  grams  of  the  finely  powdered  slag  in  60  cub- 
ic centimeters  of  dilute  sulfuric  acid  (i  14),  boil  for  a  few  min- 
utes, cool,  make  the  volume  up  to  100  cubic  centimeters,  filter  and 
add  decinormal  potassium  permanganate  solution  in  slight  excess 
to  an  aliquot  part  of  the  filtrate  to  secure  the  oxidation  of  the  vana- 
dium to  vanadium  pentoxid.   Add,  drop  by  drop,  a  weak  solution 
of  ferrous  sulfate  until  the  pink  color  just  disappears.     Prepare 

34  Sutton,  Volumetric  Analysis,  gth  Edition,  1904  :  219. 
36  Ueber  die  quantitative  Bestimmung  des  Vanadins  in  Eisenerzen,  1878. 
Zeitschrift  fiiranalytische  Chemie,  1879,  18  :  99. 


ESTIMATION    OF   VANADIUM  275 

a  ferrous  sulfate  solution  by  dissolving  2.183  grams  of  piano  wire 
in  sulfuric  acid  and  making  the  volume  to  one  liter.  Titrate  the 
vanadic  mixture  with  this  solution  until  a  drop  of  the  clear  liquor, 
removed  and  brought  in  contact  with  potassium  ferricyanid,  shows 
a  distinctive  blue-green  color. 

One  cubic  centimeter  of  the  ferrous  sulfate  solution  is  equiva- 
lent to  0.002  gram  of  vanadium,  0.002888  gram  of  vanadium  di- 
oxid,  and  0.003648  gram  of  vanadium  pentoxid.  The  ferrous 
sulfate  solution  may  also  be  made  and  standardized  by  any  of  the 
approved  methods  in  common  use. 

The  method  described  by  Blair,  designed  especially  for  the  es- 
timation of  vanadium  in  iron  and  steel,  is  conducted  in  the  follow- 
ing manner:36  Five  grams  of  the  drillings  are  dissolved  in  50 
cubic  centimeters  of  nitric  acid  of  1.24  specific  gravity.  The  solu- 
tion is  evaporated  to  dryness  in  a  porcelain  dish  and  heated  there- 
after until  the  nitrates  are  nearly  decomposed.  After  cooling, 
the  dried  mass  is  transferred  to  a  mortar  and  finely  ground 
with  30  grams  of  dry  sodium  carbonate  and  three  grams  of 
sodium  nitrate.  The  finely  ground  materials  are  placed  in  a 
platinum  dish  and  fused  for  an  hour  at  a  high  temperature. 
Spread  the  fused  mass  over  the  sides  of  the  dish  while  cooling, 
and  afterwards  dissolve  in  hot  water,  filter,  and  wash  until  the 
volume  is  a  little  over  half  a  liter.  Add  nitric  acid  to  decompose 
carbonates,  but  not  completely,  and  boil  to  get  rid  of  carbon 
dioxid,  being  careful  to  keep  the  mass  always  slightly  alkaline. 
Add  nitric  acid,  drop  by  drop,  until  slightly  in  excess,  and  then 
sodium  carbonate  to  marked  alkalinity,  boil,  and  filter.  Add  a 
slight  excess  of  nitric  acid  to  the  filtrate,  and  the  development  of 
a  yellow  color  will  indicate  the  presence  of  vanadic  acid.  Add 
to  the  solution  a  small  quantity  of  mercurous  nitrate  and  then  an 
excess  of  mercuric  oxid,  suspended  in  water  to  render  the  solu- 
tion neutral  and  insure  the  complete  precipitation  of  mercurous 
vanadate.  The  mercurous  salt  also  precipitates  phosphoric, 
chromic,  tungstic,  and  molybdic  acids  which  may  be  present. 
Boil,  filter,  and  wash  the  precipitate  with  hot  water,  dry,  and 
ignite.  Fuse  the  residue  with  sodium  carbonate  and  a  little 
nitrate.  Dissolve  the  fused  mass,  after  cooling,  in  a  little  water 
54  The  Chemical  Analysis  of  Iron,  6th  Edition,  1906  :  203. 


276  AGRICULTURAL  ANALYSIS 

and  filter.  Add  to  the  filtrate  ammonium  chlorid  in  excess 
about  3.5  grams  for  each  10  cubic  centimeters  of  the  solution, 
and  allow  to  stand,  with  occasional  stirring,  for  some  time.  Am- 
monium vanadate,  insoluble  in  a  saturated  solution  of  ammonium 
chlorid,  separates  as  a  white  powder.  It  is  necessary  to  keep  the 
solution  alkaline,  and  a  drop  of  ammonia  should  be  added  from 
time  to  time  for  this  purpose.  The  appearance  of  a  yellowish 
tint  at  any  time  indicates  that  the  solution  has  become  acid,  and 
this  acidity  must  be  corrected,  or  else  the  results  will  be  too  low. 
Separate  the  ammonium  vanadate  by  filtration ;  wash  first  with 
a  saturated  solution  of  ammonium  chlorid  containing  a  little  free 
ammonia,  and  then  with  alcohol.  Dry,  ignite,  and  moisten  with  a 
few  drops  of  nitric  acid ;  again  ignite  to  obtain  the  compound  as 
vanadium  pentoxid,  V2O5.  This  compound  contains  56.22  per 
cent,  of  vanadium. 

The  method  of  Rosenheim  and  Holverscheit  may  also  be  used.37 
It  is  based  on  the  preliminary  precipitation  of  the  vanadic  acid  as 
a  barium  or  lead  salt.  The  substance  supposed  to  contain  vana- 
dium is  first  brought  into  solution  in  such  a  manner  as  to  secure 
it  as  vanadic  acid,  which  is  then  precipitated  with  barium  chloric! 
or  lead  acetate.  The  precipitate  is  boiled  with  hydrochloric  acid 
and  potassium  bromid,  and  the  liberated  bromin  determined  by  the 
quantity  of  iodin  set  free  from  potassium  iodid.  In  the  absence  of 
bodies,  such  as  molybdic  acid,  which  are  reduced  by  sulfurous 
acid  or  hydrogen  sulfid  the  vanadic  acid  may  also  be  determined 
by  reducing  it  with  one  of  these  reagents  and,  after  removing  the 
excess  by  boiling,  titrating  the  vanadium  tetroxid  with  potas- 
sium permanganate.  When  vanadic  and  phosphoric  acids  occur 
together  the  former  may  be  first  reduced  to  tetroxid  with  sulfurous 
acid,  and  after  expelling  excess  of  this  reagent,  the  phosphoric 
acid  may  be  separated  with  molybdate  solution  and  removed  by 
filtration.  When  the  amount  of  vanadic  acid  is  large  the  phos- 
phoric acid  should  be  separated  rapidly  at  55°-6o°,  using  a  con- 
siderable excess  of  the  molybdate ;  or  the  vanadic  acid  may  first  be 
determined  in  the  solution  volumetrically  by  the  bromin  pro- 

87  Ueber  Vanadinwolfratnsame,  Dissertation,  Berlin,  1888. 

Ueber  die  quantitative  Bestimmung  des  Vanadins.     Dissertation,  Ber- 
lin, 1890. 


MANUFACTURE   OF    SUPERPHOSPHATES  277 

cess  above  described,  and  afterwards  the  phosphoric  acid 
obtained  by  evaporating  to  dryness  with4  a  little  sulfuric  acid, 
taking  the  residue  up  with  water,  reducing  the  vanadic  with  sul- 
furous  acid  and  precipitating  the  phosphoric  acid  with  molyb- 
date  solution  as  described  above. 

CHEMISTRY  OF  SUPERPHOSPHATE  MANUFACTURE 
237.  Chemical  Changes  in  the  Manufacture  of  Superphosphates. 
—In  this  country  the  expressions  "acid"  and  "super"  as  applied 
to  phosphates  are  used  interchangeably.  A  more  correct  use  of  the 
terms  would  designate  by  "acid"  the  phosphate  formed  directly 
from  tricalcium  phosphate  by  the  action  of  sulfuric  acid,  while  by 
"super"  would  be  indicated  a  similar  product  formed  by  the  action 
of  free  phosphoric  acid  on  the  same  materials.  In  Germany  the  lat- 
ter compound  is  called  "double  phosphate." 

The  reaction  which  takes  place  in  the  first  instance  is  repre- 
sented by  the  following  formula : 

3Ca3(P04)2+6H2S04+i2H20=4H3P04+Ca3(P04)2-f- 
6(CaSO4.2H2O)  ; 

and4H3P04-fCa3(P04)2-f3H20=3[CaH4(P04)2.H20]. 
A  simpler  form  of  the  reaction  is  expressed  as  follows : 
Ca3(P04)2+2H2S04+5H20 
=CaH4(PO4)2.H2O+2[CaSO4.2H2O]. 

If  310  parts,  by  weight,  of  finely  ground  tricalcium  phosphate 
be  mixed  with  196  parts  of  sulfuric  acid  and  90  parts  of  water, 
and  the  resulting  jelly  be  quickly  diluted  with  a  large  quantity 
of  water,  and  filtered,  there  will  be  found  in  the  filtrate  about 
three-quarters  of  the  total  phosphoric  as  free  acid.  If,  however,, 
the  jelly,  at  first,  formed  as  above,  be  left  to  become  dry  and  hard, 
the  filtrate,  when  the  mass  is  beaten  up  with  water  and  filtered, 
will  contain  monocalcium  phosphate,  CaH4(PO4)2. 

If  the  quantity  of  sulfuric  acid  used  be  not  sufficient  for  com- 
plete decomposition,  the  dicalcium  salt  is  formed  directly  accord- 
ing to  the  following  reaction : 

Ca3(PO4)2+H2SO4+6H2O 
= Ca2H,  ( PO4 )  2.4H2O+  CaSO4.2H2O. 
This  arises,  doubtless,  by  the  formation,  at  first,  of  the  regular 


278  AGRICULTURAL  ANALYSIS 

monocalcium  salt  and  the  further  reaction  of  this  with  the  tri- 
calcium  compound,  as  follows: 

'   CaH4(P04)2+H20+Ca8(P04)2+7H20 
=2[Ca2H2(P04)2.4H20]. 

This  reaction  represents,  theoretically,  the  so-called  reversion 
of  the  phosphoric  acid.     When  there  is  an  excess  of  sulfuric  acid 
there  is  a  complete  decomposition  of  the  calcium  salts  with  the 
production  of  free  phosphoric  acid  and  gypsum.     The  reaction 
is  represented  by  the  following  formula: 
Ca3(P04)2-f3H2S04-f6H20 
=2H8PO4+3[CaSO4.2H2O]. 

The  crystallized  gypsum  absorbs  the  six  molecules  of  water  in 
its  molecular  structure.  While  the  above  reactions  represent  the 
theoretical  conditions,  there  is  a  wide  divergence  from  them  in 
actual  manufacture.  In  the  case  of  dissolved  bone,  especially,  the 
actual  quantity  of  sulfuric  acid  used  is  not  so  great  as  is  indi- 
cated. The  proportions  of  acid  and  raw  materials  are  necessarily 
changed  from  time  to  time  to  meet  the  emergencies  which  may 
arise. 

238.  Reactions  with  Fluorids. — Since  calcium  fluorid  is  pres- 
ent in  nearly  all  mineral  phosphates,  the  reactions  of  this 
compound  must  be  taken  into  consideration  in  a  chemical  study 
of  the  manufacture  of  acid  phosphates.  When  treated  with  sul- 
furic acid  the  first  reaction  which  takes  place  consists  in  the  for- 
mation of  hydrofluoric  acid :  CaF2  -f-  H2SO4  =  2HF  -(-  CaSO4. 
Since,  however,  there  is  generally  some  silica  in  reach  of  the 
nascent  acid,  all,  or  a  portion  of  it,  combines  at  once  with  this 
silica,  forming  silicon  tetrafluorid :  4HF-|-SiO2=2H2O-|-SiF4. 
This  compound,  however,  is  decomposed  at  once  in  the  presence 
of  water,  forming  hydrofluosilicic  acid :  3SiF4-}-2H2O=SiO2+ 
2H2SiF6.  The  presence  of  calcium  fluorid  in  natural  phosphates 
is  extremely  objectionable  from  a  technical  point  of  view,  both 
on  account  of  the  increased  consumption  of  oil  of  vitriol  which 
it  causes,  and  also  by  reason  of  the  injurious  nature  of  the  gaseous 
fluorin  compounds  produced.  Each  100  pounds  of  calcium  flu- 
orid entails  the  consumption  of  125.6  pounds  of  sulfuric  acid,  for 
which  no  economic  return  is  secured. 


IRON  AND  ALUMINA  COMPOUNDS  279 

239.  Reaction  with  Carbonates. — Most  mineral  phosphates  con- 
tain   calcium    carbonate  '  in    varying    quantities.      This    com- 
pound is  decomposed  on  treatment  with  sulfuric  acid  according 
to  the  reaction:     CaCO3+H2SO4— CaSO4+H2O+ CO2.     When 
present  in  moderate  amounts,  calcium  carbonate  is  not  an  objec- 
tionable impurity  in  natural  phosphates  intended  for  acid  phos- 
phate manufacture.     The  reaction  with  sulfuric  acid  which  takes 
place  produces  a  proper  rise  in  temperature  throughout  the  mass, 
while  the  escaping  carbon  dioxid  permeates  and  lightens  the  whole 
mass,  assisting  thus  in  completing  the  chemical  reaction  by  leaving 
the  residual  mass  porous,  and  capable  of  being  easily  dried  and  pul- 
verized.    Where  large  quantities  of  carbonate  in  proportion  to 
the  phosphate  are  present  the  sulfuric  acid  used  should  be  dilute 
enough  to  furnish  the  necessary  water  of  crystallization  to  the 
gypsum  formed.     For  each  100  parts,  by  weight,  of  calcium  car- 
bonate,  80   parts   of   sulfuric    anhydrid    are    necessary,   or    125 
parts  of  acid  of  1.710  specific  gravity=6o°  Beaume. 

In  some  guanos  a  part  of  the  calcium  is  found  as  pyrophos- 
phate,  and  this  is  acted  upon  by  the  sulfuric  acid  in  the  follow- 
ing way :  Ca2P2O7+H2SO4=CaH2P,O7+CaSO4. 

240.  Solution  of  the  Iron  and  Alumina  Compounds. — Iron  may 
occur   in    natural   phosphates    in    many    forms.     It    probably    is 
most  frequently  met  with  as  ferric  or  ferrous  phosphate,  seldom  as 
ferric  oxid,  and  often  as  pyrite,  FeS2.  The  iron  also  may  sometimes 
exist  as  a  silicate.     The  alumina  is  found  chiefly  in  combination 
with  phosphoric  acid,  and  as  silicate. 

Where  a  little  less  sulfuric  acid  is  employed,  as  is  generally 
the  case,  than  is  necessary  for  complete  solution,  the  iron  phos- 
phate is  attacked  as  represented  below : 

3FeP04+3H2S04=FeP04.2H3P04+Fe2(S04)3. 

When  an  excess  of  sulfuric  acid  is  employed,  the  formula  is 
reduced  to  the  simple  one : 

2FeP04+3H2S04=2H3P04+Fe2(S04)3. 

A  part  of  the  iron  sulfate  formed  reacts  with  the  acid  calcium 
phosphate  present  to  produce  a  permanent  jelly-like  compound, 
difficult  to  dry  and  handle.  As  much  as  two  per  cent,  of  iron 


280  AGRICULTURAL  ANALYSIS 

phosphate,  however,  may  be  present  without  serious  interference 
with  the  commercial  handling  of  the  'product.  By  using  more 
sulfuric  acid,  as  much  as  four  or  five  per  cent,  of  the  iron  phos- 
phate can  be  held  in  solution.  Larger  quantities  are  very  trouble- 
some from  a  commercial  point  of  view.  The  reaction  of  the 
ferric  sulfate  with  monocalcium  phosphate  is  as  follows : 
3CaH  ( P04 )  2+Fe2  ( SO4 )  3.+4H2O=2  ( FePO4.2H3PO4.2H2O )  + 
3CaSO4. 

Pyrite  and  the  silicates  containing  iron  are  not  attacked  by 
sulfuric  acid  and  these  compounds  are  therefore  left,  in  the  final 
product,  in  a  harmless  state.  If  the  pyritic  iron  is  to  be  brought 
into  solution  aqua  regia  should  be  employed. 

With  sufficient  acid  the  aluminum   phosphate  is  decomposed 
with  the  formation  of  aluminum  sulfate  and  free  phosphoric  acid : 
A1P04+  3H2S04= A12  ( S04 )  3+2H3P04. 

241.  Reaction  with  Magnesium  Compounds. — The  mineial  phos- 
phates,   as    a    rule,    contain    but    little    magnesia.     When    pres- 
ent it  is  probably  as  an  acid  salt,  MgHPO4.     Its  decomposition 
takes  place  in  slight  deficiency  or  excess  of  sulfuric  acid,  respect- 
ively, as  follows: 

2MgHPO4+H,SO4+2H2O:=  [  MgH4  ( PO4 )  2.2H2O  ] + MgSO4 
and  MgHPO4+H2SO4=H3PO4+MgSO4. 

The  magnesia,  when  in  the  form  of  oxid,  is  capable  of  pro- 
ducing a  reversion  of  the  monocalcium  phosphate,  as  is  shown 
below : 

CaH4  ( PO4)  2-f  MgO=CaMgH2  ( PO4)  2+ H2O. 
One  part  by  weight  of  magnesia  can  render  three  and  one-half 
parts  of  soluble  monocalcium  phosphate  insoluble. 

242.  Determination  of  Quantity  of  Sulfuric  Acid  Necessary  for 
Solution  of  a  Mineral  Phosphate. — The  theoretical  quantity  of 
.sulfuric  acid  required  for  the  proper  treatment  of  any  phosphate 
may  be  calculated  from  its  chemical  analysis  and  by  the  formulas 
and  reactions  already  given.     For  the  experimental  determination 
the  method  of  Riimpler  may  be  followed.38 

Twenty  grams  of  the  fine  phosphate  are  placed  in  a  liter  flask 
38  Kaufliche  Diingestoffe  und  ihre  Anwendung,  4th  Edition,    1897  :  Si. 


SOLUTION  OF  A   MINERAL  PHOSPHATE  28l 

with  a  greater  quantity  of  accurately  measured  sulfuric  acid  than 
is  necessary  for  complete  solution.  The  acid  should  have  a 
specific  gravity  of  1.455  or  45°  B.  The  mixture  is  allowed  to 
stand  for  two  hours  at  50°.  It  is  then  cooled,  the  flask  filled 
with  water  to  the  mark,  well  shaken,  and  the  contents  filtered. 
Fifty  cubic  centimeters  of  the  filtrate  are  treated  with  tenth-nor- 
mal soda-lye,  free  of  carbonate,  until  basic  phosphate  begins  to 
separate  and  becomes  permanent  after  shaking.  The  excess  of 
acid  is  then  calculated.  Example :  Twenty  grams  of  phosphate 
containing  28.3  per  cent,  of  phosphoric  acid,  10.0  per  cent,  of 
calcium  carbonate,  5.5  per  cent,  of  calcium  fluorid,  and  2.4  per 
cent,  of  calcium  chlorid  were  treated  as  above  with  16  cubic  centi- 
meters of  sulfuric  acid  containing  10.24  grams  of  sulfur  trioxid. 
In  titrating  50  cubic  centimeters  of  the  filtrate  obtained  as  de- 
scribed above,  10.4  cubic  centimeters  of  tenth-normal  soda-lye 
were  used,  equivalent  to  0.0416  gram  of  sulfur  trioxid.  Then  10.24 
X5CH- 1000=0.5  i2O=total  sulfur  trioxid  in  50  cubic  centimeters 
of  the  filtrate,  and  0.5120 — 0.0416—0.4704  gram,  the  amount  of 
sulfur  trioxid  consumed  in  the  decomposition. 

Therefore  the  sulfur  trioxid  required  for  decomposition  is 
47.04  per  cent,  of  the  weight  of  the  phosphate  employed. 
One  hundred  parts  of  the  phosphate  would,  therefore,  require 
47.04  parts  of  sulfur  trioxid  equal  to  73.6  parts  of  sulfuric  acid  of 
1.710  specific  gravity  or  92.1  parts  of  1.530  specific  gravity. 

A  more  convenient  method  than  the  one  mentioned  above,  con  - 
sists  in  treating  a  small  quantity  of  the  phosphate,  from  one-half 
to  one  kilogram,  in  the  laboratory,  or  50  kilograms  in  a  lead 
box  just  as  would  be  practiced  on  a  large  scale.  A  few  tests 
with  these  small  quantities,  followed  by  drying  and  grinding, 
will  reveal  to  the  skilled  operator  the  approximate  quantity  and 
strength  of  sulfuric  acid  to  be  used  in  each  case.  The  quanti- 
ties of  sulfuric  acid  as  determined  by  calculation  from  analyses 
and  by  actual  laboratory  tests  agree  fairly  well  in  most  instances. 
There  is,  however,  sometimes  a  marked  disagreement.  The 
general  rule  of  practice  is  to  use  always  an  amount  of  sulfuric 
acid  sufficient  to  produce  and  maintain  water-soluble  phosphoric 
acid  in  the  fertilizer,  but  the  sulfuric  acid  must  not  be  used  in 


282  AGRICULTURAL  ANALYSIS 

such  quantity  as  to  interfere  with  the  subsequent  drying,  grind- 
ing, and  marketing  of  the  acid  phosphate. 

For  convenience,  the  following  table  may  be  used  for  calcula- 
ting the  quantity  of  oil  of  vitriol  needed  for  the  entire  decomposi- 
tion of  each  unit  of  weight  of  material  noted. 

ONE  PART  BY  WEIGHT  OF  EACH  SUBSTANCE  BELOW  REQUIRES  : 

Sulfunc  Acid  by  Same  Unit  of  Weight. 


At  48°  B.     At  50°  B.      At  52°  B.     At  54°  B.     At  55°  B. 

Tricalcium  phosphate I-59Q  1.517  1.446  1.382  1.352 

Iron  phosphate 1.630  1.558  1.485  1.420  1.390 

Aluminum  phosphate 2.025  I-93°  T"839  1.756  1.721 

Calcium   carbonate 1.640  1.565  1-495  1.428  1.411 

Calcium  fluor id 2.006  2.010  1.916  1.830  1-794 

Magnesium  carbonate 1.940  1.860  1-775  1.690  1.660 

Example. — Suppose  for  example  a  phosphate  of  the  following 
composition  is  to  be  treated  with  sulfuric  acid;  viz.,89 

Moisture  and  organic  matter 4.00  per  cent. 

Calcium  phosphate 55-oo  " 

Calcium  carbonate 3.00  " 

Iron  and  aluminum  phosphate  nearly  all  alumina  6.50  " 

Magnesium  carbonate 0.75  " 

Calcium  fluorid 2.25  " 

Insoluble 28.00  " 

Using  sulfuric  acid  of  50°  B.,  the  following  quantities  will  be 
required  for  the  weights  mentioned: 

Kilos  of  acid  required. 

Calcium  phosphate,  fifty -five  kilos 83.44 

"        carbonate,  three  and  a  half  kilos 5.48 

"        fluorid,  two  and  a  quarter      "     4.52 

Aluminum  and  iron  phosphate,  six  and  a  half  kilos 12.55 

Magnesium  carbonate,  three-quarters  of  a  kilo  1.40 

Total  68  kilos 107.39 

Since  only  a  partial  decomposition  is  attained  in  actual  manu- 
facture the  quantity  of  50°  Beaume  acid  required  is  often  less  than 
the  weight  of  phosphate  treated. 

243.  Phosphoric  Acid  Superphosphates. — If  a  mineral  phosphate 
be  decomposed  by  free  phosphoric  acid  in  place  of  sulfuric  acid, 
the  resulting  compound  will  contain  about  three  times  as  much 
39  Wyatt,  Phosphates  of  America,  4th  Edition,  1892  ;  128. 


PHOSPHORIC  ACID  IN  BASIC  SOILS  283 

available  phosphoric  acid  as  is  found  in  the  ordinary  acid  phos- 
phate. The  reaction  takes  place  according  to  the  following' 
formulas : 

(1)  Ca3(P04)2H-4H3P04+3H20^3[CaH4(P04),H20]. 

(2)  Ca3(P04)2+2H3P04+i2H20=3[Ca2H2(P04),4H20]. 
In  each  case  the  water  in  the  final  product  is  probably  united  as 

crystal  water  with  the  calcium  salts  produced.  The  monocal- 
cium  salt  formed  in  the  first  reaction  is  soluble  in  water,  and  the 
dicalcium  salt  in  the  second  reaction,  in  ammonium  citrate. 
Where  fertilizers  are  to  be  transported  to  great  distances,  there 
is  a  considerable  saving  of  freight  by  the  use  of  such  a  high- 
grade  phosphate,  which  may,  at  times,  contain  over  40  per  cent, 
of  available  acid.  The  phosphoric  acid  used  in  this  process  is 
made  directly  from  the  mineral  phosphate  by  treating  it  with  an 
excess  of  sulfuric  acid. 

244.  Fixation  of  Phosphoric  Acid  in  Basic  Soils. — The  problem 
of  holding  phosphoric  acid  in  the  soil  probably  does  not  come 
within  the  scope  of  this  manual,  except  as  incident  to  the  character 
and  time  of  its  application.  This  subject  has  been  studied  by 
Crawley.40 

Experimentally,  the  determination  of  the  holding  powers  of 
the  soil  for  the  phosphoric  acid  obtained,  depends  upon  the  same 
methods  as  are  described  for  the  absorption  of  salts  by  soils.41 
In  the  irrigated  soil  with  which  Crawley  worked,  it  was 
found  that,  when  the  application  of  fertilizer  containing  water- 
soluble  phosphoric  acid  was  followed  immediately  by  irrigation, 
more  than  one-half  of  the  soluble  phosphoric  acid  remained  in 
the  first  inch  of  the  soil  and  more  than  nine-tenths  in  the  first  three 
inches,  and  practically  the  whole  of  it  within  the  first  six  inches, 
of  the  surface.  Crawley  concludes  from  the  results  of  his  investi- 
gations that  the  water-soluble  phosphoric  acid  does  not  become 
so  widely  distributed,  in  the  case  of  heavy  rains  or  irrigation 
beneath  the  surface,  as  has  been  expected.  In  this  connection 
however,  attention  should  be  called  to  the  fact  that  the  Hawaiian 

40  Journal  of  the  American  Chemical  Society,  1902,  24  :  1114- 
11  Principles  and  Practice  of  Agricultural  Analysis,  and  Edition,   1906, 
1  :  133- 


AGRICULTURAL  ANALYSIS 

soils  on  which  Crawley  worked,  are  very  strongly  basic  and  hence 
are  in  a  condition  better  suited  to  fix  and  hold  the  phosphoric 
acid  than  the  acidic  soils  with  which  the  chemist  is  usually  called 
upon  to  work.  The  obvious  conclusion  from  an  experimental 
work  of  this  kind  is  that  in  determining  the  power  of  any  par- 
ticular soil  for  holding  the  phosphoric  acid  applied  to  it,  its 
character,  especially  as  regards  its  acidity  or  basicity,  should  be 
carefully  considered. 

245.  Absorption  of  Phosphoric  Acid  of  Superphosphates.42 — Mr. 
Joffre  states  that  contrary  to  what  is  usually  thought,  the  com- 
binations soluble  in  water  appear  to  be  absorbed  by  vege- 
tation. The  proportion  absorbed  is,  without  doubt,  very  small, 
but  it  may  have  a  very  great  importance  because  the  absorption 
takes  place  at  a  moment  when  the  plants  have  used  up  the  ma- 
terial in  the  seed  and  have  not  yet  developed  sufficiently  to  evapo- 
rate the  large  quantity  of  water  and  to  be  able  thus  to  extract  from 
the  soil  the  useful  substances,  difficultly  soluble,  which  there 
exist. 

This  theory  explains  perfectly  the  results  of  the  remarkable 
researches  of  Schloesing  and  Prunet  who  have  found  that,  when 
fertilizers  are  planted  in  the  rows,  they  produce  greater  effects 
than  when  they  are  mixed  with  the  soil.  This  evidence  depends 
upon  the  fact  that  when  they  are  planted  in  rows,  they  become 
soluble  less  rapidly  and  the  plants  thus  have  more  time  to  absorb 
the  combinations  of  phosphoric  acid  soluble  in  water. 

On  page  698  of  the  same  volume,  Joffre  continues  the  dis- 
cussion of  the  subject.  In  this  communication  he  has  subjected 
to  field  experiments,  the  operations  which  he  has  previously  con- 
ducted in  the  laboratory.  He  says:  "Moreover,  in  the  culture 
experiment  made  in  pure  sand  where  there  was  nothing  which 
could  produce  insolubility  of  phosphate  soluble  in  water  and 
where  it  is  seen  that  this  body  causes  an  increase  in  the  crops,  it  is 
necessary  to  admit  that  the  combinations  of  phosphoric  acid  solu- 
ble in  water  enter  into  the  plant  and  are  assimilated  there.  I 
have  not  said  that  insoluble  phosphate  is  without  utility  in  agricul- 
ture. It  produces,  indeed,  in  certain  earth  effects  which  are  as 
«  Bulletin  de  la  Soci£t£  chitnique  de  Paris,  1895,  [3],  13  :  522. 


PHYSICAL  CONDITION  OF  AVAILABILITY  285 

beneficial  as  the  soluble  phosphate,  but  in  the  greater  part  of  soils, 
if  it  produces  an  action,  this  action  is  less  than  that  of  superphos- 
phates and  the  inferiority  of  this  action  appears  to  be  caused,  at 
least  in  part,  because  no  portion  of  it  can  enter  immediately  into 
the  plant  in  a  condition  of  aqueous  solution. 

"To  resume,  the  whole  of  my  experiment  seems  to  make  clear 
that  the  favorable  action  of  superphosphate  is  not  only  caused  by  a 
greater  dissemination  of  the  combinations  of  phosphoric  acid  in 
the  arable  earth,  but  that  it  is  also  necessary  to  take  into  account 
the  absorption  in  the  form  of  combinations,  soluble  in  water,  of  a 
portion  of  soluble  phosphoric  acid  of  superphosphates.  If  we 
desire  to  obtain  a  maximum  result  it  is  necessary  to  distinguish  two 
sorts  of  soil ;  first,  the  soil  analogous  to  those,  of  which  numerous 
examples  are  found  in  Bretagne,  in  which  insoluble  phosphates 
succeed  as  well  as  superphosphates  and  where  it  is  natural  to  em- 
ploy phosphate  simply  ground.  Second,  the  other  soils  which  are 
far  more  numerous  and  in  which  the  phosphoric  acid  fertilizers  in 
combinations  soluble  in  water  are  absolutely  indispensable  to  ob- 
tain the  maximum  effect." 

246.  Physical  Condition  of  Availability. — In  general  it  may 
be  said  that  the  physical  state  of  subdivision  of  raw  phosphates 
and  basic  slags  is  one  of  the  most  important  factors  in  respect 
of  their  availability.  This  degree  of  fineness,  however,  depends 
for  its  efficiency  largely  on  other  conditions,  especially  where  arti- 
ficial means  are  employed  for  determining  availability.  For 
this  reason  it  is  advisable,  when  determining  the  availability  of 
these  materials  by  chemical  means,  to  employ  extremely  dilute 
solutions.  The  method  of  Dyer  depends  on  the  use  of  an  organic 
acid  and  of  Moore  upon  the  use  of  a  mineral  acid ;  both  require 
•great  degrees  of  attenuation.43  Only  by  the  use  of  some  such  re- 
agent can  the  conditions  which  occur  in  nature  be  simulated, 
yet  it  must  not  be  considered  that  the  same  degree  of  attenuation 
must  be  present  in  the  artificial  means  as  in  the  natural.  Otherwise 
the  time  of  experimental  determinations  of  the  artificial  means 
would  have  to  continue  over  several  months  instead  of  several 
hours.  It  is  possible  that  a  revision  of  the  common  idea  respect- 

**  Principles  and  Practice  of  Agricultural  Analysis,   and  Edition,  1906, 
1  :  394,  459- 


286  AGRICULTURAL  ANALYSIS 

ing  the  action  which  takes  place  in  the  soil  will  show  that  the 
plant  itself  exudes  no  solvent  material  as  has  been  assumed  by 
many  investigators,  unless  it  be  the  excretion  of  carbon  dioxid. 
The  processes  of  solution  which  take  place  in  the  soil,  from  a 
study  of  all  the  conditions  which  obtain,  must  be  regarded  more 
as  operations  depending  upon  the  soil  itself  than  as  largely  in- 
fluenced by  the  growing  plant.  At  the  present  time,  however, 
the  solution  of  the  problem,  experimentally,  in  so  far  as  fineness 
of  subdivision  is  concerned,  has  perhaps  been  well  answered  and 
it  is  now  clearly  understood  that  in  so  far  as  the  assimilation 
processes  go  on  in  the  soil,  they  are  favored  more  particularly  by 
the  fineness  of  the  subdivisions  than  by  any  other  factor.  Even 
in  soils  which  are  not  distinctly  acid  the  fineness  of  subdivision 
greatly  favors  solution,  and  in  regard  to  the  other  causes  of  solu- 
tion and  absorption  of  these  bodies,  excluding  those  due  to 
weathering,  it  is  probable  that  our  ideas  in  the  near  future  must 
undergo  fundamental  revision.  Just  at  present  we  are  unable  to- 
specify  whether  or  not  the  frequent  application  of  these  par- 
tially insoluble  phosphatic  fertilizers  is  advisable  or  not.  Some 
authors  urge  that  when  the  crop  is  to  be  planted  in  the  spring  these 
fertilizers  should  be  applied  in  the  autumn,  while  some  are  of  the 
opinion  that  equally  good  results  are  obtained  by  applying  them 
at  the  time  of  sowing.44 

Reitmair  concludes  from  his  investigations  that  the  extraction- 
of  bones  in  such  a  way  as  to  remove  practically  all  of  their  nitro- 
gen does  not  unfit  them  for  fertilizing  purposes,  since  the  resid- 
ual phosphate  of  lime  when  reduced  to  a  proper  state  of  fineness 
is  still  valuable  for  its  phosphoric  acid. 


**  Reitmair,  Wiener  landwirtschaftliche  Zeitung,  1905,  55  :  879,  889. 


PART  SECOND 


NITROGEN  IN  FERTILIZERS,  DRAINAGE  WATERS,  ETC. 

247.  Kinds  of  Nitrogen  in  Fertilizers. — Nitrogen  is  the  most 
costly  of  the  essential  plant  foods.  It  has  been  shown  in  the  first 
volume  that  the  popular  notion  regarding  the  relatively  great 
abundance  of  nitrogen  is  erroneous.  It  forms  only  a  minute  part 
of  the  matter  in  and  pertaining  to  the  earth's  crust.  The  great 
mass  of  nitrogen  forming  the  bulk  of  the  atmosphere  is  inert 
and  useless  in  respect  of  its  adaptation  to  plant  food.  It  is  not 
until  it  becomes  oxidized  by  combustion,  electrical  discharges, 
or  the  action  of  certain  micro-organisms  that  it  assumes  an  agri- 
cultural value. 

2.48.  States  of  Nitrogen. — Having  described  the  relation  of  nitro- 
gen to  the  soil  in  the  first  volume,  it  remains  the  sole  province 
of  the  present  part  to  study  it  as  aggregated  in  a  form  suited  to 
plant  food.  In  this  function  nitrogen  may  claim  the  attention  of 
the  analyst  in  the  following  forms: 

1.  In  organic  combination  in  animal  or  vegetable  substances, 
forming  a  large  class  of  bodies,  of  which  protein  may  be  taken 
as  the  type.     Dried  blood  or  cottonseed-meal  illustrates  this  form 
of  combination. 

2.  In  the  form  of  ammonia  or  combinations  thereof,  especially 
as  ammonium  sulfate,  or  as  amid  nitrogen. 

3.  In  a  more  highly  oxidized  form  as  nitrous  or  nitric  acid, 
usually  united   with   a   base   of  which   Chile   saltpeter   may  be 
taken  as  a  type. 

The  analyst  has  often  to  deal  with  single  forms  of  nitrogenous 
-compounds,  but  in  many  instances  may  also  find  all  the  typical 
forms  in  a  single  sample.  Among  the  possible  cases  which  may 
arise,  the  following  are  types : 

a.  The  sample  under  examination  may  contain  nitrogen  in  all 
three  forms  mentioned  above. 


288  AGRICULTURAL  ANALYSIS 

b.  There  may  be  present  nitrogen  in  the  organic  form  mixed 
with  nitric  nitrogen. 

c.  Ammoniacal  nitrogen  may  replace  the  nitric  in  the  above 
combination. 

d.  The  sample  may  contain  no  organic  but  only  nitric  and 
ammoniacal  nitrogen. 

e.  Only  nitric  or  ammoniacal  nitrogen  may  be  present. 

249.  Seeds  and  Seed  Residues. — The  proteid  matters  in  seeds 
and  seed  residues,  after  the  extraction  of  the  oil,  are  highly  prized 
as  sources  of  nitrogenous  fertilizers,  either  for  direct  application, 
or  for  mixing.  Typical  of  this  class  of  substances  is  cotton- 
seed-meal, the  residue  left  after  the  extraction  of  the  oil,  which 
is  accomplished  at  the  present  time  mostly  by  hydraulic  pressure 
but  also  by  the  use  of  a  solvent.  The  residual  cakes  in  the  former 
case  still  contain  some  oil,  but  nearly  half  their  weight  consists 
of  nitrogenous  compounds.  The  following  table  gives  the  com- 
position of  a  dry  sample  of  hydraulic  pressed  cottonseed-meal : 

Ash 7.60  per  cent. 

Fiber 4.90      " 

Oil 10.01       " 

Protein 51.12       " 

Digestible  carbohydrates,  etc. .  -  •  •     26.37       " 

While  the  above  shows  the  composition  of  a  single  sample  of 
the  meal,  it  should  be  remembered  that  there  may  be  wide  varia- 
tions from  this  standard  due  either  to  natural  composition  or  to 
different  degrees  of  the  extraction  of  the  oil. 

The  composition  of  the  ash  is  given  below : 

Phosphoric  acid,  P2O5 31.01  per  cent. 

Potash,                  K20 35.50  " 

Soda,                      Na20 0.57  " 

Lime,                     CaO 5.68  " 

Magnesia,              MgO 15.19  " 

Sulfuric  acid,       SOS 3.90  " 

Insoluble 0.69  " 

Carbon  dioxid  and  undetermined.  7.46  " 

The  cakes  left  after  the  expression  of  the  oil  from  flaxseed 
and  other  oily  seeds,  are  also  very  rich  in  nitrogenous  matters ;  but 
these  residues  are  chiefly  used  for  cattle-feeding  and  only  the 
undigested  portions  of  them  pass  into  the  manure.  Cottonseed 


NITROGEN    IN    SEA-WEEDS  289 

cake-meal  is  not  so  well  suited  for  cattle-feeding  as  the  others 
mentioned,  because  of  the  cholin  and  beta'in  which  it  contains; 
often  in  sufficient  quantities  to  render  its  use  dangerous  to  young 
animals.  The  danger  in  feeding  increases  in  proportion  to  the 
total  quantity  of  the  two  bases  and  also  the  relative  quantity 
of  cholin  to  beta'in,  the  former  base  being  more  poisonous  than 
the  latter.  In  a  sample  of  the  mixed  bases  prepared  by  Maxwell 
from  cottonseed  cake-meal,  the  cholin  amounted  to  17.5  and  the 
betain  to  82.5  per  cent,  of  the  whole.45 

The  nitrogen  contained  in  these  bases  is  also  included  in  the 
total  nitrogen  found  in  the  meal.  The  actual  proteid  value  of 
the  numbers  obtained  for  nitrogen  is,  therefore,  less  than  that 
obtained  for  the  whole  of  the  nitrogen  by  the  quantity  present  as 
nitrogenous  bases. 

In  the  United  States,  cottonseed  cake-meal  is  used  in  large 
quantities  as  a  direct  fertilizer,  but  not  so  extensively  for  mixing 
as  some  of  the  other  sources  of  nitrogen.  Its  delicate  yellow 
color  serves  to  distinguish  it  at  once  from  the  other  bodies  used 
for  similar  purposes.  No  special  mention  need  be  made  of  other 
oil-cake  residues.  They  are  quite  similar  in  their  composition 
and  uses,  as  well  as  in  their  manner  of  treatment  and  analysis  to 
the  cottonseed  product. 

250.  Nitrogen  in  Sea-Weeds.— The  waste  available  nitrogen  finds 
its  way  sooner  or  later  to  the  sea,  and  is  recovered  therefrom  in 
many  forms.  Sea-weeds  of  all  kinds  are  rich  in  organic  nitrogen. 
Many  years  ago  Forchhammer  pointed  out  the  agricultural  value 
of  certain  fucoids.46  Many  other  chemists  have  contributed  im- 
portant data  in  regard  to  the  composition  of  these  bodies. 

Jenkins  has  shown  from  the  analyses  of  several  varieties  of 
sea-weeds  that  in  the  green  state  they  are  quite  equal  in  fertiliz- 
ing value  to  stall  manure,  and  are  sold  at  the  rate  of  five  cents 
per  bushel.47  These  data  are  fully  corroborated  by  Goessmann.48 

Wheeler  and  Hartwell  give  the  fullest  and  most  systematic 

45  Maxwell,  American  Chemical  Journal,  1891,  13  :  469. 

46  Journal  fur  praktische  Chemie,  1845,  [J]>  36  :  385. 

47  Annual  Report  of  the  Connecticut  Experiment  Station,  1890  :  72. 

48  Annual  Report  of  the  Massachusetts  Experiment  Station,  1887  :  223. 
10 


2QO  AGRICULTURAL  ANALYSIS 

discussion  which  has  been  published  of  the  agricultural  value  of 
sea-weeds.49  Sea-weed  was  used  as  a  fertilizer  as  early  as  the 
fourth  century,  and  its  importance  for  this  purpose  has  been 
recognized  more  and  more  in  modern  days,  especially  since  chemi- 
cal investigations  have  shown  the  great  value  of  the  food  mate- 
rials therein. 

To  show  the  commercial  importance  of  sea-weed,  it  is  only 
necessary  to  call  attention  to  the  fact  that  in  1885  its  value  as  a 
fertilizer  in  the  State  of  Rhode  Island  was  $65,044,  while  the 
value  of  all  other  commercial  fertilizers  was  only  $164,133.  While 
sea-weed,  in  a  sense,  can  only  be  successfully  applied  to  marine 
littoral  agriculture,  yet  the  extent  of  agricultural  lands  bordering 
on  the  sea  is  so  great  as  to  render  its  commercial  importance  of 
the  highest  degree  of  interest. 

251.  Dried  Blood  and  Tankage. — The  blood  and  debris  from 
abattoirs  afford  abundant  sources  of  nitrogen  in  a  form  easily 
oxidized  by  the  micro-organisms  of  the  soil.     Blood  is  prepared 
for  use  by  simple  drying  and  grinding.     The  intestines,  scraps, 
and  fragments  of  flesh  resulting  from  trimming  and  cutting  are 
placed  in  tanks  and  steamed  under  pressure  to  remove  the  fat. 
The  residue  is  dried  and  ground,  forming  the  tankage  of  com- 
merce.    The  whole  carcasses  of  animals  condemned  as  unfit  for 
food  are  reduced  to  tankage.     Dried  blood  is  richer  in  proteid 
matter  than  any  other  substance  in  common  use  for  fertilizing 
purposes.    When  in  a  perfectly  dry  state  it  may  contain  as  much 
as  14  per  cent,  of  nitrogen,  equivalent  to  nearly  88  per  cent,  of 
proteid  or  albuminoid  matter.     Tankage  is  less  rich  in  nitrogen 
than  dried  blood,  but  still  contains  enough  to  make  it  a  highly 
desirable  constituent  of  manures. 

252.  Horn,  Hoof  and  Hair. — These  bodies,  although  quite  rich 
in  nitrogen,  are  not  well  suited  to  fertilizing  purposes  on  account 
of  the  extreme  slowness  of  their  decomposition.    Their  presence, 
therefore,  should  be  regarded  in  the  nature  of  a  fraud,  because 
by  the  usual  methods  of  analysis  they  show  a  high  percentage  of 
nitrogen,  and  therefore  acquire  a  fictitious  value.     If  these  bodies 
be  treated  with  sulfuric  acid  and  rendered  soluble  their  value  as 

49  Rhode  Island  Experiment  Station,  Bulletin  21,  1893. 


Pig.  13.    Wild  Ducks  and  Eggs  on  Layson  Island. 


NITROGEN    FROM    BIRDS  29! 

a  manure  is  greatly  increased.  The  relative  value  of  the  nitro- 
gen in  these  bodies  as  compared  with  the  more  desirable  forms, 
has  been  a  much  disputed  question. 

253.  Ammoniacal  Nitrogen. — In    ammonia    compounds,    nitro- 
gen is  used  chiefly  for  fertilizing  purposes  as  sulfate.     Large 
quantities  of  ammonia  are  produced  in  the  manufacture  of  coke 
and   in  other  industrial  operations.     The  ideal  nitrogenous  fer- 
tilizer is  a  combination  of  the  ammoniacal  and  nitric  nitrogen 
found  in  ammonium  nitrate.     The  high  cost  of  this  substance 
excludes  its  use  except  for  experimental  purposes. 

254.  Nitrogen  in  Fish. — A  large  amount  of  nitrogen  is  also 
recovered  from  the  sea  in  fishes.     It  is  shown  by  Atwater  that 
the  edible  part  of  fishes  has  an  unusually  high  percentage  of 
protein.50     In  round  numbers  about  75  per  cent,  of  the  water-free 
edible  parts  of  fish  are  composed  of  albuminoids.     Some  kinds  of 
fish,  however,  are  taken  chiefly  for  their  oil  and  fertilizing  value, 
as  the  menhaden,  but  the  residue  after  the  oil  has  been  extracted 
is  even  richer  in  nitrogen  than  mentioned  above.     Squanto,  an 
American  Indian,  first  taught  the  early  New  England  settlers 
the  manurial  value  of  fish.51 

255.  Nitrogen  from  Birds. — Immense  quantities  of  waste  nitro- 
gen are  further  secured,  both  from  sea  and  land,  by  the  various 
genera  of  birds.     The  well  known  habit  of  birds  in  congregating 
in  rookeries  during  the  night  and  at  certain  seasons  of  the  year 
tends  to  bring  into  a  common  receptacle  the  nitrogenous  matters 
which  they  have  gathered  and  which  are  deposited  in  their  ex- 
crement and  in  the  decay  of  their  bodies.     In  former  times  the 
magnitude  of  these  rookeries  was  probably  much  greater  than  now, 
but  even  at  the  present  time  they  are  of  vast  extent  as  shown  by 
Fig.  13,  a  photograph  of  wild  ducks  on  Layson  Island.  The  feath- 
ers of  birds  are  particularly  rich  in  nitrogen,  and  the  nitrogenous 
content  of  the  flesh  of  fowls  is  also  high.  The  decay  of  remains  of 
birds,  especially  if  it  takes  place  largely  excluded  from  the  leach- 
ing of  water,  tends  to  accumulate  vast  deposits  of  nitrogenous  mat- 
ter. If  the  conditions  in  such  deposits  be  favorable  to  the  processes 

50  Report  of  the  Commissioner  of  Fish  and  Fisheries,   1888  :  679. 

51  Goode,  American  Naturalist,  1880,  14  :  473. 


292  AGRICULTURAL  ANALYSIS 

of  nitrification,  the  whole  of  the  nitrogen,  or  at  least  the  larger 
part  of  it,  which  has  been  collected  in  this  debris,  becomes 
finally  converted  into  nitric  acid  and  is  found  combined  with 
appropriate  bases  as  deposits  of  nitrates.  The  nitrates  of  the 
guano  deposits  and  of  the  deposits  in  caves  arise  in  this  way. 
If  these  deposits  be  subject  to  moderate  leaching  the  nitrate 
may  become  infiltered  into  the  surrounding  soil,  making  it  very 
rich  in  this  form  of  nitrogen.  The  bottoms  and  surrounding  soils 
of  caves  are  often  found  highly  impregnated  with  nitrates. 

256.  Waste  Nitrogen. — When  nitrogen  has  played  its  role  in 
vegetable  and  animal  life  it  is  broken'  down  from  the  organic 
compounds  it  has  formed  by  the  action  of  organisms,  or  in  the 
usual  processes  of  decay,  and  is  oxidized  again  to  soluble  forms, 
and  may  be  even  restored  to  its  gaseous  inorganic  condition. 

257.  Soils  Impregnated  with  Nitrogen. — While   for  our  pur- 
pose, deposits  of  nitrates  only  are  to  be  considered  which  are  of 
sufficient  value  to  bear  transportation,  or  to  warrant  their  con- 
centration by  leaching,  yet  much  interest  attaches  to  the  formation 
ot  nitrates  in  the  soil  even  when  they  are  not  of  commercial  im- 
portance. 

In  many  of  the  soils  of  tropical  regions  not  subject  to  heavy 
rain-falls,  the  accumulation  of  these  nitrates  is  very  great. 
Muntz  and  Marcano  have  investigated  many  of  these  soils  to 
which  attention  was  called  first  by  Humboldt  and  Boussingault.52 
They  state  that  these  soils  are  incomparably  more  rich  in  nitrates 
than  the  most  fertile  soils  of  Europe.  The  samples  which  they 
examined  were  collected  from  different  parts  of  Venezuela  and 
from  valleys  of  the  Orinoco,  as  well  as  on  the  shore  of  the  Car- 
ibbean Sea.  The  nitrated  soils  are  very  abundant  in  this  region 
of  South  America  where  they  cover  large  surfaces.  Their  compo- 
sition is  variable,  but  in  all  of  them  carbonate  and  phosphate  of 
lime  are  met  with  and  organic  nitrogenous  material.  The  nitric 
acid  is  found  always  combined  with  lime.  In  some  of  the  soils 
as  high  as  30  per  cent,  of  nitrate  of  lime  have  been  found.  Nitri- 
fication of  organic  material  takes  place  very  rapidly  the  year 
round  in  this  tropical  region.  These  nitrated  soils  are  everywhere 
"  Comptes  rendus,  1885,  101  :  65. 


DEPOSITS  OF  NITRATES  293 

abundant  around  caves  which  serve  as  the  refuge  of  birds  and  bats, 
as  described  by  Humboldt.  The  nitrogenous  matters,  which  come 
from  the  decay  of  the  remains  of  these  animals,  form  true  de- 
posits of  guano  which  is  gradually  spread  around,  and  which,  in 
contact  with  the  limestone  and  with  access  of  air,  suffers  com- 
plete nitrification  with  the  fixation  of  the  nitric  acid  by  the  lime. 
Large  quantities  of  this  guano  are  also  due  to  the  debris  of 
insects,  fragments  of  elytra,  scales  of  the  wings  of  butterflies, 
etc.,  which  are  brought  together  in  those  places  by  the  millions 
of  cubic  meters.  The  nitrification,  which  takes  place  in  these 
deposits,  has  been  found  to  extend  its  products  to  a  distance  of 
several  kilometers  through  the  soil.  In  some  places  the  quan- 
tity of  the  nitrate  of  lime  is  so  great  in  the  soils  that  they  are 
converted  into  a  plastic  paste  by  this  deliquescent  salt. 

258.  Deposits  of  Nitrates. — The  theory  of  Muntz  and  Marcano 
in  regard  to  the  nitrates  of  soils,  especially  in  the  neighborhood 
of  caves,  is  probably  a  correct  one,  but  there  are  many  objections 
to  accepting  it  to  explain  the  great  deposits  of  nitrate  of  soda 
which  occur  in  many  parts  of  Chile  and  other  parts  of  the  world. 
Another  point  which  must  be  considered  also,  is  this :  That  the 
process  of  nitrification  can  not  now  be  considered  as  going  on  with 
the  same  vigor  as  formerly.  Some  moisture  is  necessary  to  nitri- 
fication, inasmuch  as  the  nitrifying  ferment  does  not  act  in  perfect- 
ly dry  soil,  and  in  many  localities  in  Chile,  where  the  nitrates  are 
found,  it  is  too  dry  to  suppose  that  any  active  nitrification  could 
now  take  place. 

The  existence  of  these  nitrate  deposits  has  long  been  known.53 
The  old  Indian  laws  originally  prohibited  the  collection  of  the 
salt,  but,  nevertheless,  it  was  secretly  collected  and  sold.  Up  to 
the  year  1821,  soda  saltpeter  was  not  known  in  Europe  except 
as  a  laboratory  product.  About  this  time  the  naturalist,  Mari- 
ano de  Rivero,  found  on  the  Pacific  coast,  in  the  Province  of 
Tarapaca,  immense  new  deposits  of  the  salt.  Later  the  salt  was 
found  in  equal  abundance  in  the  Territory  of  Antofogasta,  and, 
further  to  the  south,  in  the  desert  of  Atacama,  which  forms  the 
Department  of  Taltal. 

M  Journal  of  the  Royal  Agricultural  Society,  1852,  13  :  349. 


294  AGRICULTURAL,  ANALYSIS 

At  the  present  time  the  collection  and  export  of  saltpeter 
from  Chile  is  a  business  of  great  importance.  The  largest  ex- 
port prior  to  1895,  in  any  one  year,  was  in  1890,  when 
the  amount  exported  was  927,290,430  kilograms;  of  this  quan- 
tity 642,506,985  kilograms  were  sent  to  Europe  and  86,124,870 
kilograms  to  the  United  States.  Since  that  time  the  imports  of 
this  salt  into  the  United  States  have  slowly  increased. 

The  exportations  from  Chile  during  the  years  1903,  1904  and 
1905  were  1,445,000,  1,480,000  and  1,627,000  tons  of  2204 
pounds,  respectively.  During  these  three  years  there  were  im- 
ported directly  into  the  United  States  90,000,  75,000  and  117,000 
tons,  respectively.54  The  consumption  of  nitrate  of  soda  in  the 
United  States  is  greater  than  the  direct  importation  indicates, 
since  considerable  quantities  come  into  the  country  from  Europe. 
The  total  consumption  in  Europe  in  1903  was  1,296,694  tons, 
and  in  the  United  States  259,993  tons.  The  total  quantity  of  the 
salt  exported  from  Chile  from  1840  to  1903,  inclusive,  is  25,947,- 
944  tons.  The  total  quantity  produced  in  Chile  in  1905  was 
1,733,644  tons,  three-quarters  of  which  were  used  as  fertilizers. 
The  quantity  coming  to  the  United  States  during  that  year  was 
353,177  tons.  The  total  nitrate  production  of  Chile  in  1907  was 
2,100,000  short  tons  of  which  373,988  tons,  valued  at  $13,118,214 
were  directly  or  indirectly  imported  into  the  United  States.  The 
ratio  of  increase  in  exportation  is  rapidly  decreasing,  having  fallen 
from  124  per  cent,  for  the  five  years  1870-74  to  11.5  per  cent. 
for  the  four  years  I9OO-O3.55  In  1905  there  were  78  factories 
in  Chile  engaged  in  the  nitrate  industry.  In  order  to  maintain 
prices  a  trust  of  the  operators  has  been  formed,  regulating  the 
amount  which  each  factory  may  produce.  About  55  tons  of 
salt  are  produced  annually  for  each  laborer  employed.  The  price 
per  ton  to  wholesale  American  consumers  ranges  from  $45  to  $53. 
It  is  estimated  that  at  the  present  rate  of  consumption,  the  sup- 
ply from  Chile  will  rapidly  diminish  in  about  20  years.56 

According  to  Pissis  these  deposits  are  of  very  ancient  origin. 
84  L'Engrais,  1906,  21  :  35. 

55  American  Fertilizer,  1905,  22  :  5. 

56  American  Fertilizer,  1905,  22  :  6. 


THE    NITER  DEPOSITS   OF    CALIFORNIA  295 

This  geologist  is  of  the  opinion  that  the  nitrate  deposits  are  the 
result  of  the  decomposition  of  feldspathic  rocks;  the  bases  thus 
produced  gradually  becoming  united  with  the  nitric  acid  pro- 
vided from  the  air.57 

According  to  the  theory  of  Nollner,  the  deposits  are  of  more 
modern  origin  and  due  to  the  decomposition  of  marine  vegeta- 
tion.58 Continuous  solution  of  soils  gives  rise  to  the  formation 
of  great  lakes  of  saturated  water,  in  which  occur  the  develop- 
ment of  much  marine  vegetation.  On  the  evaporation  of  this 
water,  due  to  geologic  isolation,  the  decomposition  of  nitrogen- 
ous organic  matter  causes  generation  of  nitric  acid,  which,  coming 
in  contact  with  the  calcareous  rocks,  attacks  them,  forming  nitrate 
of  calcium,  which,  in  presence  of  sulfate  of  sodium,  gives  rise  to 
a  double  decomposition  into  nitrate  of  sodium  and  sulfate  of 
calcium. 

The  fact  that  iodin  is  found  in  greater  or  less  quantity  in 
Chile  saltpeter,  is  one  of  the  chief  supports  of  this  hypothesis  of 
marine  origin,  inasmuch  as  iodin  is  always  found  in  sea  and  not 
in  terrestrial  plants.  Further  than  this,  it  must  be  taken  into 
consideration  that  these  deposits  of  nitrate  of  soda  contain  neither 
shells  nor  fossils,  nor  do  they  contain  any  phosphate  of  lime. 
The  theory,  therefore,  that  they  are  due  to  animal  origin,  is 
scarcely  tenable. 

Extensive  nitrate  deposits  have  been  discovered  in  the  U.  S. 
of  Columbia.59  These  deposits  have  been  found  extending 
over  30  square  miles  and  vary  in  thickness  from  one  to  10  feet. 
The  deposits  consist  of  a  mixture  of  sodium  nitrate,  sodium 
chlorid,  calcium  sulfate,  aluminum  sulfate  and  insoluble  silica, 
and  contain  from  one  to  13.5  per  cent,  of  nitrate. 

259.  The  Niter  Deposits  of  California. — Many  of  the  condi- 
tions which  favor  the  deposition  of  niter  in  the  soil  are  found  in 
Southern  California  and  Arizona,  and  it  has  been  confidently 
predicted  that  niter  deposits  of  value  and  of  great  extent  would 
bo  found  in  these  localities.  The  California  State  Mining  Bureau 

57  Fuchs  and  de  Launay,  Traitd  des  Giles  mine'raux,  1893,  1  :  425. 

58  Le  Feuvre  and  Dagnino,  El  Salitre  de  Chile,  1893  :  12. 

59  Wiley,    Presidential    Address,   Journal   of  the    American    Chemical 
Society,  1894,  16  :  20. 


296  AGRICULTURAL  ANALYSIS 

has  made  investigations  of  the  deposits  of  niter  in  Southern  Cali- 
fornia, and  has  collected  practically  all  of  the  exact  information 
that  is  available  on  the  subject.60  Nearly  all  of  the  niter  deposits 
which  have  been  discovered  up  to  the  present  time  are  found  in 
the  northern  part  of  San  Bernardino  County,  and  the  beds  are 
found  particularly  along  the  shore  lines,  or  old  beaches  that 
mark  the  boundary  of  Death  Valley  as  it  doubtless  appeared 
ouring  the  eocene  times.  The  beds  and  clays  contain  the  de- 
posits which  have  been  worn  by  erosive  agencies  into  knobs, 
buttes  and  ridges  that  have  been  compared  by  some  to  haystacks 
and  potato  hills. 

Until  lately  the  principal  value  of  the  niter  hills  was  sup- 
posed to  lie  solely  in  the  surface  coating.  When  this  is  removed, 
deposits  which  are  full  of  other  saline  compounds  are  exposed. 
This  top  coating  is,  in  accordance  with  the  custom  followed  in 
Chile,  called  by  the  Spanish  name  "caliche."  This  caliche  ranges 
in  depth  from  a  few  inches  to  several  feet.  The  surface  caliche 
evidently  owes  its  deposits  of  salt  to  the  upward  capillary  flow 
of  water  from  below,  induced  by  the  rapid  evaporation  at  the 
surface  in  a  region  comparatively  devoid  of  rains.  The  niter 
deposit  is  in  the  form  of  a  soluble  salt,  which  readily  permeates 
the  clay  and  separates  into  a  white  crystalline  deposit.  In  Chile 
the  colors  of  the  caliche  are  usually  yellow,  pink  and  green,  but 
in  California  a  creamy  yellow  is  the  characteristic  color;  though 
pinks  and  greens  are  sometimes  found.  The  quantity  of  niter 
contained  in  the  caliche  is  extremely  minute  as  compared  with 
the  more  concentrated  deposits  of  Chile,  and  hence  it  is  evident 
that  these  extensive  deposits  in  California  will  not  become  avail- 
able commercially,  until  the  more  concentrated  deposits  in  Chile 
and  other  similar  localities  are  exhausted.  The  chief  difficulty  in 
the  California  deposits  is  that  the  niter  is  associated  with  other 
soluble  salts,  chiefly  common  salt,  from  which  it  is  with  some 
difficulty  separated.  The  following  table  gives  typical  examples 
of  the  composition  of  the  soluble  salts  of  the  caliche,  not  the 
representative  or  mean  composition,  but  the  extreme  types  of 
samples  containing  various  proportions  of  niter : 

60  California  State  Mining  Bureau,  Bulletin  24,  1902  :  154. 


FUNCTIONS  OF  SODIUM    NITRATE  297 


Niter  (NaNO.)  

i 

7  28 

2 

3 

4 

5 

7.20 
6  16 

7  <;6 

60 

•3U 

.  J.U 

Sulfate  of  Magnesium  .  . 

•     1.30 

.   84  26 

2.80 

7/1    1A 

2.00 
.dfi  76 

•3° 
1.  2O 

21  40 

1.20 

It  was  found  that  the  average  composition  of  104  samples 
of  caliche,  taken  from  as  many  different  claims,  was  9.54  per  cent, 
of  niter.  The  quantity  of  niter  which  has  been  located  in  South- 
ern California  is  difficult  to  estimate.  The  following  estimate 
comprises  the  whole  amount  of  niter  which  is  thought  to  exist 
in  the  small  areas  surveyed,  but  it  does  not  indicate  what  can 
be  commercially  extracted.  About  35,000  acres  of  the  deposit 
have  been  examined,  in  which  it  is  estimated  that  there  exist 
about  22,000,000  tons  of  nitrate  of  soda.  This,  of  course,  is  only 
a  very  rough  estimate  and  is  perhaps  of  little  value  in  basing 
computations  of  the  future  supply. 

In  general,  it  may  be  said  that  the  niter  beds  of  California  are 
at  the  present  time  of  little  importance  from  a  commercial  point 
of  view.  Not  only  is  the  amount  of  niter  comparatively  small, 
but  the  distance  from  markets  and  the  cost  of  transportation 
are  so  great  as  to  practically  exclude  the  product  from  the  mar- 
kets of  the  world. 

It  is  stated  by  Pennock  that  no  commercial  success  has  at- 
tended the  exploitation  of  nitrate  deposits  in  the  United  States.61 
According  to  the  same  author  the  production  of  nitrate  of  soda 
is  practically  confined  to  Chile. 

260.  Functions  of  Sodium  Nitrate. — Practically  the  only  form 
of  oxidized  nitrogen  which  is  of  importance  from  an  agronomic 
point  of  view  is  sodium  nitrate,  often  known  in  commerce  by 
the  name  Chile  saltpeter.  Ammoniacal  compounds  and  nitrites 
are  usually  oxidized  to  nitric  acid  or  its  compounds  before  they 
are  assimilated  as  plant  foods.  Applied  to  a  growing  crop,  sodium 
nitrate  at  once  becomes  dissolved  at  the  first  rainfall  or  by  the 
natural  moisture  of  the  soil.  It  carries  thus  to  the  rootlets  of 
•'  Journal  of  the  American  Chemical  Society,  1906,  28  :  1248. 


298  AGRICULTURAL  ANALYSIS 

plants  a  supply  of  nitrogen  in  the  most  highly  available  state. 
There  is  perhaps  no  other  kind  of  plant  food  which  is  offered  to 
the  living  vegetable  in  a  more  completely  predigested  state,  and 
none  to  which  a  quicker  response  will  be  given.  By  reason  of 
its  high  availability,  however,  it  must  be  used  with  care.  A  too 
free  use  of  such  a  stimulating  food  may  have,  in  the  end,  an 
injurious  effect  upon  the  crop,  and  is  quite  certain  to  lead  to  the 
waste  of  a  considerable  portion  of  expensive  material.  For  this 
reason  sodium  nitrate  should  be  applied  with  extreme  care,  in 
small  quantities  at  a  time,  and  only  when  it  is  needed  by  the 
growing  crop.  It  would  be  useless,  for  instance,  to  apply  this 
fertilizer  in  the  autumn  with  the  expectation  of  its  benefiting 
the  crop  to  a  maximum  degree  the  following  spring.  Again,  if 
the  application  of  this  salt  should  be  made  just  previous  to  a 
heavy  rain,  almost  or  quite  the  whole  of  it  would  be  removed 
beyond  the  reach  of  the  absorbing  organs  of  the  plant. 

When  once  the  nitric  acid  has  been  absorbed  by  the  living 
rootlet  it  is  held  with  great  tenacity.  Living  plants  macerated 
in  water  give  up  only  a  trace  of  nitric  acid,  but  if  they  be  pre- 
viously killed  with  chloroform,  the  nitric  acid  they  contain  is 
easily  leached  out. 

The  molecule  of  sodium  nitrate  is  decomposed  by  dissociation 
or  otherwise  in  the  process  of  the  absorption  of  the  nitric  acid. 
The  acid  enters  the  plant  organism  and  the  soda  is  left  to  combine 
with  the  soil  acids.  The  nascent  soda  may  thus  play  a  role  of 
some  importance  in  decomposing  particles  of  minerals  contain- 
ing potash  or  phosphoric  acid.  Some  authorities  say  the  decom- 
position of  the  sodium  nitrate  takes  place  in  the  cells  of  the  ab- 
sorbing plant  organs,  for  it  is  difficult  to  understand  how  it 
could  be  accomplished  externally.  While  the  soda,  therefore,  is 
of  no  importance  as  a  direct  plant  food,  it  can  hardly  be  dis- 
missed as  of  no  value  whatever  in  the  process  of  fertilization. 
Many  of  the  salts  of  soda,  as,  for  instance,  common  salt,  are  quite 
hygroscopic  and  serve  to  attract  moisture  from  the  air  and  thus 
become  carriers  of  water  between  the  plant  and  the  air  in  sea- 
sons of  drought;  and  sodium  nitrate  itself  is  so  hygroscopic  as 
not  to  be  suited  to  the  manufacture  of  gunpowder. 


ADULTERATION   OF  CHILE  SALTPETER  299 

To  recapitulate:  The  chief  functions  of  sodium  nitrate  are  to 
give  to  the  plant  a  supply  of  oxidized  nitrogen  ready  for  absorp- 
tion into  its  tissues  and  incidentally  to  aid,  by  the  residual  soda, 
in  the  decomposition  of  silt  particles  containing  potash  or  phos- 
phoric acid  and  in  supplying  to  the  soil  salts  of  a  more  or  less 
deliquescent  nature. 

261.  Commercial  Forms   of  Chile    Saltpeter. — The   Chile   salt- 
peter of  commerce  may  reach  the  farmer  or  analyst  in  the  lumpy 
state  in  which  it  is  shipped,  or  as  finely  ground  and  ready  for 
application  to  the  fields.     Unless  the   farmer  is  provided  with 
means  for  grinding,  the  latter  condition  is  much  to  be  preferred. 
It  permits  of  a  more  even  distribution  of  the  salt,  and  thus  en- 
courages economy  in  its  use.     For  the  chemist  also  it  is  advan- 
tageous to  have  the  finely  ground  material,  which  condition  per- 
mits more  easily  a  perfect  sampling,  a  process  which,  with  the 
unground  salt,  is  attended  with  no  little  difficulty. 

262.  Percentage   of  Nitrogen  in  Chile  Saltpeter. — Chemically 
pure  sodium  nitrate  contains  16.49  Per  cent,  of  nitrogen.     The 
salt  of  commerce  is  never  pure.     It  contains  moisture,  potash, 
magnesia,  lime,  sulfur,  chlorin,  iodin,  silica  and  insoluble  mate- 
rials, and  traces  of  other  bodies.    The  value  of  the  salt  depends, 
therefore,  not  only  on  the  market  value  of  nitrogen  at  the  time 
of  sale,  but  also  on  its  content  of  nitrogen.    The  nitrate  of  com- 
merce varies  greatly  in  its  nitrogen  content  and  is  sold  on  a 
guaranty  of  its  purity.     The  best  grades  range  in  nitrogen  from 
15  to  1 6  per  cent.     The  content  of  nitrogen  has  long  been  esti- 
mated in  the  trade  by  determining  the  other  constituents  and 
counting  the  rest  as  nitrogen.     This  practice  arose  in   former 
times  when  no  convenient  method  was  at  hand  for  determining 
nitric  nitrogen.     The  process  is  tiresome  and  unreliable,  because 
all  errors  of  every  kind  are  accumulated  in  the  nitrogen  content, 
1)ut  inasmuch  as  the  method  is  still  required  by  many  merchants, 
the  analyst  should  be  acquainted  with  it,  and  it  is  therefore  given 
further  along.     The  usual  methods  for  determining  nitric  nitro- 
gen may  be  applied  in  all  cases  where  samples  of  sodium  nitrate 
are  under  examination,  but  some  special  processes  are  described 
further  on  for  convenience. 

263.  Adulteration  of  Chile  Saltpeter. — The  analyst,  aside  from 


300  AGRICULTURAL,  ANALYSIS 

the  honesty  of  the  dealer,  is  the  only  protector  of  the  farmer  in 
guarding  against  the  practice  of  adulteration  of  sodium  nitrate. 
Even  the  honest  dealer  is  compelled  to  protect  himself  against 
fraud,  and  therefore,  the  world  over,  commerce  in  this  fertilizer 
is  now  conducted  solely  on  the  analyst's  certificate.  Happily, 
therefore,  adulteration  is  almost  unknown,  because  it  is  certain 
to  be  detected.  Formerly,  the  saltpeter  was  adulterated  with 
common  salt,  or  low  grade  salts  from  the  potash  mines;  but  it 
is  an  extremely  rare  thing  now  to  find  any  impurities  in  the  salts 
other  than  those  naturally  present. 

In  every  case  the  analyst  may  grow  suspicious  when  he  finds 
the  content  of  nitrogen  in  a  sample  to  fall  below  13  per  cent.  It 
must  not  be  forgotten,  however,  that  some  potassium  nitrate  may 
be  present  in  the  sample,  and  since  that  salt  contains  only  13.87 
per  cent,  of  nitrogen,  its  presence  would  tend  to  lower  the  value 
of  the  fertilizer;  but  although  the  potash  itself  is  a  fertilizer  of 
value,  it  is  not  worth  more  than  one-third  as  much  as  nitrogen. 
In  all  cases  of  suspected  adulteration,  it  is  advisable  to  make 
a  complete  analysis.  The  results  of  this  work  will,  as  a  rule, 
lead  the  analyst  to  a  correct  judgment. 

264.  The  Application  of  Chile  Saltpeter  to  the  Soil. — The 
analyst  is  often  asked  to  determine  the  desirability  of  the  use  of 
sodium  nitrate  as  a  fertilizer  and  the  methods  and  times  of  ap- 
plying it.  These  are  questions  which  are  scarcely  germane  to 
the  purpose  of  this  work,  but  which,  nevertheless,  for  the  sake 
of  convenience,  may  be  briefly  discussed.  In  the  first  place,  it 
may  be  said  that  the  data  of  a  chance  chemical  analysis  will  not 
afford  a  sufficiently  broad  basis  for  an  answer.  A  given  soil 
may  be  very  rich  in  nitrogen  as  revealed  by  chemical  analysis, 
and  yet  poor  in  art  available  supply.  This  is  frequently  the  case 
with  vegetable  soils,  containing,  as  they  do,  large  quantities  of 
nitrogen,  but  holding  it  in  practically  an  inert  state.  I  have 
found  such  soils  very  rich  in  nitrogen,  yet  almost  entirely  devoid 
of  nitrifying  organisms.  It  is  necessary,  therefore,  in  reaching  a 
judgment  on  this  subject  from  analytical  data  to  consider  the 
different  states  in  which  the  nitrogen  may  exist  in  a  soil,  and 
above  all,  the  nitrifying  power  of  the  soil  if  the  nitrogen  be 


UTILIZATION   OF   NITROGEN  30 1 

chiefly  present  in  an  organic  state.  Culture  solutions  should 
therefore  be  seeded  with  samples  of  the  soil  under  examination 
and  the  beginning  and  rapidity  of  the  nitrification  carefully  noted. 
In  conjunction  with  this  the  nitrogen  present  in  the  soil  in  a  nitric 
or  ammoniacal  form  should  be  accurately  determined. 

The  quantities  of  Chile  saltpeter  which  should  be  applied  per 
acre  vary  with  so  many  conditions  as  to  make  any  definite  state- 
ment impossible.  On  account  of  the  great  solubility  of  this  salt, 
no  more  should  be  used  than  is  necessary  for  the  nutrition  of  the 
crop.  For  each  100  pounds  used,  from  14  to  15  pounds  of  nitro- 
gen will  be  added  to  the  soil.  Field  crops,  as  a  rule,  will  require 
less  of  the  salt  than  garden  crops.  There  is  an  economic  limit 
to  the  application  which  should  not  be  passed.  As  a  rule,  250 
pounds  per  acre  is  a  maximum  dressing  for  field  crops.  The 
character  of  the  crop  must  also  be  considered.  Different  amounts 
are  required  for  sugar  beets,  tobacco,  wheat,  and  other  standard 
crops.  It  is  rarely  the  case  that  a  crop  demands  a  dressing  of 
Chile  saltpeter  alone.  It  will  give  the  best  effects,  as  a  rule,  when 
applied  with  phosphoric  acid  or  potash.  But  this  is  a  branch  of 
the  subject  which  cannot  be  entered  into  at  greater  length  in 
this  manual.  The  reader  is  referred  to  Weitz's  work  on  Chile 
saltpeter  for  further  information.62 

265.  The  Utilization  of  Nitrogen  in  fhe  Air  as  a  Fertilizing 
Material. — The  only  form  of  plant  which  has  developed  these  tu- 
bercles to  any  extent  is  the  legumes.  It  is,  therefore,  commonly 
understood  that  the  nitrifying  organisms  of  symbiotic  forms  are 
confined  to  leguminous  plants.  At  the  same  time,  mention  is  made 
in  Volume  I  of  the  possible  direct  nitrifying  of  atmospheric  nitro- 
gen without  the  intervention  either  of  any  organic  form  thereof, 
or  the  activity  of  other  symbiotic  nitrifying  activity.  Some  of 
the  results  of  earlier  workers  in  this  field  seem  to  indicate  the 
existence  of  organisms  which  are  capable  of  directly  nitrifying 
atmospheric  nitrogen  and  making  it  available  as  a  fertilizing 
material.  These  earlier  ideas  which  are  mentioned  in  Volume  I, 
have  of  late  years  received  further  investigation,  with  the  result 
of  establishing  more  firmly  the  belief  that  nitrification,  indepen- 

62  Der  Chilisalpeter  als  Diingemittel,  1905. 


302  AGRICULTURAL  ANALYSIS 

dent  of  the  processes  commonly  associated  therewith,  may  some- 
times take  place.03 

The  influence  of  oxid  of  iron  in  the  soil  in  rendering  available 
the  nitrogen  of  the  air,  has  received  special  attention.  Bonnema 
has  given  to  this  subject  careful  consideration  and  has  come  to 
the  conclusion  that  the  so-called  fixation  of  atmospheric  nitrogen 
in  the  soil  is  dependent  upon  the  presence  of  ferric  hydroxid. 
This  substance  appears  to  have  the  property  of  oxidizing  ele- 
mental nitrogen  and  changing  it  into  nitrous  acid,  which  is  capa- 
ble of  conversion  into  nitric  acid  in  the  usual  manner. 

It  appears  from  this  investigation  that  the  first  step  in  the 
nourishment  of  a  plant  by  atmospheric  nitrogen  is  not  necessarily 
one  of  biological  chemistry,  but  rather  one  of  a  simple  elementary 
process.64 

This  problem  has  lately  been  studied  more  closely  by  Sestini.65 
It  appears  from  the  investigation  made  by  Sestini  that  it  is  not 
the  elemental  nitrogen  of  the  air,  but  the  ammonia  which  is  con- 
tained therein  which  is  oxidized  by  ferric  hydroxid  into  nitric  acid. 
This  is  an  important  observation  in  view  of  the  fact  that  it  is 
generally  supposed  that  the  ammonia  which  enters  the  soil  from 
the  air  is  converted  into  nitrous  acid  through  the  activity  of  nitri- 
fying ferments.  The  utilization  of  the  oxid  of  iron,  therefore,  is 
not  directed  to  the  increase  of  the  total  quantity  of  assimilable 
nitrogen,  but  only  to  the  change  of  the  ammonia  into  an  assimi- 
lable form.  This  has  an  important  bearing  upon  the  study  of 
the  chemical  processes  relating  to  fertilizing  materials  by  reason 
of  the  relation  of  ammonia  to  fertility.  The  highly  beneficial  ef- 
fects produced  by  the  application  of  ammonia  salts  have  long 
been  recognized.  Most  observers  claim  that  these  salts  are  only 
useful  when  converted  into  nitric  acid,  and  others  that  they  are 
useful  in  the  absence  of  ferments  which  can  produce  this  change. 
In  either  case,  however,  it  is  evident,  in  view  of  the  observations 
above  mentioned,  that  ammonia  is  not  directly  assimilable  ever. 

61  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  2nd  Edition, 
1906,  1  :  568. 

64  Chemilcer-Zeitung,  1903,  27  :  149. 

65  Die  landwirtschaftlichen  Versuchs-Stationen,  1904,  60  :  103. 


UTILIZATION   OF  ATMOSPHERIC   NITROGEN  303 

in  the  cases  last  mentioned,  but  only  after  being  converted  into  a 
more  highly  oxidized  form  by  the  activity  of  ferric  hydroxid. 

It  seems  to  be  established  that  ferric  hydroxid  at  ordinary 
temperature,  that  is,  from  15°  to  25°,  develops  a  catalytic 
influence  on  ammonia  and  ammonia  salts,  and  that  under  this 
influence  an  assimilable  form  of  nitrogen  is  developed  in  the  soil 
independently  of  the  activity  of  nitrifying  ferments,  even  in  the 
presence  of  large  quantities  of  thymol  or  of  corrosive  sublimate 
up  to  two  per  cent.,  quantities  which  are  entirely  sufficient  to 
inhibit  the  action  of  the  ordinary  nitrifying  ferments.  The  am- 
monia of  the  air  and  of  the  soil  may  thus  be  converted  into  nitrous 
acid  by  the  oxidation  produced  under  the  influence  of  the  catalytic 
activity  of  ferric  hydroxid. 

266.  The  Utilization  of  Atmospheric  Nitrogen  by  Other  Plants 
Than  Legumes. — The  evidence  which  seeks  to  establish  the  fact 
that  other  plants  than  legumes  are  capable  of  utilizing  atmos- 
pheric nitrogen  is  not  wholly  conclusive.  Theoretically,  it  seems 
a  rather  strange  provision  of  nature  that  only  plants  of  the  legu- 
minous family  should  have  the  faculty,  either  symbiotically  with 
nitrifying  organisms  or  directly,  to  utilize  atmospheric  nitrogen 
as  a  source  of  plant  food.  Nevertheless,  the  greater  number  of 
carefully  conducted  experiments  in  which  all  sources  of  possible 
error  are  excluded,  have  led,  as  a  rule,  to  negative  results  with 
other  plants,  so  that  it  can  scarcely  be  affirmed  with  any  scientific 
certainty  that  this  property  of  plants  is  a  general  or  even  a  com- 
mon one.  On  the  other  hand,  in  a  review  of  this  subject  in  con- 
nection with  research  work,  Jamieson  has  reached  the  conclusion 
that  the  property  of  utilizing  atmospheric  nitrogen  belongs  to 
many  other  forms  of  plants  besides  the  legumes.66  In  this  re- 
port Jamieson  undertakes  to  establish  the  fact  that  the  legume 
tubercle  theory  is  untenable,  and  that  the  nitrogen  of  the  air  is 
directly  utilized  by  plants  in  general.  In  all  the  plants  examined 
by  him,  structures  which  absorb  free  nitrogen  from  the  air  and 
transform  it  into  the  organic  state  were  found.  Seventeen  forms 
of  plants  of  widely  different  character  are  said  by  Jamieson  to 
have  been  examined  and  found  to  possess  the  property  indicated. 

66  Report    of     the   Agricultural    Research     Association   of  the   North- 
eastern Counties  of  Scotland,  1905  :  16. 


3O4  AGRICULTURAL   ANALYSIS 

The  plants  which  are  least  capable  of  utilizing  atmospheric  nitro- 
gen are  the  monocotyledons,  and  especially  the  cereals  and  grasses. 
According  to  Jamieson,  the  chlorophyll  cell  seems  to  possess 
in  a  high  degree  the  property  of  transforming  nitrogen,  and  the 
function  of  the  green  cell,  in  this  particular,  is  analogous  to  that 
possessed  by  it  of  utilizing  the  carbon  of  the  carbon  dioxid 
in  the  air  for  the  purpose  of  producing  organic  compounds.  He 
claims  to  have  established  the  fact,  that  the  free  nitrogen  in  the 
air  is  directly  absorbed  and  transformed  into  organic  compounds 
by  these  cells. 

The  number  of  these  organs,  their  nature,  and  their  apti- 
tude to  exercise  their  functions  vary  considerably  from  one  plant 
to  another.  In  particular,  the  monocotyledons  such  as  the  cereals 
and  grasses  are  very  poorly  endowed  with  the  organs  from  the 
point  of  view  of  the  fixation  of  nitrogen.  The  form  of  these 
organs  also  varies  greatly  and  the  different  forms  observed  by 
Jamieson  are  described  in  his  work.  These  organs  are  called 
producers  of  protein,  and  are  not  met  with  in  general  except  in 
the  tender  part  of  the  very  young  leaves  or  their  petioles.  At 
the  beginning  of  their  formation  they  do  not  contain  any  pro- 
tein. When  these  organs  are  completely  developed  the  produc- 
tion of  protein  begins  and  the  organs  are  sometimes  gorged  with 
protein,  and  this  continues  for  a  certain  length  of  time.  The 
plants  which  are  most  apt  to  fix  a  great  deal  of  nitrogen  do  not 
have  need  of  nitrogen  fertilizers,  provided  they  find  at  the  begin- 
ning of  their  development  favorable  conditions  that  will  permit 
the  proper  growth  of  the  organs  which  produce  the  protein.  In- 
stead of  buying  nitrogenous  fertilizers  as  a  greater  aid  to  the 
plants  which  are  able  to  fix  only  little  nitrogen,  such  as  cereals 
and  grasses,  it  will  be  sufficient  to  cultivate  those  plants  which 
absorb  and  fix  a  great  deal  of  nitrogen  and  thus  to  incorporate 
this  nitrogen  in  the  soil. 

These  observations  are  cited  solely  to  call  attention  to  them.  If 
confirmed  by  future  investigations,  they  wili  prove  useful  in  prac- 
tical agriculture  in  securing  a  more  abundant  supply  of  nitrogen- 
ous material  for  plant  growth. 

267.  Accumulation  and  Utilization  of  Atmospheric  Nitrogen 
in  the  Soil. — Interesting  investigations  have  been  made  on  this 


ATMOSPHERIC    NITROGEN    IN    THE    SOIL  305 

point  by  Voorhees  and  L,ipman.6T  The  experiments  conducted  were 
so  arranged  as  to  bring  out  the  relation  of  leguminous  crops, 
such  as  cow  peas,  to  soil  and  nitrogen  and  to  determine,  as  far 
as  practicable,  the  value  of  this  leguminous  crop  as  a  source  of 
nitrogen  to  subsequent  non-leguminous  crops.  The  soils  selected 
contained  an  abundance  of  phosphoric  acid  and  potash.  The 
facts  established  by  the  investigation  are  of  practical  importance, 
in  respect  of  the  possibility  of  accumulating  nitrogen  in  the  soil 
directly  from  atmospheric  nitrogen.  The  greater  number  of  the 
investigations  were  of  negative  value,  but  a  sufficient  positive  gain 
was  found  in  some  cases  to  indicate  that  further  investigation  may 
develop  methods  to  promote  the  fixation  of  nitrogen  in  the  soil. 
The  authors  admit  that  the  probability  of  the  continued  fixation 
of  nitrogen,  in  the  manner  in  which  the  investigations  were  made, 
is  not  very  great.  Attention  is  called  to  the  fact,  however,  that 
the  present  knowledge  of  bacteriological  conditions  in  the  soil  is 
still  so  limited,  that  a  general  and  successful  inoculation  with 
non-symbiotic  nitrogen-fixing  bacteria  is  out  of  the  question. 
There  is  also  a  danger  to  be  avoided  in  the  attempt  to  increase 
the  soil  nitrogen  by  means  of  the  inoculation  of  leguminous  plants, 
where  large  quantities  of  leguminous  material  are  incorporated 
in  the  soil,  as  shown  by  researches  above  mentioned.  The  nitro- 
gen-decomposing bacteria  can  develop  freely  and  the  denitrifying 
organisms  may  set  free  more  nitrogen  than  the  nitrifying  organ- 
isms fix. 

Therefore,  the  practical  problem  of  the  utilization  of  atmos- 
pheric nitrogen  as  a  fertilizing  material  is  to  be  considered,  and 
the  conditions  which  determine  the  comparative  rate  of  nitrifi- 
cation and  denitrification  are  to  be  carefully  studied  in  order  that 
valuable  results  may  be  reached. 

The  authors  also  found  that  even  under  carefully  controlled 
conditions  there  was  no  uniform  gain  of  nitrogen  due  to  the 
inoculation  of  soils  with  nitrifying  ferments.08 

The  investigation  shows  that  there  was  no  decided  gain  in 
nitrogen  in  the  inoculated  soil  after  the  inoculation.  There  was, 

67  Journal  of  the  American  Chemical  Society,  1905,  27  :  556. 

68  New  Jersey  State  Agricultural  Experiment  Station,   25th  Annual  Re- 
port, 1904  :  239. 


306  AGRICULTURAL,   ANALYSIS 

in  all  cases,  a  loss  01  nitrogen  during  the  summer  when  the  soils 
were  kept  bare,  and  the  losses  were  greatest  where  manure  had 
been  used. 

These  data  show  that  the  problem  of  increasing  soil  nitrogen 
in  a  uniform  manner  through  the  oxidation  of  atmospheric  nitro- 
gen is  still  unsolved.  There  is  probably  no  other  one  problem 
of  greater  importance  to  agriculture.  The  nitrogenous  fertilizers 
are  of  dominant  importance,  both  by  reason  of  their  high  cost  and 
of  the  necessity  of  their  presence  in  order  that  the  other  fertil- 
izing materials  in  the  soil  shall  be  duly  utilized.  There  are  many 
indications,  however,  that  in  the  near  future  the  method  for  the 
utilization  of  atmospheric  nitrogen  by  direct  oxidation  thereof 
in  the  field,  either  with  or  without  the  aid  of  growing  plants, 
may  be  discovered  and  thus  the  farmer  made  more  independent 
of  the  nitrogen  now  stored  in  various  parts  of  the  earth  or  pro- 
duced by  manufacturing  operations. 

268.  Manufacture  and  Use  of  Cyanamid  for  Fertilizing  Pur- 
poses.— Cyanamid  has  the  general  formula  H2N :  CN.  With 
univalent  metals  it  yields  metallic  compounds  corresponding  to 
M2N :  CN.  In  investigating  the  manufacture  of  cyanids  by 
means  of  carbids,  Frank  and  Caro  observed  that  if  moist  atmos- 
pheric nitrogen  be  passed  through  a  retort  heated  to  dull  redness 
and  containing  a  mixture  of  calcium  and  barium  carbids,  the 
nitrogen  becomes  fixed  to  the  metal  with  formation  of  cyanid ; 
besides  cyanid,  other  nitrogenous  compounds,  e.  g.,  cyanamid, 
due  in  part  to  the  action  of  the  cyanid  already  formed  and  in 
part  to  the  direct  action  of  the  reacting  mass,  as  the  following 
equations  indicate,  are  formed:69 

X(2MCN)+XN=X(M2NCN)  +  (CN)X 
M2C2-fN2=M2NCN-fC 

The  formation  of  cyanamid  may  be  increased  by  giving  the 
carbid  a  large  surface  thus  allowing  a  large  amount  of  nitrogen  to 
act  upon  a  small  quantity  of  carbid.  Frank  and  Caro's  process 
is  based  on  this  observation. 

The  process  of  the  Deutsche  Gold  und  Silber  Scheide  Anstalt 

69  Robine  and  Lenglen,  The  Cyanid  Industry,  Translated  by  LeClerc, 
1906,  :  144. 


CYANAMID    COMPOUND    AS    A    FERTILIZER  307 

for  the  preparation  of  cyanamid  uses  carbon  in  the  solid  state  or 
in  the  form  of  hydrocarbon  gas,  and  an  alkali  amid;  or  NH3 
brought  in  contact  with  a  melted  alkali  metal  and  charcoal  at 
4OO°-6oo0.  In  this  way,  alkali  amid  is  formed  which  under  the 
action  of  a  portion  of  the  charcoal  becomes  alkali  cyanamid.70 

Calcium  cyanamid  (the  formula  of  which  when  pure  is  CaCN2) 
is  a  black  powder,  resembling  basic  slag  in  other  properties  and 
containing  over  20  per  cent.  N,  readily  soluble  in  H2O,  besides 
more  or  less  CaO,  CaC2  and  C. 

Gerlach  found  it  to  be  equal  in  manurial  value  to  XaXO.. 
and  (NH4)2SO4  in  pot  experiments  with  barley  and  white  mus- 
tard, though  in  field  experiments  its  value  fell  to  74  (NaNO3= 
ioo).71  With  peaty  soils,  calcium  cyanamid  acts  injuriously,  due 
probably  to  the  formation  of  dicyanodiamid  by  the  organic  acids, 
unless  the  application  of  the  manure  be  made  five  or  six  weeks 
before  sowing. 

This  early  application  causes  a  loss  of  nitrogen,  which  should 
be  taken  into  account  in  reckoning  its  value. 

Otto  found  it  nearly  as  efficacious  as  sodium  nitrate  when 
used  with  spinach  or  cabbage,  and  better  than  nitrate  or  ammoni- 
acal  nitrogen  in  fertilizing  maize.72 

Hall  in  comparing  it  with  ammonium  sulfate  for  fertilizing 
mangels,  swedes  and  mustard,  obtained  favorable  results.73 

The  best  way  to  determine  the  nitrogen  in  calcium  cyanamid  is 
to  digest  it  with  strong  sulfuric  acid  by  the  usual  kjeldahl  process. 

CaCN2  decomposes  in  the  soil  into  CaCO3  and  NH3 ;  this 
makes  the  soil  alkaline ;  therefore  it  is  better  to  use  acid  phos- 
phate than  disodium  phosphate.74 

269.  Cyanamid  Compound  as  a  Fertilizer. — Experiments  have 
been  conducted  by  Shutt  and  Charlton  at  the  agricultural  ex- 
periment station  at  Ottawa  to  determine  the  value  of  cyan- 
amid compound  as  a  fertilizer.  The  effect  of  the  compound 

70  Robine  and  Lenglen,  The  Cyanid  Industry,  Translated  by  LeClerc , 
1906 :  176. 

71  Biedermann's  Central-Blatt,  1904,  33  :  649. 
77  Chemisches  Central-Blatt,  1905,  I  :  117. 

73  Journal  of  Agricultural  Science,  1905,  1  :  146. 

74  Inamura,  Bulletin  of  the  College  of  Agriculture,  Tokyo,  1906,  7  :  53- 


308  AGRICULTURAL  ANALYSIS 

upon  the  vitality  of  seeds  was  first  studied.  The  result  of  these 
experiments  was  to  show  that  the  cyanamid  compound,  except 
in  very  minute  quantities,  injuriously  affected  the  vitality  of  the 
seed.  As  the  amount  is  increased  the  toxic  effect  becomes  more 
and  more  noticeable,  not  only  in  the  retardation  of  germination, 
but  also  upon  the  health  and  vigor  of  the  ypung  plant.  Wheat  is 
better  able  to  resist  this  action  than  peas.  Nevertheless  the  wheat 
plants  in  the  tests  which  contained  the  larger  amount  of  cyanamid 
frequently  turned  black,  withered  and  died  after  reaching  a 
height  of  from  three  to  five  inches.  It  is  believed  that  cyanamid 
compound  in  amounts  not  greater  than  five  milligrams  of  nitro- 
gen to  100  grams  of  soil,  does  not  prove  injurious  to  the  germinar 
tion  of  seed.  Toxic  effects  were  markedly  noticeable,  on  the 
other  hand,  with  amounts  of  cyanamid  containing  between  10 
and  12  milligrams  of  nitrogen  per  100  grams  of  soil.  The  potas- 
sium compound  appears  to  be  more  injurious  in  action  upon  the 
life  of  the  seed  and  young  plants  than  the  calcium  salt.  In  regard 
to  the  value  of  cyanamid  compound  as  a  fertilizing  material,  the 
experiments  were  confined  to  the  study  of  its  degree  of  nitrifica- 
tion. It  would  seem  from  a  consideration  of  the  data  secured  that 
as  the  comparative  amount  of  the  cyanamid  compound  is  increased 
in  the  soil  there  is  a  corresponding  decrease  in  the  rate  of  nitrifi- 
cation. This  is  probably  due,  as  already  indicated,  to  the  toxic  ac- 
tion upon  the  nitrifying  organisms.  It  may  be  due  partly  also  to 
denitrifying  changes  leading  to  a  reduction  of  a  part  of  the 
nitrogen  to  the  free  state.  The  conversion  of  the  nitrogen  of  the 
cyanamid  into  available  forms  is  probably  continuous  under 
favorable  conditions,  though  not  uniformly  so.  The  first  stage  of 
the  process  may  be  considered  possibly  as  purely  chemical,  since 
water  at  ordinary  temperatures  converts  the  nitrogen  of  cyan- 
amid into  ammonia.  Further  changes  are  brought  about 
through  the  agency  of  living  organisms,  and  are  necessarily  slow- 
er, depending  for  their  activity  on  many  factors,  prominent  among 
which  is  the  relative  proportion  of  the  cyanamid  compound 
present  in  the  soil.75 

270.  Later  Experiments  with  Cyanamid.— Grandeau  has  sum- 
75  Chemical  News,  1906,  94  :  150. 


LATER  EXPERIMENTS  WITH  CYANAMID  309 

marized  the  latest  results  of  the  experimental  value  of  nitrate 
and  cyanamid  of  calcium  produced  by  the  electric  process  des- 
cribed later.76  The  compound  used  by  him  was  produced  by  a 
factory  in  Norway,  the  term  "Norwegian  Nitrate"  being  used  to 
distinguish  it  from  the  nitrate  of  Chile.  The  calcium  cyanamid 
when  subjected  to  the  moisture  of  the  soil  produces  ammonia. 

The  commercial  product  contains  from  20  per  cent,  to  22  per 
cent,  of  nitrogen,  while  the  sulfate  of  ammonia  contains  about  25 
per  cent.  Pure  calcium  cyanamid  CN2Ca,  contains  35  per  cent, 
of  nitrogen.  The  commercial  cyanamid  is  a  black  powder,  ground 
extremely  fine,  which  owes  its  color  to  the  carbon  which  it  con- 
tains, in  all  about  17  per  cent. 

Practical  experiments  made  by  Cart,  and  reported  to  Grandeau, 
show  that  while  the  nitrate  of  lime  acted  very  successfully  as  a 
fertilizer,  the  cyanamid  of  calcium  was  somewhat  disappointing. 
There  was  difficulty  in  spreading  this  brown  and  black  powder 
regularly,  and  in  applying  it  to  the  soil  the  fine  powder  was  ex- 
tremely irritating  to  the  face  and  hands.  The  effect  upon  the 
wheat  after  24  hours  was  described  as  being  similar  to  that  pro- 
duced by  a  solution  of  sulfate  of  copper,  while  the  wheat  treated 
with  the  nitrate  took  on  a  beautiful  green  tint  and  grew  rapidly, 
and  that  which  had  received  the  cyanamid  turned  to  a  reddish 
tint,  which  was  retained  for  at  least  a  week. 

The  total  amount  of  wheat  harvested  from  the  plot  receiving 
the  cyanamid  was  less  than  that  receiving  no  nitrogenous  fertili- 
zer at  all. 

Muntz  and  Nottin  conclude  that  the  calcium  cyanamid  does 
not  interfere  with  germination  when  employed  in  ordinary  quan- 
tities, not  exceeding  200  kilograms  per  hectare,  and  gives  good 
results. 

It  is  possible  that  the  deleterious  effects  of  the  calcium  cyan- 
amid may  be  due  to  the  fact  which  has  been  noticed  by  investi- 
gators that  in  the  manufacture  of  cyanamid  it  may  be  associated 
with  another  compound,  viz.,  dicyanamid,  the  poisonous  proper- 
ties of  which  for  plants  are  well  known.  Perhaps  the  poisonous 
action  noticed  above  by  Cart  may  have  been  due  to  such  an  ad- 
mixture. The  matter  needs  further  investigation. 
76  Journal  d' Agriculture  pratique,  1908,  72  :  229. 


310  AGRICULTURAL  ANALYSIS 

271.  Utilization  of  Atmospheric  Nitrogen. — In    the    first    vol- 
ume of  this  work  attention  has  been  called  to  the  fixation  and 
utilization   of  atmospheric   nitrogen  by  the  action   of  bacteria, 
-especially  those  living  in  symbiosis  with  leguminous  plants.77  Ber- 
thelot in  the  first  volume  of  his  Vegetable  and  Agricultural  Chem- 
istry, has  set  out  at  great  length  the  various  methods  in  which 
atmospheric  nitrogen  may  be  rendered  available  for  agricultural 
purposes.78     It  will  prove  convenient  for  the  analyst  and  student 
to  have  a  summary  of  the  different  methods  described  in  which 
atmospheric  nitrogen  may  be  rendered  useful  for  plant  food. 

The  methods  as  set  forth  by  Berthelot  are  as  follows: 

(1)  Fixation  of  atmospheric  nitrogen  by  means  of  microbes 
in  the  earth  and  upon  vegetables. 

(2)  The  continued  fixation  of  free  nitrogen  by  the  organic 
compounds  under  the  influence  of  atmospheric  electricity  of  feeble 
tension. 

(3)  The  fixation  of  nitrogen  under  the  influence  of  slow  oxi- 
dation. 

There  are  many  subdivisions  made  under  these  various  heads 
but  those  represent  in  general  the  principal  methods  which  Ber- 
thelot has  studied.  All  these  methods,  it  is  noticed,  are  purely 
natural,  that  is,  those  which  are  going  on  constantly  in  nature, 
Berthelot  not  having  taken  up  the  study  of  the  artificial  production 
of  nitrogen  under  strong  electric  influences  in  the  first  volume 
of  his  work. 

272.  Historical  Development  of  the  Fixation   of  Atmospheric 
Nitrogen  by  Means  of  Electricity. — The  principal  steps  in  the  de- 
velopment of  the  investigation  looking  to  the  fixation  of  atmos- 
pheric  nitrogen  have  been   traced   by   Erlwein.79     Attention  is 
called  to  the  researches  of  Crookes,  Lord   Rayleigh,   Bradley, 
Lovejoy,    Birkeland,    Kowalsky,    and    Pauling    in    the   research 
work  and  practical  application  of  the  principles  discovered.  Spe- 
cial    attention     is     given     to     the     work     done     by     Siemens 
and    Halske.      These    investigators    studied    the    problem    of 
the  production  of  nitric  acid  by  electrical  discharges  between 

77  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  and  Edition, 
1906.  1  :  521. 

78  Chimie  ve'ge'tale  et  agricole,  1899,  1. 

79  Elektrotechnische  Zeitschrift,    1907,    14  :  41,  62.      Electrochemical 
and  Metallurgical  Industry,  1907,  5  :  77. 


ATMOSPHERIC   NITROGEN  BY   MEANS  OF   ELECTRICITY        31 1 

heavy  carbon  electrodes.  They  also  utilized  the  horn  lightning 
arrester  consisting  of  two  vertical  horns,  the  lower  ends  of  which 
are  near  together,  while  upwards  the  two  horns  diverge  from 
each  other  more  and  more.  The  arc  is  formed  between  the  two 
lower  ends  of  these  electrodes  and  travels  upwards,  thereby  en- 
larging its  surface  and  causing  it  finally  to  be  automatically  bro- 
ken. None  of  these  methods,  however,  resulted  in  securing  oxi- 
dized nitrogen  on  a  commercial  scale.  The  development  of  the 
cyanamid  furnace  is  fully  described  in  this  paper  and  the  funda- 
mental reaction  by  which  calcium  cyanamid  is  produced  is  given 
as  CaO  +  2C  +  2N  =  CaCN2  +  CO.  When  the  price  of  cal- 
cium carbid  fell  to  a  point  at  which  it  could  be  commercially  used 
it  was  found  that  the  production  of  calcium  cyanamid  was  more 
economically  secured  by  starting  with  the  carbid  itself.  The 
fundamental  reaction  in  this  case  is  CaC2-|-N2=CaCN2-(-C. 
The  principle  of  the  construction  of  the  cyanamid  furnace  is 
based  upon  the  utilization  of  a  series  of  coal-fired  retorts,  closed 
air-tight,  and  partially  filled  with  powdered  calcium  carbid.  After 
the  contents  of  the  retort  have  reached  a  white  heat  nitrogen  gas 
is  introduced  therein.  In  these  conditions  the  carbid  rapidly  ab- 
sorbs the  nitrogen.  The  reaction  is  exothermic  and  the  heat 
evolved  promotes  still  more  the  activity  of  the  combination.  Af- 
ter the  carbid  is  absorbed  by  the  nitrogen  the  incandescent  cyan- 
amid is  removed  from  the  retorts,  cooled  under  exclusion  of  the 
air  and  powdered  and  packed  for  shipping. 

The  commercial  calcium  cyanamid  is  a  black  powder,  quite 
stable  in  the  air  and  consists  of  57  per  cent,  of  calcium  cyanamid 
14  per  cent,  free  carbon,  to  which  the  black  color  is  due,  21  per 
cent,  caustic  lime,  2^2  per  cent,  of  silicic  acid,  four  per  cent,  of 
iron  oxid,  and  small  quantities  of  sulfur,  phosphorus  and  carbonic 
acid.  The  average  content  of  nitrogen  is  about  20  per  cent. 
When  placed  in  water  calcium  cyanamid  dissolves,  decomposing 
quickly,  especially  in  hot  water,  and  yielding  caustic  lime,  and, 
by  polymerization,  a  complicated  compound  called  dicyanamid. 
Subjected  to  overheated  steam  calcium  cyanamid  gives  off  its 
nitrogen  quantitatively  in  the  form  of  ammonia.  In  aqueous 
solution,  under  the  influence  of  certain  acids,  a  series  of  synthetic 
organic  compounds  are  produced,  among  which  is  found  urea. 


313  AGRICULTURAL   ANALYSIS 

When  fused  with  sodium  carbonate,  sodium  chlorid  or  other 
similar  materials,  all  of  the  nitrogen  in  the  cyanamid  is  converted 
into  cyanid  nitrogen,  in  other  words,  the  product  is  a  mixture 
of  calcium  cyanid,  and  sodium  cyanid.  Erlwein  draws  the 
following  conclusions  from  the  present  state  of  the  art : 

Cyanamid  may  be  used  directly  as  a  fertilizer  in  agricul- 
ture. Those  who  are  interested  in  the  agricultural  side  of  the 
problem  will  find  interesting  comparative  pictures  of  the  growth 
of  plants  under  the  fertilizing  action  of  Chile  saltpeter  and  cal- 
cium cyanamid,  etc.,  in  the  original  German  paper. 

2.  Calcium  cyanamid  may  be  used  for  the  production  of  ammo- 
nium sulfate,  which  is  also  consumed  in  large  quantities  for  fer- 
tilizing purposes.     The  reaction  yielding  ammonia  is  CaCN2+ 
3H20=CaCO3+2NH3. 

3.  Cyanamid  may  be  used  for  the  manufacture  of  dicyanamid, 
a  compound  used  in  the  manufacture  of  anilin  dyes  and  gun 
powder.       By  suitable  leaching  with  water  and  crystallization, 

this  compound  is  obtained  in  the  form  of  pretty  white  crystals.  The 
chemical  equation  is  2CaCN2+4H2O=2Ca(OH)2+(CNNH2)2. 

4.  Cyanamid  may  be  used  as  the  starting  material  for  the  com- 
mercial manufacture  of  sodium  cyanid  or  potassium  cyanid.     Ac- 
cording to  a  process   devised  by  Freudenberg,   the  calcium  is 
melted  with  sodium  chlorid  in  excess  and  is  thereby  transformed 
almost  completely  into  sodium  cyanid.     The  product  obtained  in 
this  way,  which  contains  about  22  to  23  per  cent,  of  sodium  cy- 
anid (corresponding  to  30  per  cent,  of  potassium  cyanid),  is  either 
sold  directly  in  this  form  as  so-called  "sodium-cyanid  substitute" 
(Cyannatrium-Surrogat)  for  use  in  gold  metallurgy,  or  is  worked 
up   into  chemically  pure   sodium   cyanid  or   potassium   cyanid. 
Both  brands  will  be  made  on  a  commercial  scale  as  soon  as  a 
new  factory  is  completed  which  is  in  course  of  erection  near 
Berlin. 

5.  As  a  hardening  material  for  iron  and  steel,  calcium  cyan- 
amid has  found  a  new  sphere  of  application.     This  application 
is  due  to  the  ability  of  the  cyanamid  to  give  off  carbon  to  the 
iron  which  is  thereby  hardened.     This  ability  is  enhanced  by  the 
addition  of  other  compounds  to  the  cyanamid  and  this  product  is 


PRODUCTION   OF   NITRIC  ACID  BY  ELECTRIC  ACTION  313 

now  sold  under  the  trade  name,  of  "Ferrodur."  Dr.  Reininger, 
chief  chemist  of  the  well-known  tool-steel  and  machine  works  of 
Ludwig  Loewe,  first  recognized  this  property  of  cyanamid  and 
called  attention  to  the  extremely  uniform  action  of  this  new 
hardening  material,  which  proves  useful  especially  at  such  tem- 
peratures at  which  a  uniform  introduction  of  carbon  into  iron 
heretofore  met  with  difficulties. 

6.  For  the  manufacture  of  urea  a  small  plant  is  already  in 
operation  in  which  the  calcium  cyanamid  is  treated  in  a  suitable 
way  with  acids  and  immediately  changed  into  solutions  of  urea, 
which  may  be  easily  crystallized. 

273.  Production  of  Nitric  Acid  by  Electric  Action. — This  sub- 
ject has  been  largely  studied  in  many  parts  of  the  world, 
and  in  this  country  at  Niagara  Falls  works  of  consid- 
erable magnitude  have  been  erected  for  the  production  of  nitric 
acid  under  electric  influence,  the  electric  power  being  generated 
by  the  water  of  Niagara  Falls.793 

The  Atmospheric  Product  Company  at  Niagara  Falls  installed 
upon  the  methods  of  Bradley  and  Lovejoy  gave,  at  first,  appar- 
ently satisfactory  results  per  kilowatt  in  the  production  of  nitric 
acid.  This  method,  however,  necessitated  apparatus  of  a  very 
complicated  character  in  order  to  insure  its  industrial  success. 
For  this  reason,  since  the  summer  of  1904  it  has  not  been  operated 
for  the  production  of  nitric  acid.  The  company  had  hoped  to 
utilize  1 5o,ooo-horse  power  furnished  by  Niagara  Falls, 
and  expected,  therefore,  to  make  a  sufficient  quantity  of 
nitrate  of  soda  for  the  world's  supply.  It  is  possible 
that  the  time  may  come  when  the  utilization  of  150,000- 
horse  power  will  accomplish  this  result,  but  the  experience  so 
far  obtained  at  Niagara  does  not  bear  out  the  hopes  of  its  im- 
mediate fulfilment.  While  these  experiments  were  conducted  at 
Niagara  Falls,  Kowalski  and  Moscicki  built  a  factory  at  Fribourg 
for  the  manufacture  of  nitric  acid  by  electricity.  They  used 
alternating  currents  of  very  high  tension,  from  50  to  75  thou- 
sand volts.  The  electrodes  employed  were  of  aluminum.  This 
factory,  however,  does  not  appear  to  have  had  very  much 
greater  success  commercially  than  the  one  at  Niagara  Falls. 
79a  Grandean,  La  Production  £lectrique  de  1'Acide  nitrique,  1906. 


314  AGRICULTURAL,  ANALYSIS 

In  1903  an  improvement  in .  the  manufacture  of  nitric  acid 
from  the  atmosphere  was  made  by  Birkeland  and  Eyde.  Birke- 
land  employed  a  continuous  current  produced  by  40  amperes  at 
600  volts,  which,  in  connection  with  other  principles  of  the  method, 
produced  a  magnetic  field  of  very  great  intensity.  This  led  to  the 
invention  and  establishment  of  the  apparatus  which  has  been 
erected  at  Notodden,  Norway.  The  furnaces  now  constructed  com- 
prise three  of  identical  structure.  The  energy  of  the  furnace  has 
been  carried  from  500  to  700  kilowatts,  that  is  from  700  to  1000 
horse  power,  for  each  of  them.  It  has  been  possible,  in  the  very 
latest  experiments  to  increase  the  energy  of  these  furnaces  to  1500 
horse  power.  It  is  found,  however,  that  the  furnaces  work  more  ef- 
fectually and  give  better  results  at  a  uniform  utilization  of  from 
500  to  600  kilowatts.  The  electric  energy  necessary  for  the  work- 
ing of  the  factory  at  Notodden  is  furnished  at  a  price  of  32  francs 
per  kilowatt-year.  The  electricity  is  furnished  by  a  generator 
of  two  thousand  kilowatts  capacity  of  a  triphase  construction  and 
at  a  tension  of  5000  volts.  The  air  sent  into  the  furnace  by  the 
ventilators  is  used  up  at  the  rate  of  25,000  liters  per  minute  for 
each  one,  that  is  for  the  three  furnaces  75,000  liters  per  minute.  It 
at  once  reaches  the  magnetic  field  formed  by  the  wall  of  the  fur- 
nace made  of  fire  clay.  The  air  mixed  with  the  nitric  gas  pro- 
duced in  the  furnace  leaves  the  apparatus  through  a  tube  kept 
at  a  temperature  of  from  500°  to  700°,  a  temperature  much 
higher  than  that  in  other  apparatus  destined  to  produce  nitric  acid. 
The  gases  pass  first  through  a  tubular  boiler  where  they  are  cooled 
to  about  200°.  The  steam  which  is  produced  in  this  boiler 
is  utilized  in  the  concentration  of  the  solutions  of  nitrate  of  lime 
which  are  finally  formed.  From  this  boiler  the  gases  are  intro- 
duced into  the  cooling  apparatus  which  rapidly  reduces  their  tem- 
perature to  50°  or  60°,  a  temperature  which  is  the  most 
favorable  to  the  reactions  which  result  in  the  formation  of  nitrous 
acid.  In  the  magnetic  field  of  the  furnace  it  should  be  under- 
stood that  there  is  formed  only  a  single  nitrogen  combination ; 
namely,  oxid  of  nitrogen  NO.  Its  proportion  reaches  about 
five  per  cent,  of  the  total  volume  of  gas.  At  a  very  high  tempera- 
ture of  from  2000°  to  2500°  the  elements  of  this  oxid  are  separa- 


ABSORPTION    TOWERS  315, 

ted  and  recombined  incessantly  in  such  a  way  that  the  total 
percentage  of  the  oxid  of  nitrogen  remains  constant  in  the  mix- 
ture. 

274.  Oxidation  Towers. — These  large  reservoirs  communicate 
with  the  electric  furnaces  by  large  tubes  and  are  two  in  number. 
They  are  cylindrical  in  shape  and  in  the  interior  are  covered  by 
a  material  which  is  not  attacked  by  acids.     In  these  towers  the 
further  oxidation  of  the  oxid  of  nitrogen  produced  in  the  furnace 
takes  place.     In  a  short  time  in  these  towers  the  oxid  of  nitrogen 
(NO)  is  converted  into  NO2.  Leaving  the  reservoirs,  the  nitrous 
gas  produced  is  forced  through  a  ventilator  into  the  absorption 
lowers  where  it  is  transformed  into  nitric  acid.     The  transforma- 
tion which  takes  place  in  these  last  towers,  converts  the  nitrous 
oxid  into  nitric  acid  by  means  of  water  according  to  the  formula, 
2NO2+H2O=HNO3-f  HNO2.    At  the  same  time  that  the  nitric 
and  nitrous  acids  are  formed  there  are  produced  lower  oxids  of 
nitrogen  by  the  decomposition  of  nitrous  acid  according  to  the 
following  equation:  2HNO2=NO2-f NO+H2O.     These  are  re- 
oxidized  by  the  continuous  fundamental  reaction. 

275.  Absorption  Towers. — These  are  prismatic  in  shape,  having 
a  section  four  meters  square  and   10  meters  high.     They  con- 
tain, therefore,  40  cubic  meters.    They  are  placed  along  the  sides 
of  a  hall  in  two  parallel  rows,  each  row  embraces  two  towers  in 
granite  and  two  towers  in  sandstone,  filled  with  pieces  of  quartz 
of  the  size  of  the  thumb,  two-thirds  of  their  height.     In  the  in- 
terior of  these  towers  there  are  circulated  in  an  inverse  direc- 
tion and  in  a  continuous  manner  the  gases  and  the  water.     This 
water,   which   constantly  moistens  the  quartz,   is   charged  pro- 
gressively with  the  nitric  acid  which  is  formed.    The  other  nitrous 
products,  with  the  exception  of  the  lower  oxids,  which  accompany 
the  formation  of  nitrous  acid,  are  reoxidized  in  these  towers  in 
contact  with  the  oxygen  of  the  air,  and  give  new  quantities  of 
nitrous  acid,  as  has  just  been  described.     Finally,  when  the  solu- 
tion of  nitric  acid  produced  in  the  towers  has  attained  by  re- 
peated contact  with  the  gases  and  water  a  concentration  of  50 
per  cent.,  that  is,  50  kilograms  of  monohydrated  nitric  acid  in 
100  liters  of  liquid,  it  is  received  into  ordinary  vessels  made  of 


AGRICULTURAL   ANALYSIS 

granite  and  provisionally  stored  therein.  From  the  towers  in 
which  the  water  and  gases  coming  from  the  oxidation  towers 
are  circulated  in  an  inverse  direction,  there  is  obtained  the 
greatest  part  of  the  nitrate  product  transferred  into  monohydrate 
nitric  acid  and  dissolved  in  water.  It  is,  however,  very  import- 
ant not  to  permit  the  loss  of  the  nitric  products  which  have  es- 
caped absorption  in  the  system  of  towers  and  are  found  in  nota- 
ble quantities  in  the  gases  escaping  from  the  last  one  of  the  ves- 
sels. In  order  to  collect  these  gases  an  energetic  absorbent  is 
used,  namely,  milk  of  lime.  For  this  purpose  there  is  a  fifth  tower 
of  wood  of  the  same  dimensions  as  the  first  four,  and  this  is  filled 
with  bricks  disposed  in  layers  and  over  which  circulates,  method- 
ically distributed,  the  milk  of  lime.  The  nitrous  and  nitric  gases 
are  retained  by  the  lime  and  produce  a  mixture  of  nitrite  and 
nitrate  of  lime.  This  mixture  is  afterwards  broken  up  by  the 
aid  of  nitric  acid  into  the  nitrate  of  lime  and  gaseous  nitrous  oxid, 
which  is  reintroduced  into  the  absorbent  system  in  the  manner 
which  has  already  been  described.  This  breaking  up  of  the  com- 
pound by  means  of  nitric  acid  is  expressed  by  the  following  equa- 
tion :  ( CaNCX )  2+HNO3=  ( CaNO3 )  2+H2O-f  NO2+NO. 

Finally,  in  order  to  complete  the  operation  and  retain  the  rest 
of  the  nitric  gases  which  still  escape  from  the  milk  of  lime  vessel, 
these  gases  are  made  to  traverse  another  vessel  somewhat 
smaller  in  dimension  than  the  other  and  containing  quicklime. 
It  is  only  in  escaping  from  this  last  vessel  that  the  gases  which 
have  traversed  the  whole  system  of  oxidation  since  their  entry 
into  the  electric  furnace  are  allowed  to  escape  into  the  atmos- 
phere. The  operations  which  have  just  been  described  permit 
the  final  transformation  into  pure  nitric  acid  of  50  per  cent, 
strength,  of  at  least  95  per  cent,  of  the  oxid  of  nitrogen  produced 
in  the  electric  furnace,  a  remarkable  result  for  an  industrial  opera- 
tion. 

276.  Manufacture  of  Nitrate  of  Lime. — The  solution  of  pure 
nitrate  of  lime,  coming  from  the  decomposition  of  mixtures  of 
nitrates  and  nitrites  described  above,  is  conducted,  together  with 
the  pure  nitric  acid  of  50  per  cent,  strength,  into  a  row  of  open 
vessels  of  granite  containing  pieces  of  carbonate  of  lime  of  from 


MANUFACTURE   OF   NITRATE   OF    LIME  317 

13  to  20  centimeters  in  diameter.  The  carbonate  of  lime  is  em- 
ployed in  quantities  suitable  to  neutralize  completely  the  acid 
solution  and  to  produce  neutral  nitrate  of  lime.  This  operation 
is  conducted  methodically  in  four  superimposed  vessels.  Upon 
the  fresh  carbonate  the  solution  which  has  been  almost  neutralized 
is  brought.  The  fresh  acid  is  placed  in  contact  with  the  residue 
of  lime  which  has  not  been  dissolved  by  the  first  treatments  with 
the  partially  saturated  solution.  By  reason  of  their  superposition 
the  movement  of  the  liquid  in  the  vessels  is  operated  automat- 
ically. Finally,  there  is  obtained  a  solution  of  neutral  nitrate  of 
lime  which  is  conducted  into  evaporation  vessels.  The  concen- 
tration of  the  liquid  is  accomplished  partially  by  the  aid  of  steam 
coming  from  the  boiler  used  for  the  cooling  of  gases  escaping 
from  the  electric  furnace,  as  has  been  previously  described,  and 
partially  in  a  direct  manner.  The  solution  of  nitrates  is  reduced 
to  such  a  concentration  that  their  boiling  point  rises  to  145°, 
which  gives  a  liquid  containing  from  75  to  80  per  cent,  of  nitrate 
•of  lime,  equivalent  to  from  15.2  to  15.5  per  cent,  of  nitrogen. 
This  viscous  mixture  is  poured  into  vessels  of  200  liters  capacity 
and  allowed  to  solidify  by  cooling.  The  nitrate  can  be  shipped 
•either  in  this  state  or  after  powdering. 

Instead  of  evaporating  the  nitrate  of  lime  until  the  liquid 
has  obtained  a  boiling  point  of  145°,  it  may  be  allowed  to  crys- 
tallize after  having  been  evaporated  to  120°  only.  The  crystals  of 
nitrate  of  lime  are  then  separated  in  a  centrifugal.  Finally  there 
is  manufactured  at  Notodden  some  basic  nitrate  of  lime  by 
adding  to  the  hot  solution  a  proper  proportion  of  quicklime. 
After  cooling,  the  product  is  broken  up  and  passed  through  a 
.sieve.  The  basic  nitrate  contains  about  10  per  cent,  of  nitrogen. 
It  goes  without  saying  that  by  the  process  just  described  there 
-can  also  be  manufactured  nitrate  of  soda,  or  potash,  in  place  of 
nitrate  of  lime.  It  is  the  cheapness  of  the  lime,  however,  as  com- 
pared with  soda  which  has  led  the  manufacturers  at  Notodden 
to  transform  the  nitric  acid  into  calcium  nitrate. 

The  actual  production  of  nitric  acid  at  Notodden  amounts  to 
from  500  to  600  kilograms  per  kilowatt->  ear.  The  factory,  which 
lias  been  running  since  the  2d  of  May,  1905,  has  produced  in  one 


AGRICULTURAL  ANALYSIS 

year  730,000  kilograms  of  monohydrate  nitric  acid.  The  success 
of  this  enterprise,  which  has  been  so  anxiously  awaited  throughout 
the  whole  world,  should  lead  the  farmers  of  the  world  to  enter- 
tain the  hope  that  even  if  the  stores  of  nitric  acid  in  Chile  and 
other  localities  are  exhausted  there  can  be  created  a  supply  of 
this  material,  which  may  be  said  to  be  unlimited,  obtained  from 
the  air  and  offered  from  an  inexhaustible  source,  not  only  for 
agricultural  needs,  but  also  other  industrial  needs  of  man. 

It  is  not  likely  that  this  process  of  Birkeland  and  Eyde  has 
yet  reached  its  limit  of  perfection.  There  is  no  reason  why 
some  similar  process  might  not  be  conducted  in  connection  with 
the  great  waterfalls  of  this  country,  which  would  lead  to  a  sup- 
ply of  nitric  acid  even  at  a  lower  price  than  can  now  be  secured 
from  natural  stores. 

277.  Absorption  of  Nitric  Acid  and  Concentration  of  the  Product. 
—This  subject  is  discussed  still  further  by  Howies,  espe- 
cially in  regard  to  the  direct  oxidation  of  nitric  acid  in  the  air  by 
means  of  electric  discharges  and  the  production  of  nitric  acid 
therefrom  without  the  intervention  of  the  calcium  compounds. 
The  conclusions  reached  by  Howies  in  regard  to  this  method 
of  producing  nitric  acid  are  as  follows  :80 

After  leaving  the  furnace,  the  air  contains  about  two  per  cent. ' 
by  volume  of  nitric  oxid,  which  becomes  rapidly  converted,  by 
means  of  the  excess  oxygen  present  into  nitrogen  peroxid. 
The  mixed  gases  then  pass  on  to  absorption  towers,  which  present 
no  special  features  of  construction  and  down  which  water  or 
dilute  acid  flows.  In  the  case  of  the  last  tower,  milk  of  lime  is 
used,  as  it  is  difficult  to  absorb  the  last  traces  of  NO2  by  means 
of  water  alone.  By  this  process  there  is  obtained  an  acid  of 
not  more  than  50  per  cent,  strength. 

The  preparation  of  a  concentrated  nitrous-free  acid  from  the 
nitrous  gases  constitutes  one  of  the  most  serious  problems  in 
connection  with  this  process.  The  reaction  represented  by  this 
equation,  viz.,  2NO2-f-O-j-H2O=2HNO3,  does  not  take  place 
in  the  absorption  towers;  such  an  equilibrium  appears  to  exist 
only  in  the  gaseous  state.  On  condensation  the  right-hand  side 
80  Electrochemical  and  Metallurgical  Industry,  1907,  5  :  358. 


ABSORPTION  OF  NITRIC  ACID  319 

of  the  equation  is  not  produced.  The  most  concentrated  acid 
which  has  so  far  been  obtained  by  the  condensation  of  nitrous 
gases  in  water  in  the  presence  of  oxygen  corresponds  to  the  for- 
mula HNO3,  2H2O,  and  possesses  a  density  of  40.6°  B.,  repre- 
senting 63.63  per  cent,  of  anhydrous  nitric  acid.  The  forma- 
tion of  this  acid  takes  place,  according  to  the  following  equation, 
in  the  Lunge  and  Rohrmann  plate  towers : 

2NO2+O+5H2O=2(HNO3,  2H,O), 

from  which  acid  of  40°  to  41°  B.  is  obtained.  By  passing  the 
gases,  however,  through  towers  down  which  water  flows,  an 
equimolecular  mixture  of  nitric  and  nitrous  acids  results,  which 
at  the  most,  can  not  attain  a  concentration  greater  than  that 
obtained  in  the  Lunge  towers.  Attempts  at  further  concentra- 
tion by  the  passage  of  nitrogen  peroxid  through  the  solution, 
simply  result  in  an  increase  of  nitric  acid  at  the  expense  of  the 
nitrous.  The  strongest  acid  is  thus  never  free  from  nitrous 
acid,  and  each  succeeding  absorption  tower  contains  less  and 
less  nitric  acid,  while  at  the  same  time  the  nitrous  acid  in- 
creases, for  as  the  free  oxygen  in  the  gases  becomes  consumed 
the  NO  and  NO2  tend  to  react  as  N2O3,  yielding  only  nitrous 
acid.  It  is  not  possible  to  prepare  much  stronger  acid  by  frac- 
tionating the  50  per  cent,  acid  from  the  first  absorption  tower, 
since  a  product  of  minimum  vapor  pressure,  boiling  at  120°, 
and  containing  68  per  cent,  of  anhydrous  acid,  is  obtained  as 
residue. 

Thus  in  order  to  prepare  the  most  concentrated  acid  by  the 
nitrogen  combustion  process  it  would  be  necessary  to  either 
add  the  50  per  cent,  acid  to  concentrated  sulfuric  acid  until  a 
dilution  of  say  54°  B.,  is  obtained  (54°  B.  equals  120°  Tw. 
equals  68.5  per  cent,  of  H2SO4),  and  distill  the  nitric  acid;  or  to 
prepare  a  salt  of  nitric  acid,  and  distill  in  the  usual  way  with 
sulfuric  acid  or  a  bisulfate. 

An  electrolytic  method  for  concentrating  and  oxidizing  the 
weak  tower  acid  has  lately  been  patented.  The  process  con- 
sists in  refrigerating  the  oxids  of  nitrogen  evolved  during  elec- 
trolysis at  the  cathode,  and  leading  them  in  the  liquid  state  slow- 
ly to  the  anode  compartment  of  the  -cell,  where  in  presence  of 


32O  AGRICULTURAL  ANALYSIS 

the  nascent  oxygen  there  generated,  a  solution  of  pure  nitric  acid 
results,  all  nitrous  acid  undergoing  oxidation.  It  is  not  stated 
if  this  process  has  proved  a  commercial  success. 

Thus,  although  the  electrochemical  production  of  nitric  acid 
has  attained  a  fair  degree  of  efficiency  in  some  of  the  processes 
described,  the  problem  of  directly  manufacturing  a  98  per  cent, 
acid  from  the  furnace  gases  has  not  yet  been  solved. 

278.  Method  of  Moscicki. — A  further  contribution  to  this  in- 
teresting subject  from  an  agricultural  point  of  view  has  been 
made  by  Moscicki.81     In  the  system  of  Moscicki  the  principle  of 
the  magnetic   deflection  of   the  arc   is   used.     The  study   of   a 
quiet  flame  shows  different  zones  within  the  flame.     Only  the 
hottest  zone  is   used   for  the  oxidation   of  the   nitrogen.     The 
oxidized   nitrogen   which   is  produced   within  this   hot  zone   is 
more  or  less  decomposed  in  passing  into  the  parts  of  the  arc 
of  lower  temperature.     The  important  modification  of  Moscicki,. 
therefore,  consists  in  suppressing  these  cooler  areas,  and  this  is 
accomplished  by  a  magnetic  deflection  of  the  flame.     The  mag- 
netic attraction  only  sets  those  parts  of  the  flame  into  motion 
which  carry  the  electric  current,  while  on  account  of  the  rapidity 
of  the  motion  the  influence,  of  the  cooler  zones  is  eliminated. 

279.  Production  of  Nitric  Acid  in  the  United  States  from  At- 
mospheric Nitrogen. — The  present  status  of  the  industries  relat- 
ing to  the  oxidation  of  atmospheric  nitrogen  and  the  produc- 
tion of  nitric  acid,  or  some  similar  product  therefrom,  in  the 
United  States  may  still  be  described  as  a  waiting  one.     There 
is  no  doubt  of  the  importance  of  the  problem  under  considera- 
tion, especially  to  agriculture,  but  the  actual  economical  devel- 
opment  of   the   industry    is    still   in   the   future.     Two   general 
methods  of  experimental  work  have  been  followed.     One  class 
of  experiments  looks  to  the  use  of  electric  discharges  through 
the  air  in  order  to  produce  the  oxidation  of  the  nitrogen  and 
form   the   first   products,  which   afterwards   may   be   developed 
into  nitric  acid.82 

As  has  been  before  intimated  the  electric  plant  established  at 

81  Electrochemical  and  Metallurgical  Industry,  1907,  5  :  491- 
M  Electrochemical  and  Metallurgical  Industry,  1907,  5  :  289. 


CLASSIFICATION  OF  METHODS  321 

Niagara  Falls  for  the  production  of  nitric  acid  from  the  air 
has  been  abandoned.  The  success  of  the  experiments  in  Norway 
is  promising,  but  attention  is  called  to  the  fact  that  the  process 
in  Norway  utilizes  the  moving  arc  method  instead  of  the  old 
spark  method,  and  is  dependent  essentially  on  the  exceedingly 
low  prices  of  electric  power  in  that  country. 

The  second  method  of  utilizing  the  atmospheric  nitrogen, 
which  is  now  under  investigation,  is  that  which  starts  with  cal- 
cium carbid,  the  product  of  the  electric  furnace,  and  treats 
this  compound  later  with  nitrogen  in  such  a  way  as  to  produce 
the  calcium  cyanamid.  A  company  has  been  formed  in  the 
United  States  to  operate  a  factory  upon  the  above  principle,  and 
it  is  proposed  to  erect  a  plant  of  20,000  metric  tons  annual 
capacity  on  the  Tennessee  River  in  Northern  Alabama.  In  this 
locality  there  is  abundant  and  cheap  water  power,  as  well  as 
coal  •  and  coke.  Labor  is  also  abundant  and  reasonably  cheap. 
The  Tennessee  River  also  furnishes  water  transportation  of  the 
cheapest  character.  It  is  near  some  of  the  great  phosphate 
deposits,  so  that  in  the  manufacture  of  the  complete  fertilizers 
a  large  part  of  the  material  would  be  derived  from  the  same 
localities. 

METHODS  OF  ANALYSIS 

280.  Classification  of  Methods. — In  case  a  microscopic  exam- 
ination of  the  sample  is  required  it  should  precede  the  chemical 
operations.  In  general,  there  are  three  direct  methods  of  deter- 
mining the  nitrogen  content  of  fertilizers.  First  the  nitrogen 
may  be  secured  in  a  gaseous  form  and  the  volume  thereof,  under 
standard  conditions,  measured  and  the  weight  of  nitrogen  com- 
puted. This  process  is  commonly  known  as  the  absolute  method. 
Practically  it  has  passed  out  of  use  in  fertilizer  work,  or  is  prac- 
ticed only  as  a  check  against  new  and  untried  methods,  or  on 
certain  nitrogenous  compounds  which  do  not  readily  yield  all 
their  nitrogen  by  the  other  methods.  The  process,  first  perfected 
by  Dumas,  whose  name  it  bears,  consists  in  the  combustion  of 
the  nitrogenous  body  in  an  environment  of  copper  oxid,  by  which 
the  nitrogen,  by  reason  of  its  inertness,  is  left  in  a  gaseous  state 
ii 


322  AGRICULTURAL   ANALYSIS 

after  the  oxidation  of  the  other  constituents;  viz.,  carbon  and 
hydrogen,  originally  present. 

In  the  second  class  of  methods  the  nitrogen  is  converted  into 
ammonia,  which  is  absorbed  by  an  excess  of  standard  acid,  the 
residue  of  which  is  .determined  by  subsequent  titration  with  a 
standard  alkali.  There  are  two  distinct  processes  belonging  to 
this  class,  in  one  of  which  ammonia  is  directly  produced  by  dry 
combustion  of  an  organic  nitrogenous  compound  with  an  alkali, 
and  in  the  other  ammonium  sulfate  is  produced  by  moist  com- 
bustion with  sulfuric  acid,  and  the  salt  thus  formed  is  subse- 
quently distilled  with  an  alkali  and  the  free  ammonia  resulting 
therefrom  estimated  as  above  described.  Nitric  nitrogen  may 
also  be  reduced  to  ammonia  by  nascent  hydrogen  either  in  an 
acid  or  alkaline  solution. 

In  the  third  class  of  determinations  is  included  the  estimation  of 
nitric  nitrogen  by  colorimetric  methods.  These  processes  have 
little  practical  value  in  connection  with  the  analyses  of  com- 
mercial fertilizers,  but  find  their  chief  use  in  the  detection  and 
estimation  of  extremely  minute  quantities  of  nitrites  and  nitrates. 
In  the  following  paragraphs  will  be  given  the  standard  methods 
for  the  determination  of  nitrogen  in  practical  work  with  fertiliz- 
ing materials  and  fertilizers,  and  also  the  methods  for  the  esti- 
mation of  minute  quantities  of  ammoniacal  and  nitric  nitrogen. 

281.  Determination  of  the  State  of  Combination. — Some  of 
the  sample  is  mixed  with  a  little  powdered  soda-lime.  If  am- 
moniacal nitrogen  be  present  free  ammonia  is  evolved  even  in 
the  cold  and  may  be  detected  either  by  its  odor  or  by  testing 
the  escaping  gas  with  litmus  or  turmeric  paper.  A  glass  rod 
moistened  with  strong  hydrochloric  acid  will  produce  white 
fumes  of  ammonium  chlorid  when  brought  near  the  escaping 
ammonia. 

If  the  sample  contain  any  notable  amount  of  nitric  acid  it  will 
be  revealed  by  treating  an  aqueous  splution  of  it  with  a  crystal 
of  ferrous  suifate  and  strong  sulfuric  acid.  The  iron  salt  should 
be  placed  in  a  test-tube  with  a  few  drops  of  the  solution  of  the 
fertilizer  and  the  sulfuric  acid  poured  down  the  sides  of  the  tube 
in  such  a  way  as  to  run  under  and  not  to  mix  with  the  other 


OFFICIAL    METHODS  323 

liquids.  The  tube  must  be  kept  cold.  A  dark  brown  ring  will  mark 
the  disk  of  separation  between  the  sulfuric  acid  and  the  aqueous 
solution  in  case  nitric  acid  be  present.  If  water  produces  a 
solution  of  the  sample  too  highly  colored  to  be  used  as  above, 
alcohol  of  80  per  cent,  strength  may  be  substituted.  The  colora- 
tion produced  in  this  case  is  of  a  rose  or  purple  tint. 

Nitric  nitrogen  may  also  be  detected  by  means  of  brucin.  If 
a  few  drops  of  an  aqueous  solution  of  brucin  be  mixed  with  the 
same  quantity  of  an  aqueous  extract  of  the  sample  under  exam- 
ination and  strong  sulfuric  acid  be  added,  as  described  above, 
there  will  be  developed  at  the  disk  of  contact  between  the  acid 
and  the  mixed  solutions  a  persistent  rose  tint  varying  to  yellow. 

To  detect  the  presence  of  albuminoid  nitrogen  the  sample  is 
exhausted  with  water  and  heated  with  soda-lime,  which  gives 
rise  to  ammonia  which  may  be  detected  as  described  above. 

282.  Microscopic    Examination. — If   the    chemical    test    reveal 
the  presence  of  organic  nitrogen,  the. next  point  to  be  determined 
is  the  nature   of  the   substance   containing  it.       Often   this   is 
revealed  by  simple  inspection,  as  in  the  case  of  cottonseed-meal. 
JKrequently,  however,  especially  in  cases  of  finely  ground  mixed 
goods,  the  microscope  must  be  employed  to  determine  the  charac- 
ter   of    the    organic    matter.     It  is  important  to  know  whether 
hair,  horn,  hoof,  and  other  less  valuable  forms  of  nitrogenous 
compounds  have  been  substituted,  for  dried  blood,  tankage,  and 
more  valuable  forms.     In  most  cases  the  qualitative  chemical,  and 
microscopic  examination  will  be  sufficient.     There  may  be  cases, 
however,  where  the  analyst  will  be  under  the  necessity  of  using 
other  means  of  identification  suggested  by  his  skill  and  expe- 
rience or  by  the  circumstances  connected  with  any  particular  in- 
stance.    In  such  cases  the  general  appearance,  odor,  and  consis- 
tence of  the  sample  may  afford  valuable  indications  which  will 
aid  in  discovering  the  origin  of  the  nitrogenous  materials. 

283.  Official   Methods. — The   methods   adopted  by  the   Asso- 
ciation of  Official  Agricultural   Chemists   have   been   developed 
by  more  than  20  years  of  co-operative  work  on  the  part  of  the 
leading  agricultural  chemists  of  the  United  States.    These  meth- 
ods should  be  strictly  followed  in  all  essential  points  by  all  analysts 


324  AGRICULTURAL  ANALYSIS 

in  cases  where  comparison  with  other  data  is  concerned.  Future 
experience  will  doubtless  improve  the  processes  both  in  respect 
of  accuracy  and  simplicity,  but  it  must  be  granted  that,  as  at 
present  practiced,  they  give  essentially  accurate  results. 

284.  Volumetric  Estimation  by  Combustion  with  Copper  Oxid. 
— This  classical  method  of  analysis  is  based  on  the  principle,  that 
by  the  combustion  of  a  substance  containing  nitrogen  in  copper 
oxid  and  conducting  the  products  of  the  oxidation  over  red-hot 
copper  oxid  and  metallic  copper,  all  of  the  nitrogen  present  in 
whatever  form  will  be  obtained  in  a  free  state  and  can  subse- 
quently be  measured  as  a  gas.     The  air  originally  present  in  all 
parts  of  the  apparatus  must  first  be  removed  either  by  a  mer- 
cury pump  or  by  carbon  dioxid,  or  by  both  together,  the  resid- 
ual carbon  dioxid  being  absorbed  by  a  solution  of  caustic  alkali. 
Great  delicacy  of  manipulation  is  necessary  to  secure  a  perfect 
vacuum,  and,  as  a  rule,  a  small  quantity  of  gas  may  be  measured 
other  than  nitrogen,  so  that  the  results  of  the  analyses  are  often 
a  trifle  too  high.     The  presence  of  another  element  associated 
with  mtrogen,  or  the  possible  allotropic  existence  of  that  ele- 
ment, may  also  prove  to  be  a  disturbing  factor  in  this  long  prac- 
ticed, analytical  process.  For  instance,  if  nitrogen  be  contaminated 
with  another  element,  e.  g.,  argon,  of  a  greater  density,  the  com- 
monly accepted  weight  of  a  liter  of  nitrogen  is  too  great  and 
tables  of  calculation  based  on  that  weight  would  give  results 
too  high. 

First  will  be  given  the  official  method  for  this  process,  fol- 
lowed by  a  few  simple  variations  thereof,  as  practiced  in  the 
laboratory  of  the  Bureau  of  Chemistry. 

285.  The  Official  Volumetric   Method.— This   process   may  be 
used  for  nitrogen  in  any  form  of  combination.     Practically,  it  is 
no  longer  used  in  fertilizer  analysis,  but  the  method  is  inserted 
here  because  of  its  historic  and  scientific  value. 

The  apparatus  and  reagents  needed  are  as  follows : 
Combustion  tube  of  best  hard  Bohemian  glass,  about  66  centi- 
meters long  and  12.7  millimeters  internal  diameter. 

Asotometer  of  at  least  100  cubic  centimeters  capacity,  accu- 
rately calibrated. 


OFFICIAL   VOLUMETRIC    METHOD  325 

Sprengel  mercury  air-pump. 

Small  paper  scoop,  easily  made  from  stiff  writing  paper. 

Coarse  cupric  oxid,  to  be  ignited  and  cooled  before  using. 

Fine  cupric  oxid,  prepared  by  grinding  ordinary  cupric  oxid 

Metallic  copper,  granulated  copper,  or  fine  copper  gauze, 
heated  and  cooled  in  a  current  of  hydrogen. 

Sodium  bicarbonate,  free  from  organic  matter. 

Caustic  potash  solution,  a  supersaturated  solution  of  caustic 
potash  in  hot  water.  When  absorption  of  carbon  dioxid  during 
the  combustion  ceases  to  be  prompt,  the  solution  must  be  re- 
placed with  a  fresh  portion. 

Filling  the  tube. — Use  from  one  to  two  grams  of  ordinary 
commercial  fertilizers.  In  the  case  of  highly  nitrogenized  sub- 
stances, the  amount  to  be  used  must  be  regulated  by  the  amount 
of  nitrogen  estimated  to  be  present.  Fill  the  tube  as  follows:  (i) 
About  five  centimeters  of  coarse  cupric  oxid.  (2)  Place  on  the 
small  paper  scoop  enough  of  the  fine  cupric  oxid  to  fill,  after 
having  been  mixed  with  the  substance  to  be  analyzed,  about  10 
centimeters  of  the  tube ;  pour  on  this  the  substance,  rinsing  the 
watch-glass  with  a  little  of  the  fine  oxid,  and  mix  thoroughly 
with  a  spatula;  pour  into  the  tube,  rinsing  the  scoop  with  a  little 
fine  oxid.  (3)  About  30  centimeters  of  coarse  cupric  oxid.  (4) 
About  seven  centimeters  of  metallic  copper.  (5)  About  six 
centimeters  of  coarse  cupric  oxid  (anterior  layer).  (6)  A 
small  plug  of  asbestos.  (7)  From  eight-tenths  to  one  gram  of 
sodium  bicarbonate.  (8)  A  large,  loose  plug  of  asbestos.  Place 
the  tube  in  the  furnace,  leaving  about  two  and  five-tenths  centi- 
meters of  it  projecting;  connect  with  the  pump  by  a  rubber  stop- 
per smeared  with  glycerol,  taking  care  to  make  the  connection 
perfectly  tight. 

Operation. — Exhaust  the  air  from  the  tube  by  means  of  the 
pump.  When  a  vacuum  has  been  obtained,  allow  the  flow  of 
mercury  to  continue;  light  the  gas  under  that  part  of  the  tube 
containing  the  metallic  copper,  the  anterior  layer  of  cupric  oxid 
(see  (5)  above),  and  the  sodium  bicarbonate.  As  soon  as  the 
vacuum  is  destroyed  and  the  apparatus  filled  with  carbon  dioxid, 
shut  off  the  flow  of  mercury  and  at  once  introduce  the  delivery 


326  AGRICULTURAL   ANALYSIS 

tube  of  the  pump  into  the  receiving  arm  of  the  azotometer  just 
below  the  surface  of  the  mercury  seal,  so  that  the  escaping  bub- 
bles will  pass  into  the  air  and  not  into  the  tube,  thus  avoiding 
the  useless  saturation  of  the  caustic  potash  solution. 

When  the  flow  of  carbon  dioxid  has  very  nearly  or  completely 
ceased,  pass  the  delivery  tube  down  into  the  receiving  arm,  so  that 
the  bubbles  will  escape  into  the  azotometer.  Light  the  gas  under 
the  30  centimeter  layer  of  oxid,  heat  gently  for  a  few  moments  to 
drive  out  any  moisture  that  may  be  present,  and  bring  to  a  red 
heat.  Heat  gradually  the  mixture  of  substance  and  oxid,  lighting 
one  jet  at  a  time.  Avoid  a  too  rapid  evolution  of  bubbles,  which 
should  be  allowed  to  escape  at  the  rate  of  about  one  per  second 
or  a  little  faster. 

When  the  jets  under  the  mixture  have  all  been  turned  on, 
light  the  gas  under  the  layer  of  oxid  at  the  end  of  the  tube. 
When  the  evolution  of  gas  has  ceased,  turn  out  all  the  lights 
except  those  under  the  metallic  copper  and  anterior  layer  of 
cxid,  and  allow  to  cool  for  a  few  moments.  Exhaust  with  the 
pump  and  remove  the  azotometer  before  the  flow  of  mercury  is 
stopped.  Break  the  connection  of  the  tube  with  the  pump,  stop 
the  flow  of  mercury,  and  extinguish  the  lights.  Allow  the  azo- 
tometer to  stand  for  at  least  an  hour,  or  cool  with  a  stream  of 
water  until  a  permanent  volume  and  temperature  have  been 
reached. 

Adjust  accurately  the  level  of  the  potassium  hydroxid  solution 
in  the  bulb  to  that  in  the  azotometer;  note  the  volume  of  gas, 
temperature,  and  height  of  barometer ;  make  calculation  as  xisual, 
or  read  results  from  tables. 

286.  Note  on  Official  Volumetric  Method.  —  The  determina- 
tion of  nitrogen  in  its  gaseous  state  by  combustion  with  copper 
oxid,  has  practically  gone  out  of  use  as  an  analytical  method 
The  official  chemists  rarely  use  it  even  for  control  work  on  sam- 
ples sent  out  for  comparative  analysis.  The  method  recom- 
mended differs  considerably  from  the  process  of  Jenkins  and 
Johnson,  on  which  it  is  based.  The  only  source  of  oxygen  in 
the  official  method  is  in  the  copper  oxid.  Hence  it  is  necessary 


THE   PUMP  327 

that  the  oxid  in  immediate  contact  with  the  organic  matter  be  in 
a  sufficiently  fine  state  of  subdivision,  and  that  the  substance 
itself  be  very  finely  powdered  and  intimately  mixed  with  the 
oxidizing  material.  Failure  to  attend  to  these  precautions  will 
bo  followed  by  an  incomplete  combustion  and  a  consequent  deficit 
in  the  volume  of  nitrogen  obtained. 

The  copper  oxid  before  using  is  ignited,  and  is  best  filled  into 
the  tube  while  still  warm  by  means  of  a  long  pointed  metal  scoop, 
or  other  convenient  method.  The  copper  spiral,  after  use,  is  re- 
duced at  a  red  heat  in  a  current  of  hydrogen,  and  may  thus  be 
used  many  times. 

287.  The  Pump. — Any  form  of  mercury  pump  which  will 
secure  a  complete  vacuum  may  be  used.  A  most  excellent  one 
can  be  arranged  in  any  laboratory  at  a  very  small  expense.  The 
pump  used  in  the  laboratory  of  the  Bureau  of  Chemistry  for 
many  years  answers  every  purpose,  and  costs  practically  nothing, 
being  made  out  of  old  material  not  very  valuable  for  other  use. 

The  construction  of  the  pump  and  its  use  in  connection  with 
the  combustion  tube  will  be  clearly  understood  from  the  follow- 
ing description : 

A  glass  bulb  I  is  attached,  by  means  of  a  heavy  rubber  tube 
carrying  a  screw  clamp,  to  the  glass  tube  A,  having  heavy  walls 
and  a  small  internal  diameter,  and  being  one  meter  or  more  in 
length.  The  tube  A  is  continu  d  in  the  form  of  a  U,  the  two 
arms  being  joined  by  very  heavy  rubber  tubing  securely  wired. 
The  ends  of  the  glass  tubes  in  the  rubber  should  be  bent  so  that 
they  come  near  together  and  form  the  bend  of  the  U,  the  rubber 
simply  holding  them  in  place.  This  is  better  than  to  have  the 
tube  continuous,  avoiding  danger  of  breaking.  A  three  way  tube, 
T,  made  of  the  same  kind  of  glass  as  A,  is  connected  by  one  arm, 
a,  with  the  manometer  B,  by  a  heavy  rubber  union  well  wired. 
The  union  is  made  perfectly  air-tight  by  a  tube  filled  with  mercury 
held  in  place  by  a  rubber  stopper.  The  middle  arm  of  the  tee, 
a',  is  expanded  into  a  bulb,  E,  branching  into  two  arms,  one  of 
which  is  connected  with  A  and  the  other  with  the  delivery  tube 
F,  by  the  mercury-rubber  unions,  MM',  just  described.  The  in- 


328 


AGRICULTURAL   ANALYSIS 


terior  of  the  bulb  E  should  be  of  such  a  shape,  as  to  allow  each 
drop  of  mercury  to  fall  at  once  into  F  without  accumulating  in 
large  quantity  and  being  discharged  in  mass.  The  third  arm  of 
the  tee,  a",  is  bent  upwards  at  the  end  and  passes  into  a  mercury 
sealing  tube,  D,  where  it  is  connected  by  means  of  a  rubber  tube 
with  the  delivery  tube  from  the  furnace.  The  flow  of  the  mer- 


Fig.  14.     Mercury  Pump  and  Azotometer. 

cury  is  regulated  by  the  clamp  C,  and  care  should  be  taken  that 
the  supply  does  not  get  so  low  in  I  as  to  permit  air  bubbles  to 
enter  A.  The  manometer  B  dips  into  the  tube  of  mercury  H. 
A  pump  thus  constructed  is  simple,  flexible,  and  perfectly  tight. 
The  only  part  which  needs  to  be  specially  made  is  the  three  way 
tube  T,  and  the  one  in  use  here  was  blown  in  our  own  laboratory. 
The  bent  end  of  the  delivery  tube  F  may  also  be  united  to  the  main 


VOLUMETRIC  METHOD  329 

tube  by  a  rubber  joint,  thus  aiding  in  inserting  it  into  the  V- 
shaped  nozzle  of  the  azotometer. 

The  azotometer  used  is  the  one  devised  by  Schiff  and  modified 
by  Johnson  and  Jenkins.83 

The  V  nozzles  may  be  got  separately  and  joined  to  any 
good  burette  by  a  rubber  tube.  The  water-jacket  is  not  neces- 
sary, but  the  apparatus  can  be  left  exposed  until  it  reaches  room 
temperature. 

Any  form  of  mercury  pump  capable  of  securing  a  vacuum 
may  be  used,  but  the  one  just  described  is  commended  by  sim- 
plicity, economy,  effectiveness,  and  long  use. 

288.  The  Pump  and  Combustion  Furnace. — The     pump     and 
combustion  furnace,  as  used  in  the  above  process,  are  shown  in 
Fig.  14.     The  pump  is  constructed  as  just  described,  and  rests  in 
a  wooden  tray  which  catches  and  holds  any  mercury  which  may 
be  spilled.     The  furnace  is  placed  under  a  hood  which  carries 
off  the  products  of  the  burning  gas  and  the  hot  air.     A  well 
ventilated  hood  is  an  important  accessory  to  this  process,  espe- 
cially when  it  is  carried  on  in  summer.     A  small  mercury  pneu- 
matic trough  catches  the  overflow  from  the  pump  and  also  serves 
to  immerse  the  end  of  the  delivery  tube  during  the  exhaustion 
of  the  combustion  tube. 

The  other  details  of  the  arrangement  and  connections  have 
been  sufficiently  shown  in  the  previous  paragraph. 

289.  Volumetric  Method  of  Bureau  of  Chemistry. — It  has  been 
found   convenient  to   vary   slightly   the   method   of   the   official 
chemists  in  the  following  respects:     The  tube  used  for  the  com- 
bustion is  made  of  hard  refractory  glass,  which  will  keep  its  shape 
at  a  high  red  heat.     It  is  drawn  out  and  sealed  at  one  end  after 
being  well  cleaned  and  dried.     It  should  be  about  80  centime- 
ters in  length  and  from  12  to  14  millimeters  in  internal  diameter. 
The  relative  lengths  of  the  spaces  occupied  by  the  several  con- 
tents of  the  tube  are  approximately  as  follows :     Sodium  bicar- 
bonate, two ;  asbestos,  three ;  coarse  copper  oxid,  eight ;  fine  copper 
oxid,  containing  sample,  16 ;  coarse  copper  oxid,  25  ;  spiral  copper 

M  American  Chemical  Journal,  1880-81,  2  :  27. 


33O  AGRICULTURAL   ANALYSIS 

gauze,  10  to  15;  copper  oxid,  eight;  and  asbestos  plug,  five  centi- 
meters, respectively. 

The  copper  oxid  should  be  heated  for  a  considerable  time  to 
redness  in  a  muffle  with  free  access  of  air  before  using,  and  the 
copper  gauze  be  reduced  to  pure  metallic  copper  in  a  current  of 
hydrogen  at  a  low  red  heat.  The  anterior  layer  of  copper  oxid 
serves  to  oxidize  any  hydrogen  that  may  have  been  occluded  by 
the  copper.  When  a  sample  is  burned  containing  all  or  a  con- 
siderable part  of  the  nitrogen  as  nitrates,  the  longer  piece  of  cop- 
per gauze  is  used. 

290.  The  Combustion. — The  tube  having  been  charged  and 
connected  with  the  pump,  it  is  first  freed  from  air  by  running  the 
pump  until  the  mercury  no  longer  rises  in  the  manometer.  The 
end  of  the  tube  containing  the  sodium  bicarbonate  is  then  gently 
heated,  so  that  the  evolution  of  carbon  dioxid  will  be  at 
such  a  rate,  as  to  slowly  depress  the  mercury  in  the  manome- 
ter, but  never  fast  enough  to  exceed  the  capacity  of  the  pump  to 
remove  it.  The  lamp  is  extinguished  under  the  sodium  car- 
bonate and  the  carbon  dioxid  completely  removed  by  means  of 
the  pump.  The  delivery  tube  is  then  connected^  with  the  azotom- 
eter,  and  the  combustion  tube  carefully  heated  from  the  front 
end  backwards,  the  copper  gauze  and  coarse  copper  oxid  being 
raised  to  a  red  heat  before  the  part  containing  the  sample  is 
reached.  When  the  nitrogen  begins  to  come  off,  its  flow  should 
be  so  regulated  by  means  of  the  lamps  under  the  tube,  as  to  be 
regular  and  not  too  rapid.  From  half  an  hour  to  an  hour  should 
be  employed  in  completing  the  combustion.  Since  most  sam- 
ples of  fertilizer  contain  organic  matter,  the  nitrogen  will  be 
mixed  with  aqueous  vapor  and  carbon  dioxid.  The  former  is  con- 
densed before  reaching  the  azotometer,  and  the  latter  is  absorbed 
by  the  potassium  hydroxid.  When  the  sample  is  wholly  of  a  min- 
eral nature  it  should  be  mixed  with  some  pure  sugar,  about  half 
a  gram,  before  being  placed  in  the  tube.  When  bubbles  of  gas  no 
longer  come  over,  the  heat  should  be  carried  back  until  there  is 
a  gradual  evolution  of  carbon  dioxid  under  the  conditions  above 
noted.  Finally,  the  gas  is  turned  off  and  the  pump  kept  in  opera- 
tion until  the  manometer  again  shows  a  perfect  vacuum,  when 


CALCULATION    OF   RESULTS  331 

the  operation  may  be  considered  finished.  In  the  manipulation, 
our  chief  variation  from  the  official  method  consists  in  connect- 
ing the  combustion  apparatus  with  the  measuring  tube  before  the 
heat  is  applied  to  the  front  end  of  the  combustion  tube.  Any 
particles  of  the  sample  which  may  have  stuck  to  the  sides  of  the 
tube  on  filling,  will  thus  be  subject  to  combustion  and  the  gases 
produced  measured.  Where  it  is  certain  that  no  such  adhesion 
has  taken  place,  it  is  somewhat  safer  on  account  of  the  possible 
presence  of  occluded  gases  to  heat  the  front  end  of  the  tube  before 
connecting  the  combustion  apparatus  with  the  azotometer. 

291.  Method  of  Johnson  and  Jenkins. — In     the     method     of 
Johnson   and  Jenkins   the   principal   variation   from   the  process 
described   consists   in    introducing   into   the   combustion   tube    a 
source  of  oxygen  whereby  any  difficultly  combustible  carbon  may 
be  easily  oxidized  and  all  the  nitrogen  be  more  certainly  set  free.84 
The  potassium  chlorate  used  for  this  purpose  is  placed  in  the 
posterior    part     of    the    tube,     which  is  bent  at  a  slight  angle 
to  receive  it.     The  sodium  bicarbonate  is  placed  in  the  anterior 
end  of  the  tube.     The  combustion  goes  on  as  already  described, 
and  at  its  close  the  potassium  chlorate  is  heated  to  evolve  the 
oxygen.     The   free  oxygen  is  absorbed  by  the  reduced  copper 
oxid,    or   consumed  by  the  unburned   carbon.     Any   excess   of 
oxygen  is  recognized  at  once  by  its  action  on  the  copper  spiral. 
As  soon  as  this  shows  signs  of  oxidation  the  evolution  of  the  gas 
is  stopped.     Care  must  be  taken  not  to  allow  the  oxygen  to  come 
off  so  rapidly  as  to  escape  entire  absorption  by  the  contents  of 
the  combustion  tube.     In  such  a  case  the  nitrogen  in  the  meas- 
uring tube  would  be  contaminated. 

It  is  rarely  necessary  in  fertilizer  analysis  to  have  need  of  more 
oxygen  than  is  contained  in  the  copper  oxid  powder  in  contact 
with  the  sample  during  the  progress  of  combustion. 

292.  Calculation  of  Results.— The  nitrogen  originally  present 
in   a   definite   weight   of   any    substance   having   been    obtained 
in  a  gaseous  form,  its  volume  is  read  directly  in  the  burette  in 
which  it  is  collected.     This  instrument  may  be  of  many  forms 
but  the  essential  feature  of  its  construction  is  that  it  should  be 

M  American  Chemical  Journal,  i88o-8r,  2  :  27. 


332  AGRICULTURAL,   ANALYSIS 

accurately  calibrated,  and  the  divisions  so  graduated  as  to  per- 
mit of  the  reading  of  the  volume  accurately  to  a  tenth  of  a  cubic 
centimeter.  For  this  purpose  it  is  best  that  the  internal  diame- 
ter of  the  measuring  tube  be  rather  small  so  that  at  least  each 
10  cubic  centimeters  occupies  a  space  10  centimeters  long. 
The  volume  occupied  by  any  gas  varies  directly  with  the  tem- 
perature and  inversely  with  the  pressure  to  which  it  is  subjected. 
The  quantity  of  aqueous  vapor  which  a  moist  gas  may  contain 
is  also  a  factor  to  be  considered.  Inasmuch  as  the  nitrogen  in 
the  above  process  of  analysis  is  collected  over  a  strong  solution 
of  potassium  hydroxid  capable  of  practically  keeping  the  gas  in 
a  dry  state,  the  tension  of  the  aqueous  vapor  may  be  neglected. 

293.  Reading  the  Barometer. — Nearly  all  of  the  barometers  in 
use  in  this  country  have  the  scale  divided  in  inches  and  the 
thermometers  thereunto  attached  are  graduated  in  Fahrenheit 
degrees.  This  is  especially  true  of  the  barometers  of  the  Weather 
Bureau,  which  are  the  most  reliable  and  most  easy  of  access  to 
analysts.  It  is  not  necessary  to  correct  the  reading  of  the 
barometer  for  altitude,  but  it  is  important  to  take  account  of  the 
temperature  at  the  time  of  observation.  There  is  not  space  here 
to  give  minute  directions  for  using  a  barometer.  Such  direc- 
tions have  been  prepared  by  the  Weather  Bureau  and  those 
desiring  it  can  get  copies  of  the  circular.85 

The  temperature  of  a  barometer  affects  its  accuracy  in  two 
ways :  First,  the  metal  scale  expands  and  contracts  with  chang- 
ing temperatures ;  Second,  the  mercury  expands  and  contracts 
also  at  a  much  greater  rate  than  the  scale.  If  a  barometer  tube 
holds  30  cubic  inches  of  mercury,  the  contents  will  be  one 
ounce  lighter  at  80°  F.  than  at  32°  F.  The  true  pressure  of  the 
air  is,  therefore,  not  shown  by  the  observed  height  of  the  mercurial 
column,  unless  the  temperature  of  the  scale  and  of  the  mercurial 
column  be  considered. 

Tables  of  correction  for  temperature  are  computed  by  simple 
formulas  based  on  the  known  coefficients  of  expansion  of  mer- 

85  Barometers  and  the  Measurement  of  Atmospheric  Pressure,   2nd  Edi- 
tion, 1901. 


READING    THE    BAROMETER  333 

cury  and  brass.     For  barometers  with  brass  scales  the  following 
formula  is  used  for  making  the  correction : 
C  =  —  h  — '  ~  "8 ^     .     In  this  formula.  /  =    temperature    in 

1.113*   -t-  I0978  c 

degrees  Fahrenheit  and  /t— observed  reading  of  the  barometer 
in  inches. 

Example: — Temperature  observed  72°. 5 

Barometer  reading  observed,  29.415  inches, 

from  which  0=0.1165,  and  this  number,  according  to  the  con- 
ditions of  the  formula,  is  to  be  subtracted  from  the  observed 
reading.     The  true  reading  in  the  case  given  is,  therefore, 
29.298  inches  or  744-2  millimeters. 

The  observed  reading  747.1 
And  the  correction  2.9 

Unless  extremely  accurate  work  be  required,  the  correction  for 
temperature  is  of  very  little  importance  in  nitrogen  determina- 
tions in  fertilizers.  Each  instrument  sent  out  by  the  Weather 
Bureau  is  accompanied  by  a  special  card  of  corrections  therefor, 
but  these  are  of  small  importance  in  fertilizer  work.  In  order 
then  to  get  the  correct  weight  of  the  gas  from  its  volume,  the 
reading  of  the  thermometer  and  barometer  at  the  time  of  meas- 
urement must  be  carefully  noted.  However,  after  the  end  of  the 
combustion,  the  azotometer  should  be  carried  into  another 
room  which  has  not  been  affected  by  the  combustion  and  allowed 
to  stand  until  it  has  reached  the  room  temperature. 

Every  true  gas  changes  its  volume  under  varying  tempera- 
tures at  the  same  rate,  and  this  rate  is  the  coefficient  of  gaseous 
expansion.  For  one  degree  of  temperature  it  amounts  to  0.003665 
of  its  volume.  Representing  the  coefficient  of  expansion  by  K 
the  volume  of  the  gas  as  read  by  V,  the  volume  desired  at  any 
temperature  by  V,  the  temperature  at  which  the  volume  is  read 
by  t  and  the  desired  temperature  by  t',  the  change  in  volume 
may  be  calculated  by  the  following  formula: 
V'=V[i+K(*'-*)}. 

Example. — Let  the  volume  of  nitrogen  obtained  by  combus- 
tion be  35  cubic  centimeters,  and  the  temperature  of  observa- 
tion 22°.  What  would  be  the  volume  of  the  gas  at  o°  ? 


334  AGRICULTURAL   ANALYSIS 

Making  the  proper  substitutions  in  the  formula  the  equation 
is  reduced  to  the  form  below : 

V'=35  [  I  +0.003665  (0°-22°  )  ] 

or  V'= 35  (J— 0.08063)  =32.18. 

Thirty-five  cubic  centimeters  of  nitrogen,  therefore,  measured 
at  22°  becomes  32.18  cubic  centimeters  when  measured  at  o°. 

When  gases  are  to  be  converted  into  weight,  after  having  been 
determined  by  volume,  their  volume  at  o°  must  first  be  deter- 
mined; but  this  volume  must  also  be  calculated  to  some  definite 
barometric  pressure.  By  common  consent,  this  pressure  has  been 
taken  as  that  exerted  by  a  column  of  mercury  760  millimeters  in 
height.  Since  the  volume  of  a  gas  is  inversely  proportional  to 
the  pressure  to  which  it  is  subjected,  the  calculation  is  made 
according  to  that  simple  formula.  Let  the  reading  of  the  barom- 
eter, at  the  time  of  taking  the  volume  of  gas,  be  H,  and  any  other 
pressure  desired  H'.  Then  we  have  the  general  formula: 

HV 


V:V  =  H':H  :  and  V  = 


H' 


Example  :  Let  the  corrected  reading  of  the  barometer  at  the 
time  of  noting  the  volume  of  the  gas  be  740  millimeters,  and  the 
volume  of  the  gas  reduced  to  o°  be  32.18  cubic  centimeters. 
What  will  this  volume  be  at  a  pressure  of  760  millimeters  ? 

Substituting  the  proper  values  in  the  formula,  we  have: 

32.18  X  740 
V  ~  =31-33' 


Therefore,  a  volume  of  nitrogen  which  occupies  a  space  of 
35  cubic  centimeters  at  a  temperature  of  22°,  and  at  a  baro- 
metric pressure  of  740  millimeters,  becomes  31.33  cubic  centime- 
ters at  a  temperature  of  o°  and  a  pressure  of  760  millimeters. 

One  liter  of  nitrogen  at  o°  and  760  millimeters  pressure  weighs 
1.25456  grams;  and  one  cubic  centimeter,  therefore,  0.00125456 
gram.  To  find  the  weight  of  gas  obtained  in  the  above  supposed 
analysis,  it  will  only  be  necessary  to  multiply  this  number  by 
the  volume  of  nitrogen  expressed  in  cubic  centimeters  under  the 
standard  conditions;  viz.,  0.0125456X31.33=0.039305  gram. 


TENSION    OF    AQUEOUS    VAPOR 


335 


If  the  sample  taken  for  analysis  weighed  half  a  gram,  the  per- 
centage of  nitrogen  found  would  be  7.85. 

294.  Tension  of  the  Aqueous  Vapor. — It  has  been  shown  by 
experience  that  when  a  gas  is  collected  over  a  potash  solution 
containing  50  per  cent,  of  potassium  hydroxid,  the  tension  of 
the  aqueous  vapor  is  so  far  diminished  as  to  be  of  no  perceptible 
influence  on  the  final  result.  To  correct  the  volume  of  a  gas 
for  this  slight  tension  would  involve  an  unnecessary  calculation 
for  practical  purposes.  If  a  gas  thus  collected  should  be  trans- 
ferred to  a  burette  over  mercury,  on  which  some  water  floats, 
then  the  correction  should  be  made. 

At  o°  the  tension  of  aqueous  vapor  will  support  a  column  of 
mercury  4.525  millimeters,  and  at  40°  one  54.969  millimeters 
high. 

The  following  table  gives  the  tension  of  aqueous  vapors  in  mil- 
limeters of  a  mercurial  column  for  each  degree  of  temperature 
from  zero  to  40. 


Tension  of  vapor 

Tension  of  vapor 

Temperature. 

in  millimeters. 

Temperature. 

in  millimeters. 

0° 

4.525 

21° 

18.505 

1° 

4.867 

22° 

I9-675 

2° 

5.23I 

23° 

20.909 

3° 

5.6I9 

24° 

22.211 

4° 

6.032 

25° 

23.582 

5° 

6.471 

26° 

25.026 

6° 

6-939 

27° 

26.547 

7° 

7-436 

28° 

28.148 

8° 

7.964 

29° 

29.832 

9° 

8.525 

30° 

31.602 

10°       • 

9.126 

31° 

33.464 

11° 

9-751 

32° 

35.419 

12° 

10.421 

33° 

37-473 

13° 

11.130 

34° 

39-630 

14° 

11.882 

35° 

41-893 

15° 

12.677 

36° 

44.268 

16° 

13.519 

37° 

46.758 

17° 

14.409 

38° 

49.368 

18° 

I5.35I 

39° 

52.103 

19° 

16.345 

40° 

54.969 

20° 

I7-396 

When  a  gas  is  in  contact  with  water  the  aqueous  vapor  is  dif- 
fused throughout  the  mass,  and  the  pressure  to  which  the  mix- 


336 


AGRICULTURAL   ANALYSIS 


ture  is  subjected,  is  partly  neutralized  by  the  tension  of  the  water « 
vapor.  The  real  pressure  to  which  the  gas,  whose  volume  is  to 
be  determined,  is  subjected  is,  therefore,  diminished  by  that  ten- 
sion. If,  for  instance,  a  gas  in  contact  with  water  show  a  vol- 
ume of  35  cubic  centimeters  at  22°  and  740  millimeters  baromet- 
ric pressure,  its  volume  is  really  greater  than  if  it  were  perfectly 
dry.  How  much  greater  can  be  determined  by  inspecting  the 
table;  for  at  22°  the  tension  of  water  vapor  is  19.675  millime- 
ters of  mercury.  The  real  pressure  to  which  the  volume  of  gas 
is  subjected  is,  therefore,  740 — 19.675=720.325  millimeters. 

If,  therefore,  in  the  example  given,  the  nitrogen  were  in  con- 
tact with  water,  the  calculation  would  proceed  as  follows: 
32-18  X72Q.325  _ 


V  = 
And  30.5X1.25456=38-26. 


760 


Millimeters  tension  of  aqueous  vapor  for  KOH  solutions  of 


Tempera- 
ture. 

9.09  per 
cent. 

16.66  per 
cent. 

23.08  per 
cent. 

28.57  per 
cent. 

32.89  per 
cent. 

IO°.00 

8.62 

8.01 

7-31 

6.50 

5-62 

11°.  00 

9.21 

8.56 

7.82 

6-95 

6.01 

12°.  10 

9.90 

9.21 

8.41 

7-47 

6.46 

I3°.oo 

10.50 

9-77 

8.92 

7-93 

6.86 

I3°-95 

11.17 

10.39 

9-49 

8.44 

7.30 

15°.  15 

12.06 

11.22 

10.25 

9.11 

7.86 

i6°.oo 

12.74 

11.85 

10.82 

9.62 

8-33 

I7°.oo 

13-57 

12.63 

"•54 

10.26 

8.88 

i8°.oo 

14.46 

13-45 

12.29 

10.93 

9-47 

19°.  oo 

15.39 

14-33 

13.09 

11.65 

10.09 

20°.  oo 

16.38 

15.25 

13-93 

12.40 

10.75 

2I°.00 

17.42 

16.22 

14.82 

13.20 

11.44 

2I°.82 

18.32 

I7.06 

15-59 

13-88 

12.04 

23°.00 

19.68 

18.32 

16.75 

14.92 

12.94 

24°.00 

20.92 

19-47 

17.80 

15-86 

13-76 

25°.  oo 

22.19 

20.67 

18.91 

16.85 

14.62 

26°.  oo 

23-55 

21.94 

20.07 

17.89 

15-53 

26°.98 

24-95 

23.25 

21.27 

18.96 

16.46 

27°-93 

26.38 

24-59 

22.51 

20.07 

17-45 

29°.00 

28.08 

26.18 

23.96 

21.38 

18.59 

30°.  oo 

29.76 

27.74 

25.40 

22.67 

19.72 

3i°.oo 

31-51 

29.38 

26.91 

24.03 

20.91 

32°-  13 

33-61 

31-34 

28.72 

25-65 

22.34 

33°-oo 

35.30 

32.93 

30.18 

26.97 

23-50 

34°  .00 

37-34 

34.84 

31-94 

28.56 

24.89 

TABLES  FOR  CALCULATING  RESULTS  337 

Hence,  38.26  milligrams  of  nitrogen  correspond  to  7.65  per 
cent.,  when  half  a  gram  of  substance  is  taken  for  the  combustion. 

295.  Aqueous  Tension  in  Solutions  of   Potassium  Hydroxid.— 
Even  in  strong  solutions  of  potassium  hydroxid  the  tension  of 
aqueous  vapor  is  not  destroyed,  but  is  reduced  to  a  minimum, 
which  is  negligible  in  the  calculation  of  the  percentage  by  weight 
of  the  nitrogen  in  a  sample  of  fertilizer.     When  dilute  solutions 
of  a  caustic  alkali  are  used,  however,  the  neglect  of  the  tension  of 
the  aqueous  vapor  may  cause  an  error  of  some  magnitude.     In 
such  cases  the  strength  of  the  solution  should  be  known  and  cor- 
rection made  according  to  the  preceding  table.86 

296.  Use   of   Volumetric   Method. — For   practical  purposes     it 
may  be  said,  that  the  volumetric  determination  of  nitrogen  in 
fertilizer  analysis  has  gone  entirely  out  of  use.     For  control  and 
comparison  it  is  still  occasionally  practiced,  but  it  has  had  to  give 
way  to  the  more  speedy  and  fully  as  accurate  processes  of  moist 
combustion  with  sulfuric  acid,  which  have  come  into  general  use 
in  the  last  two  decades.     The  student  and  analyst,  however,  should 
not  fail  to  master  its  details  and  become  skilled  in  its  use.     There 
are  certain  nitrogenous  substances,  such  as  the  alkaloids,  which  are 
quite   refractory   when   subjected   to   moist   combustion.     While 
such  bodies  may  not  occur  in  fertilizers,  except  in  rare  cases 
such  as  nicotine  in  tobacco  waste,  it  is  well  to  have  at  hand 
a  means  of  accurately  determining  their  nitrogen  content. 

297.  Tables   for  Calculating   Results. — Where     many     analy- 
ses are  to  be  made  by  the  copper  oxid  process,  it  has  proved  con- 
venient to  shorten  the  work  of  calculating  analyses  by  taking 
the    data    given    in   computation   tables.87     Before    using   these 
tables  it  must  be  known  whether  they  are  calculated  on  the  sup- 
position that  the  gas  is  measured  in  a  moist  state,  partly  moist,  or 
wholly  dry.     Where  the  nitrogen  is  collected  over  water,  a  table 
must  be  used  in  which  allowance  has  been  made  for  the  tension 
of  aqueous  vapor.       In  case  a  saturated  solution  of  a  caustic 
alkali  be  used  in   the  azotometer,   it  is  customary  to  take   no 
account  of  the  tension  and  the  table  employed  must  be  con- 

M  Landolt  and  Bornstein,   Physikalisch-chetnische  Tabellen,  2nd  Edi- 
tion, 1894  :  68. 

87  Battle  and  Dancy,  Conversion  Tables,  1885  :  34. 


338  AGRICULTURAL   ANALYSIS 

strutted  on  this  supposition.  In  point  of  fact  even  in  the  strong- 
est alkali  solution  there  is  a  certain  amount  of  tension  but  this 
is  so  slight  as  only  to  affect  the  results  in  the  second  place  of 
decimals.  Since,  as  a  rule,  only  a  few  analyses  are  made  by  this 
method,  it  will  be  found  safer  to  use  a  caustic  alkali  solution  of 
given  strength  and  to  calculate  the  results  from  the  tables  of 
aqueous  tensions  given  above. 

298.  The  Soda-Lime  Process. — This  process  originally  per- 
fected by  Varrentrap  and  Will,  and  improved  by  Peligot,  was 
used  very  extensively  by  analysts  until  within  the  last  two  decades 
for  the  determination  of  nitrogen  not  existing  in  the  nitric  form. 
It  is  based  on  the  principle  that  when  nitrogen  exists  as  a  salt 
of  ammonia,  or  as  an  amid,  or  as  proteid  matter,  it  is  con- 
verted into  gaseous  ammonia  by  combustion  with  an  alkali. 
This  ammonia  can  be  carried  into  a  set  solution  of  acid  by  a  stream 
of  gas  free  of  ammonia  and  the  excess  of  acid  remaining  after 
the  combustion  is  complete  can  be  determined  by  titration  against 
a  standard  alkali  solution.  The  results  under  proper  conditions 
are  accurate  even  when  a  small  quantity  of  nitric  nitrogen  is 
present.  When,  however,  there  is  any  considerable  quantity  of 
this  compound  in  the  sample  the  method  becomes  inapplicable 
by  reason  of  non-reduction  of  some  of  the  nitrogen  oxids  pro- 
duced by  the  combustion. 

In  bodies  very  rich  in  nitrogen,  such  as  urea,  all  the  nitrogen 
is  not  transferred  directly  into  ammonia  at  the  commencement 
of  the  combustion.  A  portion  of  it  may  unite  with  a  part  of  the 
carbon  to  form  cyanogen,  which  may  unite  with  the  soda  to 
form  sodium  cyanid.  With  an  excess  of  alkali,  however,  and 
prolonged  combustion,  this  product  will  be  finally  decomposed 
and  all  the  nitrogen  be  secured  as  ammonia. 

The  nascent  hydrogen  which  unites  with  the  nascent  nitrogen 
during  the  combustion  is  also  derived  from  the  organic  matter 
which  always  contains  enough  carbon  to  decompose  the  water 
formed  in  order  to  be  oxidized  to  carbon  dioxid.  While  at  first, 
therefore,  during  combustion,  the  hydrogen  may  unite  with  the 
oxygen,  it  becomes  again  free  by  the  oxidation  of  the  carbon  and 
in  this  condition  unites  with  the  nascent  nitrogen  to  form  ammo- 


THE  OFFICIAL   METHOD  339 

nia.  In  addition  to  carbon  dioxid,  ammonia,  and  free  hydrogen 
there  may  also  be  found  among  the  products  of  combustion 
marsh  and  olefiant  gases  and  other  hydrocarbon  compounds 
which  dilute,  to  a  greater  or  less  extent,  the  ammonia  formed 
and  help  to  carry  it  out  of  the  combustion  tube  and  into  the 
standard  acid. 

299.  The  Official  Method. — Reagents  and  Apparatus. — (i) 
Standard  solutions  and  indicator  the  same  as  for  the  kjeldahl 
method. 

(2)  Dry  granulated  soda-lime,  fine  enough  to  pass  a  2.5  milli- 
meter sieve. 

(3)  Soda-lime,  fine  enough  to  pass  a  1.25  millimeter  sieve. 
Soda-lime  may  be  easily  and  cheaply  prepared  by  slaking  two 

and  one-half  parts  of  quicklime  with  a  strong  solution  of  one  part 
of  commercial  caustic  soda,  care  being  taken  that  there  is  enough 
water  in  the  solution  to  slake  the  lime.  The  mixture  is  then 
dried  and  heated  in  an  iron  pot  to  incipient  fusion,  and,  when 
cold,  ground  and  sifted  as  above. 

(4)  Sodium  Carbonate  and  Lime  or  Slaked  Lime. — Instead  of 
soda-lime  Johnson's  mixture  of  sodium  and  calcium  carbonate, 
or  slaked  lime,  may  be  used.     Slaked  lime  may  be  granulated-  by 
mixing  it  with  a  little  water  to  form  a  thick  mass,  which  is  dried 
in  the  water-oven  until  hard  and  brittle.     It  is  then  ground  and 
sifted  as  above.     Slaked  lime  is  much  easier  to  work  with  than 
soda-lime,  and  gives  excellent  results,  though  it  is  probable  that 
more  of  it  should  be  used  in  proportion  to  the  substance  to  be 
analyzed  than  is  the  case  with  soda-lime. 

(5)  Asbestos. — The  asbestos  used  should  be  ignited  and  kept  in 
a  glass-stoppered  bottle. 

(6)  Combustion  Tubes. — These  are  about  40  centimeters  long 
and  with  an  internal  diameter  of  12  millimeters,  drawn  out  to 
a  closed  point  at  one  end. 

(7)  U-Tubes.— Large-bulbed  U-tubes  with  glass  stop-cock,  or 
Will's  tubes  with  four  bulbs. 

Manipulation. — The  substance  to  be  analyzed  should  be  pow- 
dered finely  enough  to  pass  through  a  sieve  of  one  millimeter 
mesh ;  from  0.7  to  1.4  gram,  according  to  the  amount  of  nitrogen 


34O  AGRICULTURAL,  ANALYSIS 

present,  is  used  for  the  determination.  Into  the  closed  end  of 
the  combustion  tube  put  a  small  loose  plug  of  asbestos,  and  upon 
it  to  the  depth  of  about  four  centimeters,  fine  soda-lime.  In  a 
porcelain  dish  or  mortar  mix  the  substance  to  be  analyzed,  thor- 
oughly but  quickly,  with  enough  fine  soda-lime  to  fill  approxi- 
mately 1 6  centimeters  of  the  tube,  or  about  40  times  as  much  soda- 
lime  as  substance,  and  put  the  mixture  into  the  combustion  tube 
a£  quickly  as  possible  by  means  of  a  wide-necked  funnel,  rinsing 
out  the  dish  and  funnel  with  a  little  more  fine  soda-lime,  which 
is  to  be  put  in  on  top  of  the  mixture.  Fill  the  rest  of  the  tube  to 
within  about  five  centimeters  of  the  end  with  granulated  soda- 
lime,  making  it  as  compact  as  possible  by  tapping  the  tube  gently 
while  held  in  a  nearly  upright  position  during  the  filling.  The 
layer  of  granulated  soda-lime  should  not  be  less  than  12  centi- 
meters deep.  Lastly,  put  in  a  plug  of  asbestos  about  two  centi- 
meters long,  pressed  rather  tightly,  and  wipe  out  the  end  of  the 
tube  to  free  it  from  adhering  particles. 

Connect  the  tube  by  means  of  a  well-fitting  rubber  stopper  or 
cork  with  the  U-tube  or  Will's  bulbs,  containing  10  cubic  centi- 
meters of  standard  acid,  and  adjust  it  in  the  combustion  furnace 
so  that  the  end  of  the  tube  projects  about  four  centimeters  from 
the  furnace  suitably  supporting  the  U-tube  or  Will's  bulb.  Heat 
the  portion  of  the  tube  containing  the  granulated  soda-lime  to  a 
moderate  redness,  and  when  this  is  attained  extend  the  heat  grad- 
ually through  the  portion  containing  the  substance,  so  as  to  keep 
up  a  moderate  and  regular  flow  of  gases  through  the  bulbs,  main- 
taining the  heat  of  the  first  part  until  the  whole  tube  is  heated 
uniformly  to  the  same  degree.  Continue  the  combustion  until 
gases  have  ceased  bubbling  through  the  acid  in  the  bulbs,  and 
the  mixture  of  substance  and  soda-lime  has  become  white,  or 
nearly  so,  which  shows  that  the  combustion  is  finished.  The 
combustion  should  occupy  about  three-quarters  of  an  hour,  or  not 
more  than  one  hour.  Extinguish  the  burners  and  when  the  tube 
has  cooled  below  redness  break  off  the  closed  tip  and  aspirate  air 
slowly  through  the  apparatus  for  two  or  three  minutes  to  bring 
all  the  ammonia  into  the  acid.  Disconnect  the  tube,  wash  the 
acid  into  a  beaker  or  flask,  and  titrate  with  the  standard  alkali. 


THE  HYDROGEN  METHOD  34! 

During  the  combustion  the  end  of  the  tube  projecting  from 
the  furnace  must  be  kept  heated  sufficiently  to  prevent  the  con- 
densation of  moisture,  yet  not  enough  to  char  the  stopper.  The 
heat  may  be  regulated  by  a  shield  of  tin  slipped  over  the  pro- 
jecting end  of  the  combustion  tube. 

It  is  found  very  advantageous  to  attach  a  bunsen  valve  to  the 
exit  tube,  allowing  the  evolved  gases  to  pass  out  freely,  but  pre- 
venting a  violent  sucking  back  in  case  of  a  sudden  condensation 
of  steam  in  the  bulbs. 

300.  The  Official  French.  Method. — The  French  chemists  pre- 
fer to  drive  out  the  traces  of  ammonia  remaining  in  the  com- 
bustion tube  by  means  of  the  gases  arising  from  the  decomposi- 
tion  of   oxalic   acid.88     The  operation   is   conducted   by   mixing 
about  one  gram  of  oxalic  acid  with  enough  of  dry  granular  soda- 
lime  to  form  a  layer  of  four  centimeters  in  length  at  the  bottom 
of  the  tube.     The  rest  of  the  tube  is  then  charged  substantially 
as  directed  above.     At  the  end  of  the  combustion,  the  oxalic  ax:id 
is  decomposed  by  heat,  furnishing  sufficient  hydrogen  to  remove 
from  the  tube  all  traces  of  ammonia  which  it  may  contain.     The 
French  chemists  employ   for  titration,   either  normal  acids  and 
alkalies  or  some  decimal  thereof,  or  else  an  acid  of  such  strength 
as  to  have  each  cubic  centimeter  thereof  correspond  to  10  milli- 
grams of  nitrogen,  thus  making  the  computation  of  results  ex- 
ceedingly simple.     Such  an  acid  is  secured  when  one  liter  thereof 
contains  35  grams  of  pure  monohydric  sulfuric  acid  or  45  grams 
of  pure  crystallized  oxalic  acid.    The  corresponding  alkaline  re- 
agent should  contain,  in  each  liter,  40  grams  of  pure  potassium 
hydroxid. 

301.  The  Hydrogen  Method. — Thibault    and    Wagner    recom- 
mend that  the  combustion  with  soda-lime  be  conducted  in  an  at- 
mosphere   of   hydrogen ;   and   Loges    replaces   this   by   common 
illuminating  gas  freed  from  ammonia  by  conducting  it  through 
a    tube    filled    with   glass    balls    moistened   with    dilute    sulfuric 
acid89-90. 

In  these  cases  the  combustion  tube  is  left  open  at  both  ends 

88  Grandeau,   Trait£  d' Analyse    des    Matieres  agricoles,  3me  Edition, 
1897,  1  :  427. 

89  Zeitschrift  fur  analytische  Chemie,  1884,  23  :  557. 

90  Chemiker-Zeitung,  1884,  8  :  649,  1741. 


343  AGRICULTURAL  ANALYSIS 

and  the  materials  under  the  tube  confined  to  the  proper  posi- 
tion by  asbestos  plugs.  The  gases  used  act  in  a  merely  mechan- 
ical manner  and  their  use  affords  so  few  advantages  over  the 
method  of  aspirating  air  at  the  end  of  the  combustion  as  to  ren- 
der it  unadvisable. 

302.  Coloration  of  the  Product. — It  often  happens,  especially 
in  the  combustion  of  animal  products,  such  as  tankage  and  fish 
scrap,  that  the  acid  receiving  the  ammonia  is  deeply  colored  by 
the  condensation  of  some  of  the  other  products  of  combustion. 
This  coloration  interferes,  in  a  very  serious  way,  with  the  delicacy 
of  the  indicator  used  to  determine  the  end  of  the  reaction.     In 
this  case  the  liquid  may  be  mixed  with  an  alkali  and  distilled,  and 
the  ammonia  secured  in  a  fresh  portion  of  the  standard  acid  as 
in  the  moist  combustion  process  to  be  hereafter  described. 

303.  General  Considerations. — (i)  Preparation  of  the  Sample. 
— In  the  soda-lime  method  it  is  of  great  importance  that  the 
organic  substances  be  in  a  fine  state  of  subdivision  so  as  to  ad- 
mit of  intimate  mixture  with  the  alkali.     In  cases  where  frag- 
ments of  hoof,  horn,  hair,  or  similar  substances  are  to  be  pre- 
pared for  combustion,  it  is  advisable  to  first  decompose  them  by 
heating  with  a  small  quantity  of  sulfuric  acid.     The  excess  of 
acid  may  be  neutralized  with  marble  dust  and  the  resulting  mix- 
ture dried,  rubbed  to  a  fine  powder,  and  mixed  with  the  soda- 
lime  in  the  usual  way.     Care  must  be  taken  not  to  lose  any  of 
the  ammonia  from  the  sulfate,  which  may  possibly  be  formed  in 
mixing  with  the  soda-lime  in  filling  the  tube. 

(2)  Purity  of  Soda-Lime. — The  soda-lime  employed  must  be 
entirely  free  of  nitrogenous  compounds,  and  blank  combustions 
should  be  made  to  establish  its  purity  or  to  determine  the  mag- 
nitude of  the  corrections  to  be  made. 

(3)  Temperature. — The  temperature  of  the  combustion  should 
not  be  allowed  to  exceed  low  redness.     At  very  high  tempera- 
tures there  would  be  danger  of  decomposing  the  ammonia. 

(4)  Aspiration  of  Air. — Before     aspiring  a  current     of     air 
through  the  tube  to  remove  the  last  traces  of  ammonia,  the  gas 
should  be  put  out  under  the  furnace  and  the  tube  be  allowed  to 


OFFICIAL  RUFFLE  METHOD  343 

cool  below  redness  to  avoid  any  danger  of  acting  on  the  nitrogen 
in  the  air. 

304.  The   Ruffle  Soda-Lime   Method. — Many     attempts     have 
been  made  to  adapt  the  soda-lime  method  to  the  determination  of 
nitric  nitrogen.  Of  these,  the  process  devised  by  Ruffle  is  the  only 
one  which  has  proved  successful.91     The  method  is  founded  on 
the  action  of  sulfurous  vapors  on  the  nitrogen  oxids  produced  dur- 
ing the   combustion,  whereby  sulfuric  acid  is   formed  and  the 
nascent  nitrogen  is  joined  with  hydrogen  to  form  ammonia.     By 
this  process  all  the  nitrogen  contained  in  the  sample,  even  if  in 
the  nitric  form,  is  finally  obtained  as  ammonia.     In  the  original 
method  the  reagents  employed  were  sodium  thiosulfate,   soda- 
lime,  charcoal,  sulfur,  and  granulated  soda-lime.     Subsequently, 
the  official  chemists  substituted  sugar  for  the  charcoal.92     The 
method  was  used  for  a  long  time  by  the  official  chemists  and 
came   into   general    favor   until    displaced    by   the    simpler   and 
cheaper  processes  of  the  moist  combustion  method  adapted  to 
nitric  nitrogen.    As  finally  modified  and  used  by  the  official  chem- 
ists, the  process  is  conducted  as  described  below.93 

305.  The   Official   Ruffle   Method. — Reagents  and   Apparatus. 
—  (i)  The  standard  solutions  and  indicator  are  the  same  as  in 
the  kjeldahl  method. 

(2)  A  mixture  of  equal  parts  by  weight  of  fine-slaked  lime 
and  finely  powdered  sodium  thiosulfate  dried  at  100°. 

(3)  A  mixture  of  equal  parts  by  weight  of  finely  powdered 
granulated  sugar  and  flowers  of  sulfur. 

(4)  Granulated  soda-lime,  as  described  under  the  soda-lime 
method. 

(5)  Combustion  tubes  of  hard  Bohemian  glass  70  centimeters 
long  and  1.3  centimeters  in  diameter. 

(6)  Bulbed  U-tubes  or  Will's  bulbs,  as  described  under  the 
soda-lime  method. 

Manipulation. —  (a)     Clean  the  U-tube  and  introduce  10  cubic 
centimeters  of  standard  acid. 

(b)  Fill  the  tube  as  follows:    (i)  A  loosely  fitting  plug  of  as- 

91  Journal  of  the  Chemical  Society,  1881,  39  :  87. 

K  Division  of  Chemistry,  Bulletin  16,  1887  :  51. 

98  Division  of  Chemistry,  Bulletin  46,  Revised  Edition,  1899  :  19. 


344  AGRICULTURAL   ANALYSIS 

bestos,  which  has  been  recently  ignited,  is  placed  in  the  end  of  the 
tube  to  be  attached  to  the  absorption  apparatus,  and  then  2.5 
to  3.5  centimeters  in  depth  of  the  thiosulfate  mixture  is  added. 
(2)  The  portion  of  the  substance  to  be  analyzed  is  intimately 
mixed  with  from  five  to  10  grams  of  the  sugar  and  sulfur  mix- 
ture. (3)  Pour  on  a  piece  of  glazed  paper  or  in  a  porcelain 
mortar  a  sufficient  quantity  of  thiosulfate  mixture  to  fill  a  depth  of 
about  25  centimeters  of  the  tube,  add  the  substance  to  be  analyzed, 
as  previously  prepared,  mix  carefully,  and  pour  into  the  tube, 
shake  down  the  contents  of  the  tube,  clean  the  paper  or  mortar 
with  a  small  quantity  of  the  thiosulfate  mixture  and  pour  into 
the  tube,  and  fill  up  with  soda-lime  to  within  five  centimeters  of 
the  end  of  the  tube.  (4)  Place  another  plug  of  ignited  asbestos 
at  the  end  of  the  tube  and  close  with  a  cork.  ( 5 )  Hold  the  tube 
in  a  horizontal  position  and  tap  on  the  table  until  there  is  a  gas- 
channel  along  the  top  of  the  tube.  (6)  Make  connection  with 
the  U-tube  containing  the  acid,  aspirate  and  see  that  the  apparatus 
is  tight. 

The  Combustion. — Place  the  prepared  combustion  tube  in  the 
furnace,  letting  the  ends  project,  so  as  not  to  burn  the  corks. 
Commence  by  heating  the  soda-lime  portion  until  it  is  brought 
to  a  full  red  heat.  Then  turn  on  slowly  jet  after  jet  toward  the 
outer  end  of  the  tube,  so  that  the  bubbles  come  off  at  the  rate  of 
two  or  three  a  second.  When  the  whole  tube  is  red  hot  and  the 
evolution  of  the  gas  has  ceased  and  the  liquid  in  the  U-tube 
begins  to  recede  toward  the  furnace,  attach  the  aspirator  to  the 
other  limb  of  the  U-tube,  break  off  the  end  of  the  tube,  and  draw 
a  current  of  air  through  for  a  few  minutes.  Detach  the  U-tube 
and  wash  the  contents  into  a  beaker  or  porcelain  dish ;  add  a 
few  drops  of  the  cochineal  solution,  and  titrate. 

306.  Observations. — In  our  experience  we  have  found  it 
much  more  satisfactory  to  adhere  to  the  earlier  directions  for 
preparing  the  mixture  of  thiosulfate  and  alkali.  We  much  pre- 
fer to  make  the  mixture  with  soda-lime  and  without  the  pre- 
vious drying  of  the  sodium  salt.  Ruffle  himself  says  that  the 
sodium  thiosulfate  should  be  dry,  but  not  deprived  of  its  water  of 


BOYER'5   MODIFICATION    OF  RUFFLE'S    METHOD  345 

crystallization.94  The  best  method  to  dry  the  salt  without  de- 
priving it  of  its  crystal  water  is  to  press  it  between  blotting  papers. 

As  is  seen  from  the  above  description  the  method  is  essen- 
tially a  reduction  process  by  the  action  of  a  powerful  deoxidizer 
in  the  presence  of  an  alkali.  The  crystals  of  the  thiosulfate  salt 
cannot  be  brought  into  direct  contact  with  a  pure  alkali,  like  soda 
or  potash,  without  forming  at  once  a  wet  mass  which  would  tend 
to  cake  and  obstruct  the  tube.  The  soda-lime  is,  therefore,  a  me- 
chanical device  to  prevent  this  fusion.  Where  many  analyses 
are  to  be  made,  an  iron  tube,  for  economical  reasons,  may  be  sub- 
stituted for  the  glass ;  but  the  glass  tube  permits  a  more  intelli- 
gent observation  of  the  progress  of  the  analysis. 

Since  charcoal  has  very  high  absorbent  powers  it  will  be  found 
always  to  contain  a  little  nitrogen  which  may  be  in  a  form  to 
generate  ammonia  during  the  combustion.  The  charcoal  used 
should,  therefore,  be  previously  boiled  with  caustic  soda  or  potash 
solution,  dried,  powdered,  and  preserved  in  well-stoppered  .bot- 
tles. Although  pure  sugar  is  practically  free  of  nitrogen,  even 
when  it  is  used,  it  is  advisable  to  occasionally  make  a  blank  deter- 
mination and  thus  ascertain  the  correction  to  be  made  for  possi- 
ble contamination. 

307.  Boyer's  Modification  of  Ruffle's  Method. — The  prin- 
ciple of  the  method  rests  on  the  observation  that  if  nitrates  be 
heated  in  a  combustion  tube  with  calcium  oxalate  and  soda-lime, 
not  more  than  two-thirds  of  the  total  nitrogen  appear  as  ammo- 
nia ;  but  if  a  certain  proportion  of  sulfur  be  added  the  whole  of 
the  nitrogen  is  recovered.95  The  process  may  be  divided  into 
two  steps ;  viz. : 

(1)  Action  of  the  calcium  oxalate  upon  the  sodium  nitrate  in 
presence  of  soda-lime. 

(2)  The  action  of  sulfurous  acid  and  of  calcium  oxalate  upon 
the  sodium  nitrate  in  presence  of  soda-lime. 

The  analysis  is  conducted  as  follows :  Dry  and  pulverize  one- 
half  gram  of  nitrate  and  mix  it  intimately  with  50  grams  of  the 
reducing  compound  containing  approximately  10  per  cent,  sulfur, 

M  Journal  of  the  Society  of  Chemical  Industry,  1883,  2  :  21. 

95  Comptes  rendus,  1891,  113  :  503. 


346  AGRICULTURAL  ANALYSIS 

22.5  per  cent,  neutral  calcium  oxalate,  and  67.5  per  cent,  soda-lime. 
The  combustion  tube  has  a  length  of  55  centimeters  and  a  diame- 
ter of  17  millimeters,  and  is  charged  as  follows: 

Two  grams  pulverized  calcium  oxalate. 

Ten  grams  pulverized  soda-lime. 

Ten  grams  of  the  reducing  compound. 

The  nitrate  incorporated  with  50  grams  of  the  reducing  mix- 
ture: 

Ten  grams  of  the  reducing  mixture. 

Ten  grams  pulverized  soda-lime. 

The  tube  is  then  tightly  closed  with  an  asbestos  plug  and  heated 
gradually  from  the  front  backwards,  the  calcium  oxalate  fur- 
nishing finally  the  gas  necessary  to  drive  out  the  last  traces  of 
ammonia. 

The  combustion  should  be  terminated  in  40  minutes  and  when 
completed,  the  acid,  containing  the  ammonia,  is  placed  in  a  beaker 
and  .boiled  for  two  or  three  minutes  to  drive  off  the  sulfurous 
and  carbonic  acids.  The  titration  is  then  conducted  in  the  usual 
manner. 

The  combustion  can  be  carried  on  just  as  well  in  an  iron  tube 
as  in  a  glass  one.  The  reagents  employed,  especially  soda-lime, 
being  hygroscopic,  a  little  water  is  disengaged  in  heating,  which 
is  condensed  at  the  cold  extremity  of  the  tube,  and  which  may 
absorb  a  little  ammonia  unless  special  precautions  are  taken  to 
have  the  materials  dry. 

The  process  is  equally  applicable  to  the  determination  of  nitro- 
gen in  all  its  forms  or  to  mixtures  thereof.  The  method  has  also 
been  applied  to  the  mixture  of  ammoniacal  and  organic  nitrogen 
and  to  the  mixture  of  ammoniacal,  nitric,  and  organic  nitrogen, 
the  combustions  having  been  made  both  in  an  iron  and  a  glass 
tube.  The  amounts  of  material  to  be  used  vary  from  one-half 
gram  to  a  gram,  according  to  its  richness  in  nitrogen. 

THE  MOIST  COMBUSTION  PROCESS 

308.  Historical. — As  long  ago  as  1868  Wanklyn  proposed  to 
conduct  the  combustion  of  organic  bodies  in  a  wet  way,  using 
potassium  permanganate  as  the  oxidizing  body.98  About  10  years 
96  Journal  of  the  Chemical  Society,  1868,  21  :  161. 


METHOD    OF    KJELDAHL  347 

after  this  he  attempted  to  extend  the  method  so  as  to  estimate 
the  quantity  of  proteid  matter  in  a  sample  by  treatment  with  an 
alkaline  solution  in  presence  of  the  permanganate  salt.  One  gram 
of  the  finely  pulverized  sample  was  treated  in  a  liter  flask  with 
one-tenth  normal  potash  lye.  According  to  the  supposition  of 
Wanklyn,  pure  albuminoid  matters  thus  treated  yielded  o.i  of 
their  weight  of  ammonia,  or  about  50  per  cent,  of  the  total  nitro- 
gen appeared  as  ammonia.  The  ammonia  content  of  the  sample 
was  determined  by  the  colorimetric  process  devised  by  Nessler. 
It  is  needless  to  add  that  the  process  of  Wanklyn  proved  to  be 
of  no  practical  use  whatever,  acting  differently  on  different  al- 
buminoid matters,  and  even  on  the  same  substance.  No  other 
attempt  was  made  to  perfect  the  moist  combustion  process  until 
Kjeldahl  introduced  the  sulfuric  acid  method  in  1883.  The  sim- 
plicity, economy,  and  adaptability  of  this  method  have  brought  it 
into  general  use.  At  first  the  process  was  only  applied  to  organic 
nitrogenous  compounds  in  the  absence  of  nitrates,  but  especially 
by  the  modifications  proposed  by  Asboth,  Jodlbauer,  and  Scovell 
it  has  been  made  applicable  to  all  cases,  with  the  possible  exception 
of  a  few  alkaloidal  and  allied  bodies.  The  moist  combustion  pro- 
cess for  determining  nitrogen  is  now  generally  employed  by 
chemists  in  all  countries,  not  only  for  fertilizer  control,  but  also 
for  general  work. 

309.  The  Method  of  Kjeldahl. — The  process  originally  pro- 
posed by  Kjeldahl  is  applicable  only  to  nitrogenous  bodies  free 
of  nitric  nitrogen.  The  principle  of  the  process  is  based  on  the 
action  of  concentrated  sulfuric  acid  at  the  boiling-point  in  de- 
composing nitrogenous  compounds  without  producing  volatile 
combinations  and  the  subsequent  completion  of  the  oxidation  by 
means  of  potassium  permanganate.  The  original  process  has 
been  modified  by  many  analysts,  but  the  basic  principle  of  it  has 
remained  unchanged.  It  will,  therefore,  prove  useful  here  to 
describe  the  process  as  originally  given.97 

The  substance  is  placed  in  a  small  digestion  flask  of  resistant 
glass.  Liquids  which  are  not  decomposed  on  heating  are  evap- 
orated in  a  thin  glass  dish,  which  can  be  ground  up  and  placed 

»7  Zeitschrift  fur  analytische  Chemie,  1883,  22  :  366. 


AGRICULTURAL  ANALYSIS 

in  the  digestion  flask  with  the  desiccated  sample.  The  strongest 
sulfuric  acid  is  added  in  sufficient  quantity,  not  less  than  10  cubic 
centimeters  in  any  case,  to  secure  complete  decomposition.  The 
acid  must  be  free  of  ammonia  and  be  kept  in  such  a  way  as  not 
to  absorb  ammonia  from  the  atmosphere  of  the  laboratory.  To 
guard  against  danger  of  error  from  such  an  impurity,  frequent 
control  determinations  should  be  made.  In  control  experiments 
one  or  two  grams  of  pure  sugar  are  used  as  the  organic  matter. 
If  the  acid  employed  contain  traces  of  ammonia,  the  necessary 
corrections  should  be  made  in  each  analysis. 

The  flask  having  been  charged  is  placed  on  a  wire  gauze  over 
a  small  flame.  The  organic  matter  becomes  black  and  tar-like, 
and  soon  there  is  a  rapid  decomposition,  attended  with  the  evolu- 
tion of  gaseous  products,  among  which  sulfur  dioxid  is  found. 
To  avoid  danger  from  spurting,  the  digestion  flask  is  placed  in  an 
oblique  position.  The  flask  should  have  a  capacity  of  at  least 
loo  cubic  centimeters,  and  a  long  neck  and  be  made  of  a  kind  of 
glass  capable  of  withstanding  the  action  of  the  boiling  acid.  Par- 
ticles of  the  carbonized  organic  matter  left  on  the  sides  of  the 
flask  by  the  foaming  of  the  mass  at  first  are  gradually  dissolved 
by  the  vapors  of  the  boiling  acid  as  the  digestion  proceeds.  The 
action  of  the  sulfuric  acid  is  not  entirely  finished  when  gases 
cease  to  be  given  off,  but  the  digestion  should  be  continued  until 
the  liquid  in  the  flask  is  clear  and  colorless,  or  nearly  so.  Usually 
about  two  hours  are  required  to  secure  this  result.  When  aided 
by  the  means  mentioned  below,  the  time  of  digestion  can  be  very 
materially  shortened.  By  adding  some  fuming  sulfuric  acid,  or 
glacial  phosphoric  acid,  the  dilution  caused  by  the  formation  of 
water  in  the  combustion  of  the  organic  matter  can  be  avoided. 
For  albuminoid  bodies  it  is  hardly  necessary  to  continue  the 
combustion  until  all  carbonaceous  matter  is  destroyed.  The  full 
complement  of  ammonia  is  usually  obtained  after  an  hour's  com- 
bustion, even  if  the  liquid  be  still  black  or  brown,  but  with  other 
nitrogenous  bodies  the  case  is  different,  so  that  upon  the  whole 
it  is  safest  to  secure  complete  decoloration. 

The  temperature  must  be  maintained  at  the  boiling-point  of 


METHOD    OF    KJELDAHL  349 

the  acid  or  near  thereto,  since  at  a  lower  temperature,  for  instance, 
from  1 00°  to  150°,  the  formation  of  ammonia  is  incomplete. 
Since  all  organic  substances  of  whatever  kind  are  dissolved  by 
the  boiling  acid,  the  previous  pulverization  of  the  material  need 
be  carried  only  far  enough  to  secure  a  fair  sample.  Many  sub- 
stances give  up  practically  all  their  nitrogen  as  ammonium  sul- 
fate  when  heated  with  sulfuric  acid,  as,  for  instance,  urea,  as- 
paragin,  and  the  glutens.  In  most  of  the  other  organic  bodies 
fully  90  per  cent,  of  the  nitrogen  is  likewise  secured  as  the  am- 
monium salt.  In  the  aromatic  compounds,  or  even  in  the  form 
•of  amid  in  anilin  salts,  the  nitrogen  is  more  resistant  to  the  action 
of  sulfuric  acid.  In  the  alkaloids  where  the  nitrogen  is  probably 
a  real  component  of  the  benzol  skeleton,  the  formation  of  am- 
monia is  very  incomplete.  But  even  in  the  cases  where  the  con- 
version of  the  nitrogen  into  ammonia  is  practically  perfect,  it  is 
advisable  to  finish  the  process  by  completing  the  oxidation  with 
potassium  permanganate.  The  permanganate  should  be  used  in 
a  dry  powdered  form  and  added  little  by  little  to  the  hot  con- 
tents of  the  digestion  flask,  the  latter  being  held  in  an  upright 
position  and  removed  meanwhile  from  the  lamp.  When  carefully 
performed  there  is  no  danger  of  loss  of  ammonia,  although  the 
oxidation  is  at  times  so  vigorous  as  to  be  attended  with  evolu- 
tion of  light.  The  permanganate  must  always  be  added  in  excess 
and  until  a  permanent  green  color  is  produced.  The  flask  is 
.  then  gently  heated  for  from  five  to  10  minutes  over  a  small  flame, 
but  this  is  not  important.  The  heating  must  not  be  too  strong, 
or  else  a  strong  evolution  of  oxygen  will  take  place,  with  a  con- 
sequent reduction  of  the  manganese  compound.  When  this  hap- 
pens the  liquid  again  becomes  clear  and  there  is  a  loss  of  am- 
monia. 

After  cooling,  the  contents  of  the  flask  are  diluted  with  water, 
the  green  color  giving  place  to  a  brown,  with  a  rise  of  tempera- 
ture. After  cooling  a  second  time,  the  whole  is  brought  into  a 
distillation  flask  of  about  three-quarters  of  a  liter  capacity  and 
attached  to  a  condenser  which  ends  in  a  vessel  containing  titrated 
sulfuric  acid.  About  40  cubic  centimeters  of  sodium  hydroxid 
.solution  of  1.3  specific  gravity  are  added  and  the  stopper  at  once 


35°  AGRICULTURAL  ANALYSIS 

inserted  to  prevent  any  loss  of  ammonia.  To  prevent  bumping, 
some  zinc  dust  is  added,  securing  an  evolution  of  hydrogen  dur- 
ing the  progress  of  the  distillation.  In  this  case  the  bumping  is 
prevented  until  near  the  end  of  the  operation,  when  it  begins 
anew,  probably  by  reason  of  the  separation  of  solid  sodium 
sulfate.  After  the  end  of  the  distillation,  the  excess  of  acid  re- 
maining in  the  receiver  is  determined  by  a  set  alkali  solution, 
and  thus  the  quantity  of  ammonia  obtained  easily  calculated. 
Kjeldahl,  however,  preferred  to  titrate  the  solution  after  adding 
potassium  iodate  and  iodid,  a  mixture  which  in  the  presence  of 
a  strong  acid  sets  free  a  quantity  of  iodin  equivalent  to  the  free 
acid  present.  The  iodin  thus  set  free  is  titrated  by  a  set  solu- 
tion of  sodium  thiosulfate,  using  starch  as  an  indicator.  The 
merits  of  this  method  are  sharpness  of  the  end  reaction  and  the 
possibility  of  using  only  a  small-  quantity  of  the  nitrogenous  body 
for  the  combustion.  The  sulfuric  acid  used  in  the  receiver  is 
made  of  the  same  strength  as  the  thiosulfate  solution ;  viz.,  about 
one-twentieth  normal.  Thirty  cubic  centimeters  of  this  were 
found  to  be  the  proper  amount  for  use  with  substances  oxidized 
in  such  quantities  as  to  produce  ammonia  enough  to  neutralize 
about  half  of  it.  The  titration  is  carried  on  as  follows :  A  few 
crystals  of  potassium  iodid  are  dissolved  in  the  acid  mixture  ob- 
tained after  the  distillation  is  completed,  then  a  few  drops  of  the 
starch-paste,  and  finally  a  few  drops  of  a  four  per  cent,  solution 
of  potassium  iodate.  The  iodin  set  free  is  then  oxidized  by  the 
addition  of  the  one-twentieth  normal  sodium  thiosulfate  solution 
until  the  blue  color  disappears. 

Example:  Sulfuric  acid  used,  30  cc. 
Equivalent  to  sodium  thiosulfate,  30  cc. 
Blank  combustion  required,  29.8  cc.  thiosulfate  solution. 

Combustion  of  0.645  gram  of  bar- 
ley required,  •  14.5  cc. 
Thiosulfate  corresponding  to  bar- 
ley,                                               15.3  cc. 

In  the  computation  it  is  more  simple  to  multiply  the  corre- 
sponding number  of  cubic  centimeters  of  thiosulfate  by  seven, 
half  the  atomic  weight  of  nitrogen,  and  divide  the  product  by  the 


METHOD    OF    KJELDAHL  351 

weight  of  the  substance,  which  will  give  the  per  cent,  of  nitro- 
gen therein. 

Then      '       —    =    1.66  =  per  cent,  of  nitrogen  in  sample. 

"T  *  O 

A  more  detailed  description  of  the  method  of  making  the  titra- 
tion  follows:  After  the  distillation  is  finished  the  condensing- 
tube  is  rinsed  with  a  little  water,  after  which  the  sulfuric  acid 
nnneutralized  in  the  receiver  is  determined.  It  is  advisable  first 
to  test  the  reaction  of  the  distillate  with  litmus  paper  before  going 
any  further ;  for  if  at  any  time  all  the  acid  should  be  found  neu- 
tralized it  will  be  necessary  to  add  a  sufficient  quantity  of  one- 
twentieth  normal  sulfuric  acid  before  adding  the  potassium  iodid, 
etc.,  otherwise  the  determination  will  be  irreparably  lost.  Add 
to  the  contents  of  the  flask  10  cubic  centimeters  of  the  potassium 
iodid  and  two  cubic  centimeters  of  the  potassium  iodate  solutions, 
described  further  on,  and  the  sodium  thiosulfate  is  then  run  in 
from  a  burette  till  the  fluid,  which  is  constantly  kept  agitated  by 
shaking  the  flask,  shows  only  a  bare  trace  of  yellow  coloration 
from  the  iodin  still  present.  Starch  solution  is  then  added,  and 
the  blue  color  obtained  is  at  once  removed  by  additional  thio- 
sulfate solution.  When  some  experience  has  been  gained,  the 
•eve  is  able  to  discern,  with  great  certainty,  even  the  slight  color- 
ation caused  by  only  a  small  trace  of  free  iodin. 

In  regard  to  the  sensitiveness  of  the  end  reaction  and  the  ac- 
curacy of  the  result,  this  method  of  titration  leaves  nothing  to  be 
wished  for.  The  strength  of  the  thiosulfate  solution  is  deter- 
mined in  exactly  the  same  manner,  and  with  starch  as  an  indica- 
tor. For  this  purpose,  measure  10  cubic  centimeters  of  one- 
twentieth  normal  sulfuric  acid  into  an  erlenmeyer,  add  120  cubic 
centimeters  of  ammonia-free  water,  10  cubic  centimeters  of  potas- 
sium iodid  solution,  and  two  cubic  centimeters  of  iodate  solution ; 
add  thiosulfate  solution  till  the  fluid  shows  only  the  above  men- 
tioned light  yellow  tint,  then  add  starch,  and  finally  thiosulfate. 
In  this  way  the  strength  of  the  thiosulfate  is  ascertained,  which 
of  course,  must  be  occasionally  redetermined,  under  exactly  the 
same  conditions  as  obtain  in  the  nitrogen  determinations,  and 


t 
352  AGRICULTURAL   ANALYSIS 

every  possible  error  is  thereby  excluded.  That  the  solution  once 
decolorized  within  a  short  time  again  assumes  a  deep  blue  color, 
is  a  matter  of  no  concern,  inasmuch  as  both  solutions  are  added 
in  such  a  manner  that  the  end  reaction  lies  exactly  at  the  point 
when  the  starch  iodid  reaction  distinctly  disappears. 

310.  Theory  of  the  Reactions. — As  has  been  seen  above,  the 
final  product  of  heating  a  nitrogenous  organic  compound  with 
sulfuric  acid  and  an  oxidizing  body  is  ammonium  sulfate.     The 
various   steps  by   which  this   is   obtained   have  been   traced  by 
Dafert.98 

1 i )  The  sulfuric  acid  abstracts  from  the  organic  matter  the 
elements  of  water, 

(2)  The  sulfur  dioxid  produced  by  the  action  of  the  residual 
carbon  on  sulfuric  acid  exercises  a  reducing  effect  on  the  nitrog- 
enous bodies  present. 

(3)  From  the  nitrogenous  bodies  produced  by  the  above  re- 
duction ammonia  is  formed  by  the  action  of  an  oxidizing  body. 

(4)  The  ammonia  formed  is  at  once  fixed  by  the  acid  as  am- 
monium sulfate.    According  to  the  theory  of  Asboth,  the  hydro- 
gen which  is  formed  during  the  action  of  sulfuric  acid  on  organic 
matter,  when  in  a  nascent  state,  also  aids  greatly  in  the  produc- 
tion of  ammonia.     This  idea  is  based  on  the  fact  that  with  those 
bodies  which  afford  a  deficit  of  hydrogen  the  formation  of  am- 
monia is  imperfect." 

311.  Preparation  of  Reagents. — (i)  Pure  Sulfuric  Acid. — As 
is  well  known,  the  so-called  pure  sulfuric  acid  in  the  market 
usually  contains  ammonia,  a  fact  which  compelled  Kjeldahl  to 
determine  the  quantity  of  nitrogen  in  the  acid  in  every  instance, 
and  to  make  correction  for  the  same  in  the  analysis.     An  acid  • 
absolutely  free  from  this  impurity  may,  however,  readily  be  pre- 
pared by  the  distillation  of  the  commercial  article  in  a  small  glass 
retort  holding  easily  about  400  cubic  centimeters.     To  conduct 
this  operation  without  danger  it  is  only  necessary  to  arrange  the 
apparatus  so  that  the  heavy  fluid  is  heated  to  boiling,  not  from 
the  bottom  of  the  retort,  but  from  its  sides,  and  that  the  upper 

98  Zeitschrift  fiir  analytische  Chemie,  1885,  24  :  455- 
w  Chemisches  Central-Blatt,  1886  :  165. 


PREPARATION  OF  REAGENTS  353 

portion  of  the  body  and  neck  is  kept  sufficiently  warm  to  prevent 
the  sulfuric  acid  fumes  from  condensing  and  flowing  back  into 
the  retort.  Both  these  ends  are  attained  by  surrounding  the  re- 
tort with  a  piece  of  sheet  iron,  cylinder-shaped  beneath,  and  with 
an  oval  upper  part,  having  an  opening  of  about  one  centimeter 
in  diameter  for  the  neck  of  the  retort.  To  conduct  the  distilla- 
tion, a  burner  is  used  with  an  arrangement  for  spreading  the 
flame.  To  avoid  with  certainty  all  bumping  of  the  sulfuric  acid 
and  the  resulting  danger  therefrom,  the  lamp  is  so  arranged  that 
only  the  products  of  combustion  go  up  between  the  retort  and 
its  iron  hood,  without  allowing  the  flame  itself  to  come  into  con- 
tact with  the  glass  vessel.  The  retort  should  be  filled  about  half 
full,  or  with  200  cubic  centimeters  of  acid.  By  this  device,  with- 
out any  danger  whatever,  about  one  liter  of  sulfuric  acid  may 
be  distilled  in  a  day.  The  retort  will  stand  numerous  distilla- 
tions. Once  begun,  the  distillation  takes  care  of  itself ;  it  is  neces- 
sary to  discontinue  it  when  only  the  bottom  of  the  retort  is  cov- 
ered with  sulfuric  acid,  and  to  fill  with  fresh  acid  through  a  funnel 
when  the  retort  has  cooled  off.  The  first  20  cubic  centimeters 
of  the  distillate  going  over  are  collected  by  themselves  and  re- 
jected. What  comes  over  later  is,  as  shown  by  experience,  ab- 
solutely ammonia-free,  and  can  be  used  without  any  correction 
for  the  nitrogen  determinations  according  to  Kjeldahl.  The  acid 
is  kept  in  a  stoppered  bottle  in  a  place  not  reached  by  ammonia 
fumes.  The  10  cubic  centimeter  pipette  used  for  measuring  the 
quantity  of  sulfuric  acid  required  for  each  determination  is  fast- 
ened in  the  perforated  rubber  stopper  with  which  the  bottle  is 
kept  closed,  and  is  itself  closed  above  by  a  small  rubber  tube 
with  a  plug  of  glass  wool  in  it. 

(2)  Potassium  Permanganate. — Crystals  of  this  salt  are  crushed 
(not  pulverized)   with  a  pestle  into  small  pieces  of  about  one- 
half  millimeter  size,  which  are  kept  in  a  long  glass  tube  of  about 
ten  millimeters  diameter,  closed  with  a  stopper. 

(3)  Ammonia-free  Water. — Common  distilled  water  can  not  be 
used  in  the  determination  of  nitrogen  according  to  Kjeldahl,  since 
it  contains  ammonia.   Water  may  be  obtained  free  from  ammonia 

12 


354  AGRICULTURAL   ANALYSIS 

by  redistillation  in  a  large  glass  retort  with  the  addition  of  a  few 
drops  of  sulfuric  acid.  All  vessels  used  in  the  determination 
are  rinsed  out  beforehand  with  this  water. 

(4)  Ammonia-free  Soda-lye  is  most  conveniently  prepared  by 
adding  270  grams  of  common  sodium  hydroxid  in  sticks,  little 
by  little,  to  one  liter  of  distilled  water  which  is  kept  continually 
boiling,  by  means  of  a  small  flame,  in  a  good-sized  silver  dish. 
The  dish  is  kept  covered  with  a  glass  plate.    Care  has  to  be  exer- 
cised not  to  add  the  alkali  too  rapidly,  nor  in  too  large  quantities 
at  a  time,  for  in  this  case  the  fluid  will  boil  too  violently  at  every 
addition  of  the  alkali.     After  the  operation  is  finished  the  lye  is 
at  once  siphoned  into  a  glass  flask,  and  when  cold  is  poured  into 
a  glass-stoppered  bottle. 

(5)  One-twentieth  Normal  Sulfuric  Acid  is  prepared  from  sul- 
furic acid  and  water,  both  absolutely  ammonia-free,  and  is  kept 
ii)  a  place  where  no  fumes  of  ammonia  can  reach  it,  in  a  well- 
stoppered  glass  bottle,  the  stopper  being  smeared  with  vaseline. 

(6)  Sodium  Thiosulfate  Solution. — This  should  be  of  the  same 
strength  as  the  one-twentieth  normal  sulfuric  acid.     It  is  pre- 
pared by  dissolving  the  salt  in  ammonia-free  water  and  is  com- 
pared with  the  acid,  to  which  has  been  added  potassium  iodid 
and  iodate,  using  starch  as  an  indicator,  in  the  manner  described 
above.     The  solution  is  kept  in  a  well-stoppered  bottle,  in  the 
dark.     When  the  salt  and  water  used  are  perfectly  pure,  it  will 
keep  unchanged  for  a  long  time. 

(7)  Potassium  Iodid. — Dissolve  five  grams  of  chemically  pure 
potassium  iodid  in  ammonia-free  water  and  make  the  volume  100 
cubic  centimeters.     Keep  the  solution  in  the  dark  and  in  a  well- 
stoppered  bottle.     Ten  cubic  centimeters  bf  this  solution  are  used 
for  each  determination. 

(8)  Potassium  Iodate. — Dissolve  four  grams  of  chemically  pure 
potassium  iodate  in  ammonia-free  water  and  make  the  volume 
100  cubic  centimeters.     Use  two  cubic  centimeters  of  this  solu- 
tion for  each  determination. 

(9)  Starch  Solution. — Digest  pure  starch   for  about  a  week 
with  dilute  hydrochloric  acid,  wash  perfectly  free  from  chlorin 


MODIFICATIONS  OF  THE  KJELDAHL  PROCESS  355 

by  decantation,  and  finally  dry  it  between  filter-paper.  The  starch 
is  then  suspended  in  water  with  the  aid  of  heat.  Such  a  solu- 
tion will  keep  for  an  indefinite  time  if  it  be  saturated  with  com- 
mon salt.  Ten  grams  of  this  starch  are  dissolved  in  1,000  cubic 
centimeters  of  ammonia-free  water  and  one  or  two  cubic  centi- 
meters used  for  each  determination. 

312.  Modifications  of  the  Kjeldahl  Process. — It  would  be  im- 
practicable here  to  give  even  a  summary  of  the  many  unimportant 
changes  which  the  moist  combustion  process  has  undergone  since 
the  first  papers  of  its  author  were  published.  These  changes  may 
be  divided  into  three  classes ;  viz. : 

i.  Those  changes  which  refer  solely  to  the  quantities  of  sub- 
stance used  for  analysis,  to  the  composition  of  the  acid  mixture, 
to  the  duration  of  the  digestion,  to  the  form  and  size  of  the  flasks, 
both  for  digestion  and  distillation,  and  to  the  manner  of  distilla- 
tion and  of  titration.  For  references  to  the  papers  on  these  sub- 
jects the  reader  may  consult  Fresenius.1  The  most  important 
of  these  minor  changes  are  the  following:  Instead  of  the  titra- 
tion by  means  of  separated  iodin  most  chemists  have  had  recourse 
to  the  simpler  method  of  direct  titration  of  the  excess  of  acid  by  a 
set  solution  of  an  alkali.  Ammonium,  barium,  sodium,  and  potas- 
sium hydroxids  are  the  alkaline  solutions  most  employed.  This 
process  permits  of  a  larger  quantity  of  the  sample  being  taken  for 
combustion  and  of  the  use  of  a  larger  quantity  of  acid  in  the  re- 
ceiver. It  also  implies  the  use  of  a  larger  digestion  flask.  In  fact, 
it  is  now  quite  universal  to  make  the  digestion  in  a  special  glass 
flask  large  enough  to  be  used  also  for  the  distillation.  This 
saves  one  transfer  of  the  material  with  the  possible  danger  of  loss 
attending  it. 

In  the  distillation  it  is  a  common  practice,  especially  in  Ger- 
many, to  do  away  with  the  condensing  worm  and  to  carry  a  long 
glass  tube  from  the  distilling  flask  directly  into  the  acid  in  the 
receiver.  The  only  inconvenience  in  this  method  is  the  heating 
of  the  contents  of  the  receiving  flask,  but  this  is  attended  with 
no  danger  of  loss  of  ammonia  and  the  distillate,  on  account  of 
the  high  temperature  it  acquires,  is  left  free  of  carbon  dioxid. 
1  Zeitschrift  fur  analytische  Chemie,  1883  to  date. 


AGRICULTURAL   ANALYSIS 

Many  of  these  minor  changes  have  tended  to  simplify  the  pro- 
cess, but  without  affecting  the  principle  of  the  method  in  the 
least. 

2.  In  the  second  place  a  class  of  changes  may  be  mentioned  in 
which  there  is  a  marked  difference  in  the  method  of  effecting  the 
oxidation  secured  by  the  introduction  of  a  substance,  usually  a 
metal,  during  the  digestion  for  the  purpose  of  accelerating  the 
oxidation.     In  the   original   process   the   only   aid   to   oxidation 
was  applied  at  the  end  of  the  digestion  in  the  use  of  potassium 
permanganate.     In  the  modifications  now  under  consideration  a 
metallic  oxid  or  metal  is  applied  at  the  beginning  of  the  diges- 
tion.    Copper  and  mercury  are  the  metals  usually  employed.     A 
separate  paragraph  will  be  given  to  the  description  of  this  modi- 
fication known  as  the  process  of  Wilfarth. 

3.  The  third  class  of  changes  is  even  more  radical  in  its  nature, 
having  for  its  object  the  adaptation  of  the   moist  combustion 
method  to  oxidized  or  mineral  nitrogen.     The  chief  feature  of 
this  class  of  changes  consists  in  the  introduction  of  a  substance 
rich  in  hydrocarbons,  and  capable  of  easily  forming  nitro  com- 
pounds, for  the  purpose  of  holding  the  oxids  of  nitrogen  which 
are  formed  during  the  combustion  and  helping  finally  to  reduce 
them  to  the  form  of  ammonia.    The  chief  varieties  of  this  class 
of  changes  were  proposed  by  Asboth,  Jodlbauer,  and   Scovell, 
and  will  be  fully  set  forth  in  separate  paragraphs. 

313.  Method  of  Wilfarth. — The  basis  of  this  modification  as 
already  noted  rests  on  the  fact  that  certain  metallic  oxids  have 
the  power  of  carrying  oxygen  and  thus  assisting  in  a  catalytic 
way  in  the  combustion  of  organic  matter.2  The  copper  and  mer- 
cury oxids  are  best  adapted  for  this  purpose  and  experience  has' 
shown  that  mercuric  oxid,  or  even  metallic  mercury  gives  the 
best  results.  The  manipulation  is  carried  out  as  follows : 

From  one  to  three  grams  of  the  sample,  according  to  its  rich- 
ness in  nitrogen,  are  heated  with  a  mixture  of  20  cubic  centimeters 
of  acid  containing  two-fifths  fumfng  and  three-fifths  ordinary  sul- 
furic  acid.  To  this  is  added  about  seven-tenths  gram  of  mer- 
curic oxid  prepared  in  the  wet  way  from  a  mercury  salt  free  of 
*  Chemisches  Ceutral-Blatt,  1885  :  113. 


KJEU5AHL    METHOD  357 

nitrogen.  The  combustion  takes  place  in  the  usual  kjeldahl 
flask.  If  the  boiling  be  continued  until  the  liquid  is  entirely 
colorless,  final  oxidation  with  potassium  permanganate  is  unnec- 
essary. To  save  time  the  combustion  may  be  stopped  when  a 
light  amber  color  is  reached,  and  then  the  oxidation  finished  with 
permanganate.  Before  distilling,  a  sufficient  quantity  of  potas- 
sium sulfid  is  added  to  precipitate  all  the  mercury  as  sulfid  and 
thus  prevent  the  formation  of  mercurammonium  compounds 
which  would  produce  a  deficit  of  ammonia.  A  convenient  strength 
of  the  sulfid  solution  is  obtained  by  dissolving  40  grams  of  potas- 
sium sulfid  in  one  liter  of  water.  Bumping  at  the  end  of  the  dis- 
tillation is  not  usual,  especially  if  potash-lye  be  used,  but  should 
it  occur  it  may  be  stopped  by  the  addition  of  zinc  dust. 

Only  when  a  large  excess  of  potassium  sulfid  is  used  is  there 
an  evolution  of  hydrogen  sulfid,  the  presence  of  which,  however, 
does  not  influence  the  accuracy  of  the  results. 

The  presence  of  mercuric  sulfid  in  the  solution  tends  to  pre- 
vent bumping  during  the  distillation,  but  it  is  advisable,  never- 
theless, to  use  a  little  zinc  dust.  Other  minor  modifications  con- 
sist of  preparing  the  acid  mixture  with  equal  volumes  of  concen- 
trated and  fuming  sulfuric  acid  containing  in  one  liter  100  grams 
of  phosphoric  acid  anhydrid,  and  using  metallic  mercury  instead 
of  mercuric  oxid3 ;  or  a  mixture  of  half  a  gram  of  copper  sulfate 
and  one  gram  of  metallic  mercury ;  or  0.05  gram  of  copper  oxid 
and  five  drops  of  platinic  chlorid  solution  containing  0.04  gram 
of  platinum  in  a  cubic  centimeter.4 

314.  Kjeldahl  Method  as  Practiced  by  the  Holland  Royal  Ex- 
periment Station.5 — Necessary  Reagents:  i.  Phosphosulfuric 
acid,  made  by  mixing  a  liter  of  sulfuric  acid  of  specific  gravity 
1.84  with  200  grams  of  phosphoric  anhydrid. 

2.  Alkaline    sodium    sulfid   solution,   made   by   dissolving    500 
grams  of  sodium  hydroxid  and  six  grams  of  sodium  sulfid  or 
eight  and  one-half  grams  of  potassium  sulfid  in  a  liter  of  water. 

3.  Mercury. 

s  Kulisch,  Zeitschrift  fur  analytische  Chemie,  1886,  25  :  149. 

4  Ulsch,  Chemisches  Central-Blatt,  1886  :  375. 

5  Methoden  van  Onderzoek  aan  de  Rijkslandbouwproef stations  voor  het 
Jaar  1894. 


358  AGRICULTURAL  ANALYSIS 

4.  Paraffin  in  small  pieces. 

5.  Dilute  sulfuric  acid  and  dilute  potash  solution,  both  of  known 
strength. 

6.  Pieces  of  previously  ignited  pumice  stone  or  of  granulated 
zinc. 

7.  Neutral  solution  of  rosolic  acid  or  litmus. 

Apparatus. — The  necessary  apparatus  consists  of  oxidation 
flasks  of  about  200  cubic  centimeters  capacity  and  distillation 
flasks  of  about  500  cubic  centimeters  capacity,  both  of  Bohemian 
glass.  Copper  may  be  used  for  the  distillation  flasks. 

The  Process. — A  gram  of  the  sample  to  be  analyzed  is  placed 
in  an  oxidation  flask,  together  with  20  cubic  centimeters  of  phos- 
phosulfuric  acid  and  a  drop  of  mercury  (about  600  milligrams), 
and  heated  till  the  fluid  becomes  colorless.  After  cooling,  dilute 
and  wash  the  contents  of  the  flask  into  a  distillation  flask.  The 
resulting  volume  should  be  about  300  cubic  centimeters.  Add 
loo  cubic  centimeters  of  the  alkaline  sodium  sudfid  solution  and 
some  pieces  of  ignited  pumice  stone  or  granulated  zinc.  Distil 
the  ammonia,  receiving  the  distillate  in  a  flask  containing  a  known 
volume  of  the  standard  sulfuric  acid.  Titrate  with  tenth-normal 
potash,  using  litmus  or  rosolic  acid  as  indicator. 

315.  The  Kjeldahl  Method  as  Practiced  at  the  Halle  Station. 
—The  method  in  vogue  in  the  German  stations  of  conducting 
the  moist  combustion  process  is  well  illustrated  by  the 
method  of  procedure  followed  at  Halle.6  From  0.7  to  1.5 
grams  of  the  sample  are  used  for  analysis,  according  to  its  rich- 
ness in  nitrogen.  Because  of  the  fact  that  so  small  a  quantity 
of  the  sample  is  used,  it  is  of  the  highest  importance  that  it  be 
perfectly  homogeneous  throughout  its  entire  mass.  Otherwise, 
grave  errors  may  arise.  From  the  sample  as  sent  to  the  labo- 
ratory the  analyst  should  remove  a  subsample,  and  this  should  be 
rubbed  to  a  fine  powder  and  the  part  used  for  analysis  carefully 
selected  therefrom.  If  the  sample  be  moist  it  may  be  rubbed  up 
with  an  equal  weight  of  gypsum,  in  which  case  a  double  quantity 
is  employed  for  the  determination.  Substances  like  bone-meal, 

6  Bieler  und  Schneidewind,   Die  agricultur-chemische  Versuchsstation 
Halle  a/S.,  1892  :  34. 


KJELDAHIv    METHOD 


359 


which  do  not  keep  well  mixed,  especially  when  occasionally 
shaken,  should  be  intimately  mixed  before  each  weighing.  The 
sample  is  placed  in  a  glass  flask  of  about  150  cubic  centimeters 
capacity.  The  flask  should  be  made  of  a  special  glass  to  with- 
stand the  conditions  of  the  combustion.  A  globule  of  mercury 
weighing  a  little  less  than  one  gram  is  placed  in  the  flask  and 
also  20  cubic  centimeters  of  pure  sulfuric  acid  of  1.845  specific 
gravity.  The  mercury  is  conveniently  measured  by  an  apparatus 
suggested  by  Wrampelmayer.  It  consists  of  an  iron  tube  hold- 
ing mercury,  and  is  conveniently  filled,  from  time  to  time,  from 
a  supply  vessel  placed  in  a  higher  position  and  joined  by  means 
of  a  heavy  glass  tube  and  rubber  tube  connections.  The  lower 
end  of  the  iron  tube  is  provided  with  a  movable  iron  stopper 
having  a  pocket  just  large  enough  to  hold  a  globule  of  mercury, 
weighing  a  little  less  than  a  gram.  On  turning  the  stopper  the 
pocket  is  brought  opposite  a  discharge  orifice  and  the  measured 


Fig.  15.     Moist  Combustion  Apparatus  of  the  Halle  Agricultural  laboratory. 

globule  of  mercury  is  discharged.  With  substances  which  tend 
to  produce  a  strong  foaming  a  little  paraffin  is  used.  The  flasks 
after  they  are  charged  are  placed  on  circular  digesting  ovens 
under  a  hood,  as  shown  in  Fig.  15. 

At  first  the  tripodal  support  of  the  flasks  is  so  adjusted  as  to 
bring  them  between  the  lamps,  and  in  this  way  a  too  rapid  re- 
action is  at  first  avoided.  After  half  an  fiour  the  tripods  are  so 
turned  as  to  bring  each  flask  directly  over  the  lamp,  the  flame 
of  which  is  allowed  to  impinge  directly  against  the  glass.  The 
flame  is  so  regulated  that  after  the  evolution  of  the  sulfur  dioxid 


360  AGRICULTURAL   ANALYSIS 

has  nearly  ceased  the  contents  of  the  flask  are  brought  into  gentle 
ebullition.  The  boiling  is  continued  until  the  contents  of  the 
flask  are  colorless,  usually  about  two  hours.  As  a  rule,  such  sub- 
stances as  cottonseed-meal  and  dried  blood  will  take  a  longer 
time  for  complete  combustion  than  other  fertilizing  materials. 
During  the  combustion  the  flasks  are  closed  with  an  oblong  loose- 
fitting  unground  glass  stopper.  When  the  oxidation  is  finished 
the  contents  of  the  flasks  are  allowed  to  cool,  the  stoppers  are  re- 
moved, and  enough  water  is  added  to  fill  the  flasks  about  three- 
quarters  full.  The  flasks  are  gently  shaken,  and  the  possibility  of 
breaking  from  the  heat  developed  must  not  be  overlooked.  To 
avoid  confusion,  the  flasks  are  all  numbered  before  beginning  the 
work  and  the  numbers  noted  by  the  analyst  in  connection  with 
the  samples.  The  contents  of  each  one  are  next  poured  into  the 
distillation  flask  and  the  digestion  vessels  are  washed  with  100 
cubic  centimeters  of  water  in  three  portions  and  the  wash-water 
added  to  the  liquid.  Sometimes  in  washing  out  the  digestion 
flask  yellow  basic  mercury  compounds  separate  on  its  walls,  but 
this  does  not  in  any  way  influence  the  accuracy  of  the  results. 
The  distillation  flasks  should  have  about  600  cubic  centimeters 
capacity.  To  avoid  the  transfer,  the  digestion  may  take  place  in 
the  distillation  flask,  in  which  case  the  latter  must  be  made  of 
special  glass  as  indicated. 

To  the  liquid  thus  transferred  are  added  75  cubic  centimeters 
of  soda-lye,  containing  one  and  one-half  times  as  much  potas- 
sium Ftilfid  as  is  necessary  to  combine  with  the  mercuric  sulfate 
present.  The  lye  is  of  such  a  strength  that  60  cubic  centimeters 
are  sufficient  to  neutralize  the  acid  present.  It  has  a  specific 
gravity  of  1.375  an<^  contains  33  grams  of  potassium  sulfid  in 
a  liter. 

In  order  to  avoid  the  bumping  which  may  take  place  during 
the  distillation,  some  granulated  zinc  should  be  added. 

The  distillation  flask  is  closed  with  a  rubber  stopper  carrying 
a  bulb-tube  which  ends  above  in  a  glass  tube  about  three-quar- 
ters of  a  meter  long,  bent  at  an  acute  angle  and  passing  obliquely 
downward  on  a  convenient  support.  This  tube  is  connected  by  a 
rubber,  with  the  end  tube  bent  nearly  at  a  right  angle  and  dip- 


KJELDAHL    METHOD 


361 


ping  into  the  standardized  acid  in  the  erlenmeyer  receiver.  The 
general  arrangement  of  the  distilling  apparatus  is  shown  in 
Fig.  1 6.  Since  the  contents  of  the  vessel  are  warmed  by  mixing 
with  the  soda-lye,  the  flame  can  be  turned  on  at  full  head  at  once 
at  the  commencement  of  the  operation.  In  about  a  quarter  of 
an  hour  the  liquid  in  the  receiver  will  be  at  the  boiling-point, 
and  the  boiling  should  be  continued  for  five  minutes  more,  making 
20  minutes  in  all  for  the  completion  of  the  distillation.  By  this 
boiling  the  contents  of  the  receiver  are  not  charged  with  carbon 
dioxid,  as  might  happen  if  a  condenser  were  used.  The  receiver 
contains  20  cubic  centimeters  of  a  standardized  sulfuric  acid  solu- 
tion and  about  50  cubic  centimeters  of  water. 

The  acid  used  should  contain  38.1  grams  of  sulfuric  acid  of 
1.845  specific  gravity  in  a  liter;  and  it  should  be  set  by  titration 


Fig.  16.    Distillation  Apparatus  of  the  Halle  Agricultural  Laboratory. 

with  chemically  pure  sodium  carbonate.  For  this  purpose  0.7 
gram  of  sodium  carbonate  is  heated  in  a  platinum  crucible  for 
two  hours  over  a  small  flame,  weighed,  and  placed  in  an  erlen- 
meyer together  with  20  cubic  centimeters  of  the  sulfuric  acid, 
care  being  taken  to  avoid  loss  from  the  vigorous  evolution  of 
carbon  dioxid.  After  boiling  for  10  minutes  all  the  carbon  dioxicl 
is  removed  from  solution.  After  cooling,  the  excess  of  acid  is 
determined  by  titration  with  a  standardized  barium  hydroxid 
solution,  using  rosolic  acid  as  indicator. 

The  solution  of  barium  hydroxid  is  made  as  follows:  Digest, 
with  warm  water,  260  grams  of  caustic  baryta,  Ba(OH),,  until 
it  is  nearly  all  dissolved,  filter,  and  make  up  to  a  volume  of  10 


362  AGRICULTURAL  ANALYSIS 

liters  and  keep  in  a  flask  free  of  carbon  dioxid.  A  solution  of 
barium  hydroxid  is  to  be  preferred  to  the  corresponding  sodium 
compound  for  titration.  If  traces  of  carbonate  be  formed  in  the 
two  liquids,  the  sodium  salt  will  remain  in  solution  while  the 
barium  compound  will  settle  at  the  bottom  of  the  flask. 

The  Indicator. — The  indicator  used  to  determine  the  end  of 
the  reaction  is  made  by  dissolving  one  gram  of  rosolic  acid  in 
50  cubic  centimeters  of  alcohol.  From  one  to  two  drops  are 
enough  for  each  titration.  The  color  reaction  is  less  definite  as 
the  quantity  of  ammonia  in  the  liquid  increases.  When  the  titra- 
tion solutions  have  been  prepared  as  above  described  it  is  found 
to  require  about  90  of  the  barium  hydroxid  to  neutralize  20  cubic 
centimeters  of  the  sulfuric  acid. 

By  direct  titration  with  sodium  carbonate  it  is  ascertained  how 
many  grams  of  nitrogen  the  20  cubic  centimeters  of  sulfuric  acid 
represent. 

Example. — Suppose  the  weight  of  the  dried  sodium  carbonate 
prepared  as  above  directed  is  0.6989  gram. 
i/2Na2CO3,  i/2N2 

Then  0.6989     :     53  —  x     :       14 

Whence  x  =  0.184615  gram  of  nitrogen. 

Suppose  further  that  20  cubic  centimeters  of  sulfuric  acid 
solution  require  94  cubic  centimeters  of  barium  hydroxid  for  com- 
plete saturation  and  after  treatment  with  the  above  amount  of 
sodium  carbonate,  10^2  cubic  centimeters  of  the  barium  solution 
to  neutralize  the  remaining  acid. 

Then  94—10.5=83.5 

And  0.184615  :  83-5=x:94. 

Whence  x  =  0.207830  gram  of  nitrogen  corresponding  to  20 
cubic  centimeters  of  the  sulfuric  acid  used. 

Then  0.20783-^94  =  0.002211  gram  of  nitrogen  correspond- 
ing to  one  cubic  centimeter  of  the  barium  hydroxid  solution. 

If  then  in  the  analysis  of  a  fertilizer  it  is  found  that  60.5  cubic 
centimeters  are  required  to  neutralize  the  excess  of  sulfuric  acid 
after  distillation,  the  percentage  of  nitrogen  in  the  sample  is  found 
as  follows : 


OFFICIAL    KJEXDAHL    METHOD  363 

60.5X0.002211=0.13377. 

0.20783 — o.  1 3377=0.07406. 

o.o74o6Xioo=7.4o6=per  cent,  nitrogen  in  sample  when  one 
gram  is  used  for  the  combustion. 

316.  The  Official  Kjeldahl  Method.  Not  Applicable  in  the 
Presence  of  Nitrates. — In  order  to  determine  if  the  sample  con- 
tains nitric  acid  or  nitrates,  apply  the  following  test:7 

Mix  five  grams  of  the  fertilizer  with  25  cubic  centimeters  of 
hot  water  and  filter.  To  a  portion  of  this  solution  add  two  vol- 
umes of  concentrated  sulfuric  acid,  free  from  nitric  acid  and 
oxids  of  nitrogen,  and  allow  the  mixture  to  cool.  Add  cautiously 
a  few  drops  of  concentrated  solution  of  ferrous  sulfate,  so  that 
the  fluids  do  not  mix.  If  nitrates  are  present  the  junction  shows 
at  first  a  purple,  afterwards  a  brown  color,  or  if  only  a  very 
minute  quantity  be  present,  a  reddish  color.  To  another  por- 
tion of  the  solution  add  one  cubic  centimeter  of  dilute  solution  of 
nitrate  of  soda  (three  grams  to  300  cubic  centimeters)  and  test 
as  before  to  determine  whether  sufficient  sulfuric  acid  was  added 
in  the  first  test. 

Preparation  of  Reagents. —  (i)  Acids. — (a)  Standard  hydro- 
chloric acid,  the  absolute  strength  of  which  has  been  determined 
by  precipitating  with  silver  nitrate,  and  weighing  the  silver  chlo- 
rid  as  follows  :8 

To  any  convenient  quantity  of  the  acid  to  be  standardized, 
add  a  solution  of  silver  nitrate  in  slight  excess,  and  two  cubic  cen- 
timeters of  pure  nitric  acid,  of  specific  gravity  1.2.  Heat  to 
boiling-point,  and  keep  at  this  temperature  for  some  minutes 
without  allowing  violent  ebullition,  constantly  stirring  until 
the  precipitate  assumes  the  granular  form.  Allow  to  cool 
somewhat,  and  then  filter  the  fluid  through  asbestos.  Wash 
the  precipitate  by  decantation,  with  200  cubic  centimeters  of  very 
hot  water,  to  which  have  been  added  eight  cubic  centimeters 
of  nitric  acid  and  two  cubic  centimeters  of  dilute  solution  of  silver 
nitrate  containing  one  gram  of  the  salt  in  100  cubic  centimeters 
of  water.  The  washing  by  decantation  is  performed  by  adding 

7  Division  of  Chemistry,  Bulletin  49,  1897  :  19. 

8  Division  of  Chemistry,  Bulletin  46,  Revised  Edition,  1899  :  14. 


364  AGRICULTURAL  ANALYSIS 

the  hot  mixture  in  small  quantities  at  a  time,  and  beating  up  the 
precipitate  well  with  a  thin  glass  rod  after  each  addition.  The 
pump  is  kept  in  action  all  the  time,  but  to  keep  out  dust  during 
the  washing,  the  cover  is  only  removed  from  the  crucible  when 
the  fluid  is  to  be  added. 

Put  the  vessels  containing  the  precipitate  aside,  return  the  wash- 
ings once  through  the  asbestos  so  as  to  obtain  them  quite  clear, 
remove  them  from  the  receiver,  and  set  aside  to  recover  the  excess 
of  silver.  Rinse  the  receiver  and  complete  the  washing  of  the  pre- 
cipitate with  about  200  cubic  centimeters  of  cold  water.  Half 
of  this  is  used  to  wash  by  decantation  and  the  remainder  to 
transfer  the  precipitate  to  the  crucible  with  the  aid  of  a  trimmed 
feather.  Finish  washing  in  the  crucible,  the  lumps  of  silver 
chlorid  being  broken  down  with  a  glass  rod.  Remove  the 
second  filtrate  from  the  receiver  and  pass  about  20  cubic  centi- 
meters of  98  per  cent,  alcohol  through  the  precipitate.  Dry  at 
from  140°  to  150°.  Exposure  for  half  an  hour  is  found  more 
than  sufficient,  at  this  temperature,  to  dry  the  precipitate  thor- 
oughly. It  has  been  proposed  to  modify  this  process  somewhat 
by  directing  that  the  precipitate  be  washed  several  times  by  de- 
cantation instead  of  with  200  cubic  centimeters  of  water,  this 
quantity  not  being  considered  sufficient  in  all  cases. 

The  above  is  the  old  method  of  standardizing  the  hydrochloric 
acid.  The  method  now  in  use  is  as  follows :° 

By  means  of  a  preliminary  test  with  silver-nitrate  solution, 
to  be  measured  from  a  burette,  with  excess  of  calcium  carbon- 
ate to  neutralize  free  acid  and  potassium  chromate  as  indicator, 
determine  exactly  the  amount  of  nitrate  required  to  precipitate 
all  the  hydrochloric  acid.  To  a  measured  and  also  weighed  por- 
tion of  the  standard  acid  add  from  a  burette  one  drop  more  of 
silver-nitrate  solution  than  is  required  to  precipitate  the  hydro- 
chloric acid.  Heat  to  boiling,  cover  from  the  light,  and  allow 
to  stand  until  the  precipitate  is  granular.  Then  wash  with  hot 
water  through  a  gooch  crucible,  testing  the  filtrate  to  prove  ex- 
cess of  silver  nitrate.  Dry  the  silver  chlorid  at  140°  to  150°  C. 

(6)     Standard  sulfuric  acid,  the  absolute  strength  of  which  has 
9  Bureau  of  Chemistry,  Bulletin  107,  1907  :  5. 


OFFICIAL    KJELDAHL    METHOD  365 

been  determined  by  precipitation  with  barium  chlorid  and  weigh- 
ing the  resulting  barium  sulfate : 

For  ordinary  work  half-normal  acid  is  recommended,  i.  e., 
containing  24.52  grams  sulfuric  acid  to  the  liter ;  for  determining 
very  small  amounts  of  nitrogen,  one-tenth  normal  acid  is  recom- 
mended. In  titrating  mineral  acids  against  ammonia  solutions, 
use  cochineal  as  indicator. 

(c)  Sulfuric  acid,  specific  gravity  1.84,   free  of  nitrates  and 
also   of  ammonium    sulfate,   which   is   sometimes   added   in   the 
process  of  manufacture  to  destroy  nitrogen  oxids. 

(d)  Standard  alkali,  the  strength  of  which,   relative  to  the 
acid,  has  been  accurately  determined.     One-tenth  normal  ammo- 
nia solution,  i.  ?.,  containing  1.7051  grams  of  ammonia  to  the 
liter,  is  recommended  for  accurate  work. 

(e)  Metallic  mercury  or  mercuric  oxid,  prepared  in  the  wet 
way.     That  prepared  from  mercuric  nitrate  can  not  be  safely 
used. 

(/)  Potassium  permanganate  finely  pulverized. 

(g)  Granulated  sine,  pumice  stone,  or  sine  dust  (one-half 
gram)  is  to  be  added  to  the  contents  of  the  flask  during  distillation, 
when  found  necessary,  in  order  to  prevent  bumping. 

In  the  laboratory  of  the  Bureau  of  Chemistry,  zinc  dust  is  no 
longer  used,  since  its  use  tends  to  break  the  flask.  Pumice  stone 
is  also  no  longer  used,  since  experience  has  shown  that  granulated 
zinc  is  best  suited  to  secure  the  purpose  intended. 

(h)  Potassium  sulfid. — A  solution  of  40  grams  of  commercial 
potassium  sulfid  in  one  liter  of  water. 

(»)  Soda. — A  saturated  solution  of  sodium  hydroxid  free  of 
nitrates. 

(/)  Indicator. — A  solution  of  cochineal  prepared  as  follows : 
Digest  for  a  day  or  two  at  ordinary  temperatures  and  with  fre- 
quent agitation,  three  grams  of  pulverized  cochineal  in  a  mixture 
of  50  cubic  centimeters  of  strong  alcohol  with  200  cubic  centi- 
meters of  distilled  water.  The  filtered  solution  is  employed. 

Apparatus. —  (i)  Kjeldahl  digestion  flasks,  pear-shaped,  round 
bottom,  of  hard,  moderately  thick,  well-annealed  glass:  These 
flasks  are  about  22  centimeters  long,  having  a  maximum  diame- 


366  AGRICULTURAL   ANALYSIS 

ter  of  six -centimeters  and  tapering  out  gradually  in  a  long  neck, 
which  is  two  centimeters  in  diameter  at  the  narrowest  part,  and 
flared  a  little  at  the  edge.  The  total  capacity  is  about  250  cubic 
centimeters. 

(2)  Distillation  flasks. — For  distillation,   a   flask  of  ordinary 
shape,  of  about  550  cubic  centimeters  capacity  may  be  used.     It 
is  fitted  with  a  rubber  stopper  and  with  a  bulb-tube  above  to  pre- 
vent the  possibility  of  sodium  hydroxid  being  carried  over  me- 
chanically during  distillation.     The  bulbs  are  about  three  centi- 
meters in  diameter,  the  tubes  being  of  the  same  diameter  as  the 
condenser  and  cut  off  obliquely  at  the  lower  end,  which  is  fastened 
to  the  tube  of  the  condenser  by  a  rubber  tube. 

(3)  Kjeldahl  flasks  for  both  digestion  and  distillation. — These 
are  pear-shaped,  round-bottom  flasks,  having  a  total  capacity  of 
about  550  cubic  centimeters,  made  of  hard,  moderately  thick  and 
well-annealed  glass.     When  used  for  distillation  the  flasks  are 
fitted  with  rubber  stoppers  and  bulb-tubes,  as  given  under  distil- 
lation flasks. 

Manipulation. —  (i)  The  Digestion. — From  seven-tenths  to 
three  and  five-tenths  grams  of  the  substance  to  be  analyzed,  ac- 
cording to  its  proportion  of  nitrogen,  are  brought  into  a  digestion 
flask  with  approximately  seven-tenths  gram  of  mercuric  oxid  or 
its  equivalent  in  metallic  mercury  and  20  cubic  centimeters  of 
sulfuric  acid.  The  flask  is  placed  in  an  inclined,  position,  and 
heated  below  the  boiling-point  of  the  acid  for  from  five  to  15 
minutes  or  until  frothing  has  ceased.  If  the  mixture  froths 
badly,  a  small  piece  of  paraffin  may  be  added  to  prevent  it. 
The  heat  is  then  raised  until  the  acid  boils  briskly.  No  further 
attention  is  required  until  the  contents  of  the  flask  have  become 
a  clear  liquid,  which  is  colorless  or,  at  least,  has  only  a  very  pale 
straw  color.  The  flask  is  then  removed  from  the  frame,  held 
upright  and,  while  still  hot,  potassium  permanganate  is  dropped 
in  carefully  and  in  small  quantities  at  a  time  until,  after  shak- 
ing, the  liquid  remains  of  a  green  or  purple  color.  Respecting 
the  time  of  boiling,  it  is  suggested  that  the  following  be  added  to 
the  official  methods  in  place  of  the  sentence  beginning  "no 
further  attention,  etc."  "Boil  for  at  least  one  hour  or  until  the 


368  AGRICULTURAL   ANALYSIS 

in  order  to  give  a  better  view  of  the  arrangement  of  the  fur- 
nace. In  the  furnace  there  are  three  sets  of  eight  digestion  flasks. 
The  neck  of  each  flask  is  held  by  an  opening  into  a  lead  tube  of 
five  inches  diameter,  connected  with  a  ventilating  flue  concealed 
by  the  tube  in  the  photograph.  Any  sulfuric  acid  which  con- 
denses in  this  tube  is  caught  by  a  vessel  placed  under  the  lowest 
part  of  the  lead  tube ;  the  volatile  products  escape  in  the  flue. 

318.  The  Distillation  Apparatus  in  Use  in  the  Laboratory  of 
the  Bureau  of  Chemistry. — In  the  nitrogen  laboratory  of  the  Bu- 
reau the  distilling  apparatus  is  arranged  as  shown  in  Fig.  18.  The 
flasks  are  the  same  as  are  used  in  the  digestion  process.  They  are 
connected  to  the  block  tin  condensers  by  the  trap  shown  in  Fig.  19. 
The  block  tin  condensers  are  contained  in  an  iron  tube  through 
which  cold  water  flows  during  the  distillation.  The  trap  (Fig.  19) 
above  the  flask  carries  an  emergent  tube  which  extends  to  near- 
ly the  center  of  the  trap  and  is  bent  laterally  to  avoid  any  danger 
of  carrying  over  any  alkali  that  may  be  projected  into  the  trap 
during  boiling.     A  small  hole  near  the  bottom  allows  any  con- 
densed steam  to  flow  back  into  the  distilling  flask.     The  cold 
water  enters  the  condensers  through  the  pipe  provided  with  a  stop- 
cock shown  in  the  center,  and  leaves  by  the  two  pipes  shown  at 
the  sides   of  the  apparatus.     The  boiling   is   continued   usually 
for  nearly  an  hour,  or  until  bumping  begins.       The  table  on 
•which  the  apparatus  is  placed  is  so  arranged  as  to  permit  of 
easy  access  on  all  sides.     The  standard  acid  is  held  in  erlen- 
meyers    placed     on     wooden  blocks  so  that  the  end  of  the  con- 
denser, which  is  a  drawn-out  glass  tube,  dips  beneath  the  surface 
•of  the  acid. 

319.  Patrick's  Distilling  Flask. — To    avoid    the    expense    and 
annoyance  attending  the  breaking  of  the  distilling  flasks,  Patrick 
has  proposed  to  make  them  of  copper.10     The  size,  about  half  a 
liter,  made  for  the  evolution  of  oxygen  for  experimental  pur- 
poses, may  be  used.     A  little  excess  of  potassium  sulfid  is  used 
tc  make  up  for  any  of  it  which  might  be  consumed  by  the  cop- 
per.    About   25   cubic   centimeters   of  this  solution  are   recom- 
mended. No  zinc  or  pumice  stone  is  required  to  prevent  bumping, 

10  Division  of  Chemistry,  Bulletin  31,  1891  :  142. 


DISTILLATION  APPARATUS 


369 


Fig.  19.    Trap  of  Distilling  Apparatus. 


37°  AGRICULTURAL   ANALYSIS 

and  the  distillation  may  be  finished  within  30  minutes,  thus  secur- 
ing a  saving  of  time.  There  will  doubtless  be  a  slight  corro- 
sion of  the  flasks  by  the  sulfid  employed,  but  where  the  gunning 
oxidation  process  is  practiced  this  danger  would  be  avoided. 

320.  The  Gunning  Moist  Combustion  Process. — The  modifi- 
cation proposed  by  Gunning  was  based  upon  the  observation  that 
in  the  ordinary  kjeldahl  process  the  excess  of  sulfur  trioxid  in 
the  beginning  of  the  operation  soon  escapes  or  unites  with  water 
in  a  form  not  easily  decomposed.11  During  the  progress  of  the 
combustion  the  acid  diminishes  in  strength  until  it  is  below  the 
concentration  represented  by  the  formula  H2SO4,  and  in  this 
diluted  condition  the  oxidation  takes  place  more  slowly.  Gun- 
ning proposes  to  avoid  this  difficulty  by  mixing  potassium  sulfate 
with  the  sulfuric  acid.  This  salt  forms  with  the  sulfuric  .acid, 
acid  salts  which,  by  heating,  lose  water  easier  than  acid,  and,  as 
is  well  known,  they  not  only  act  as  decomposing  and  oxidizing 
media  as  well  as  sulfuric  acid,  but  even  in  a  higher  degree,  re- 
sembling the  action  of  sulfuric  acid  at  high  temperatures  and 
under  pressure. 

By  heating  this  mixture  of  sulfuric  acid  and  potassium  sulfate 
with  organic  matters  in  an  open  vessel,  not  only  the  water  origi- 
nally present,  but  that  which  is  formed  during  the  oxidation,  is 
driven  off  without  loss  of  acid.  For  this  reason  instead  of  the 
oxidizing  mixture  becoming  weaker,  the  acid  becomes  stronger, 
the  boiling-point  rises  and  this,  combined  with  the  fluidity  of 
the  mass,  favors  the  decomposition  and  oxidation  of  the  organic 
matter  in  a  constantly  increasing  ratio. 

The  original  mixture  used  by  Gunning  has  the  following  com- 
position; viz.,  one  part  of  potassium  sulfate  and  two  parts  of 
strong  sulfuric  acid.  The  substances  are  united  by  heat,  and 
on  cooling  are  in  a  semi-solid  state,  melting,  however,  easily  on 
the  application  of  heat  and  assuming  a  condition  that  permits 
them  to  be  poured  from  vessel  to  vessel.  The  quantity  of  the 
sample  should  vary  in  proportion  to  its  nitrogenous  content  from 
half  a  gram  to  a  gram.  The  combustion  takes  place  in  flasks  en- 
tirely similar  to  those  used  in  the  ordinary  kjeldahl  process.  In  the 
11  Zeitschrift  fur  analytische  Chemie,  1889,  28  :  188. 


REACTIONS  OF  THE  GUNNING  PROCESS  371 

case  of  liquids,  they  should  be  previously  evaporated  to  dryness 
before  the  addition  of  the  oxidizing  mixture.  At  the  beginning 
of  the  combustion  there  is  a  violent  foaming,  attended  with  evo- 
lution of  some  acid  and  much  water,  and  afterwards  of  stronger 
acid.  This  loss  of  acid  should  not  be  allowed  to  go  far  enough 
to  produce  too  great  concentration  of  the  material  in  the  flask. 
One  of  the  best  ways  to  avoid  it,  is  to  place  a  funnel  in  the 
flask  covered  with  a  watch-glass,  which  will  permit  of  the  con- 
densation and  return  of  the  escaping  acid.  As  soon  as  the  foam- 
ing ceases,  the  flame  should  be  so  regulated  as  to  permit  of  the 
volatilized  acid  being  condensed  upon  the  sides  of  the  flask.  In 
the  end  a  colorless  mass  is  obtained  in  which  no  metallic  oxids 
are  present,  and  this  mass  can  at  once  be  diluted  with  water, 
treated  with  alkali,  and  distilled.  According  to  the  nature  of 
the  substance,  from  half  an  hour  to  an  hour  and  a  half  are  re- 
quired for  the  complete  combustion. 

Modifications  of  the  Gunning  Method. — As  in  the  case  of  the 
kjeldahl  method,  numerous  minor  modifications  of  the  gunning 
method  have  been  made,  the  most  important  of  which  relate  to 
its  application  to  substances  containing  nitrates.  In  general  the 
same  processes  are  employed  in  this  case  as  with  the  kjeldahl 
method.  One  of  the  best  modifications  consists  in  the  use  of  the 
mixture  of  salicylic  and  sulfuric  acids,  followed  by  the  addition 
of  sodium  thiosulfate  or  of  potassium  sulfate  or  sulfid.  These 
modifications  will  be  given  in  detail  under  the  official  methods. 

321.  Reactions  of  the  Gunning  Process. — The  various  reac- 
tions which  take  place  during  the  combustion  according  to  the 
gunning  method  have  been  tabulated  by  Van  Slyke.12 

The  first  reaction  to  take  place  is  the  union  of  sulfuric  acid 
and  potassium  sulfate  to  form  potassium  acid  sulfate  in  accord 
ance  with  the  following  equation: 

(i)   K2SO4+H2SO4=2KHSO4. 

When  heated,  the  potassium  acid  sulfate  decomposes,  forming 
potassium  disulfate  and  water,  thus : 

(2)  2KHSO4r=K2S2O7-fH2O. 

"  Division  of  Chemistry,  Bulletin  35,  1892   :  68. 


372  AGRICULTURAL  ANALYSIS 

The  potassium   disulfate   at   a   higher   temperature   decomposes, 
forming  normal  potassium  sulfate  and  sulfur  trioxid,  thus: 

(3)   K2S207=K2S04+S03. 

At  a  sufficiently  high  temperature  the  two  preceding  reactions 
may  take  place  in  one,  thus: 

2KHSO4=K2SO4+H2O+SO3. 

At  the  temperature  at  which  these  reactions  take  place,  the 
water  that  is  set  free  does  not  recombine  with  the  sulfur  trioxid 
nor  with  the  sulfuric  acid  that  is  present  in  excess,  but  is  ex- 
pelled from  the  mixture ;  hence  the  mixture  becomes  more  con- 
centrated during  the  digestion.  The  sulfur  trioxid  set  free  acts 
upon  the  organic  matter  in  the  powerful  manner  peculiar  to  it, 
and  the  potassium  sulfate,  formed  in  the  last  reaction  above,  unites 
with  another  molecule  of  sulfuric  acid,  and  the  same  round  of  re- 
actions is  repeated  continuously  so  long  as  there  is  an  excess  of 
free  sulfuric  acid  present  in  the  mixture.  As  the  liquid  becomes 
more  concentrated  with  the  continuation  of  the  digestion,  the 
boiling-point  increases  so  that  the  effect  is  the  same  as  heating 
under  pressure.  The  danger  of  too  great  concentration  and  risk 
of  consequent  loss  of  nitrogen  is  avoided  by  using  increased  pro- 
portions of  sulfuric  acid. 

As  compared  with  the  kjeldahl,  the  gunning  method  presents 
the  following  advantages : 

1 i )  The  gunning  method  requires  fewer  reagents.     As  no  form 
of  mercury  is  used,  no  potassium  sulfid  is  needed,  and  there  is  no 
risk  of  loss  from  the  presence  of  mercurammonium  compounds. 

(2)  The  solution  to  which  caustic  soda  is  added  is  clear,  so 
that  in  neutralizing  it  is  an  easy  matter  to  avoid  great  excess  of 
alkali,  and  so,  in  most  cases,  to  avoid  foaming  and  bumping  in 
distillation. 

(3)  In  the  blank  determinations  less  nitrogen  is  found  in  the 
reagents  used  in  the  gunning  method.     In  only  one  case  was 
more  nitrogen  reported  in  a  blank  by  this  method  than  in  the 
other  methods;  in  all  the  others  the  amount  was  considerably 
less. 

322.  The  Official  Gunning  Method.13 — In  a  digestion  flask  hold- 
'  1S  Bureau  of  Chemistry,  Bulletin  107,  1907  :  7. 


MODIFICATIONS  OF  ASBOTH  373 

ing  from  250  to  550  cubic  centimeters,  place  from  0.7  to  3.5 
grams  of  the  substance  to  be  analyzed,  according  to  its  propor- 
tion of  nitrogen.  Add  10  grams  of  powdered  potassium  sulfate 
and  from  15  to  25  cubic  centimeters  (ordinarily  about  20  cubic 
centimeters)  of  concentrated  sulfuric  acid.  Conduct  the  diges- 
tion as  in  the  kjeldahl  process,  starting  with  a  temperature  be- 
low boiling-point  and  increasing  the  heat  gradually  until  all  froth- 
ing ceases.  Digest  until  colorless  or  nearly  so.  Do  not  add  either 
potassium  permanganate  or  potassium  sulfid.  Dilute,  neutralize, 
and  distil  as  in  the  kjeldahl  method.  In  neutralizing,  it  is  conven- 
ient to  add  a  few  drops  of  phenolphthalein  indicator,  by  which  one 
can  tell  when  the  acid  is  completely  neutralized,  remembering 
that  the  pink  color,  which  indicates  an  alkaline  reaction,  is  de- 
stroyed by  a  considerable  excess  of  strong  fixed  alkali.  The  dis- 
tillation and  titration  are  conducted  as  in  the  kjeldahl  method. 
In  distilling,  the  use  of  zinc  or  of  some  substance  to  prevent 
bumping  or  foaming  is  generally  necessary.  The  amount  of  sul- 
furic acid  recommended  by  Gunning  is  two  grams  for  each  gram 
of  potassium  sulfate ;  but  Van  Slyke  has  found  that  this  mixture 
is  so  viscous  as  to  cause  troublesome  foaming  frequently,  and 
after  cooling  it  cakes  in  a  hard  mass,  which  may  be  difficult  to 
redissolve.14  To  avoid  foaming  and  caking,  he  has  found  it  an 
effective  means  to  increase  the  amount  of  sulfuric  acid  used, 
using  instead  of  two  grams  to  one  of  potassium  sulfate,  three  or 
four  grams  of  acid  to  one  of  potassium  sulfate.  It  is,  therefore, 
suggested  in  carrying  out  the  work,  to  use  from  five  to  25  cubic 
centimeters  (ordinarily  about  20  cubic  centimeters)  of  sulfuric 
acid  for  10  grams  of  potassium  sulfate.  In  case  the  potassium 
sulfate  is  not  free  from  nitrogen  compounds,  one  or  two  recrys- 
tallizations  will  make  it  pure. 

CHANGES  IN  KJELDAHL  METHOD  TO  INCLUDE  NITRIC  ACID 

323.  Modifications   of  Asboth. — In  order  to  adapt  the  moist 

combustion  process  to  nitric  nitrogen  Asboth  proposed  the  use  of 

benzoic  acid.15     For  half  a  gram  of  saltpeter  1.75  grams  of  ben- 

u  Division  of  Chemistry,  Bulletin  35,  1892  :  68. 

15  Chemisches  Central-Blatt,  1886  :  161. 


374  AGRICULTURAL   ANALYSIS 

zoic  acid  should  be  used.  At  the  end  of  the  combustion  the  re- 
sidual benzoic  acid  is  oxidized  by  means  of  potassium  perman- 
ganate with  a  subsequent  reheating.  If  the  nitrogen  be  present 
as  an  oxid  or  as  cyanid,  one  gram  of  sugar  is  added.  The  me- 
tallic element  added  is  half  a  gram  of  copper  oxid.  Asboth  also 
recommends  that  the  soda-lye  used  in  the  distillation  be  mixed 
with  sodium  potassium  tartrate  for  the  purpose  of  holding  the 
copper  and  manganese  oxids  in  solution  and  thus  preventing 
bumping.  The  alkaline  liquor  contains  in  one  liter  350  grams 
of  the  double  tartrate  and  300  grams  of  sodium  hydroxid. 

The  principle  on  which  the  use  of  benzoic  acid  rests  is  found 
in  the  fact  that  it  easily  yields  nitro-compounds  and  thus  pre- 
vents the  loss  of  the  nitrogen  oxids,  these  readily  combining 
with  the  benzoic  acid.  The  nitro-compounds  can  be  subsequently 
converted  into  ammonia  by  treatment  with  potassium  perman- 
ganate. 

The  pyridin  and  chinolin  groups  of  bodies  do  not  yield  all  their 
nitrogen  as  ammonia  by  the  above  treatment. 

The  conclusions  drawn  by  Asboth  from  the  analytical  data  ob- 
tained are: 

(1)  Sugar  should  be  used  in  the  ordinary  kjeldahl  process  in 
those  cases  where  the  nitrogen  in  the  organic  substance  is  pres- 
ent as  oxids  or  as  cyanogen. 

(2)  In  the  case  of  nitrates  good  results  may  be  secured  with 
benzoic  acid  but  permanganate  must  be  added  at  the  end. 

(3)  The  kjeldahl-wilfarth  process  can  be  applied   with  sub- 
stances difficultly  decomposed,  e.  g.,  alkaloidal  bodies. 

324.  Variation  of  Jodlbauer. — The  benzoic  acid  method,  al- 
though a  step  forward,  is  not  entirely  satisfactory  in  the  treat- 
ment of  nitrates  by  moist  combustion.  Jodlbauer  has  proposed  to 
substitute  for  the  benzoic,  phenolsulfuric  acid.10 

From  two-  to  five-tenths  gram  of  a  nitrate  are  treated  with 
20  cubic  centimeters  of  concentrated  sulfuric  and  two  and  a 
half  of  phenolsulfuric  acid,  together  with  three  grams  of  zinc 
dust  and  five  drops  of  a  solution  of  platinic  chlorid  of  the  strength 
mentioned  above.  The  phenolsulfuric  acid  is  prepared  by  dis- 
18  Chemisches  Central-Blatt,  1886  :  433. 


DUTCH   JODLBAUER   METHOD  375 

solving  50  grams  of  phenol  in  100  cubic  centimeters  of  strong 
sulfuric  acid.  The  combustion  is  continued  until  the  solution  is 
colorless,  which  may  take  as  much  as  five  hours.  If  phosphoric 
anhydrid  be  used  the  time  of  the  combustion  may  be  diminished 
by  one-half,  but  in  such  a  case  the  glass  of  the  combustion  flask 
is  strongly  attacked  and  is  quite  likely  to  break. 

When  the  substances  used  are  very  rich  in  nitrates,  it  is  advis- 
able to  rub  them  first  with  dry  gypsum. 

The  theory  of  the  process  rests  on  the  fact  that  by  a  careful 
admixture  of  a  nitrogenous  substance  diluted  with  land  plaster 
with  phenolsulfuric  acid,  it  is  possible  to  change  the  nitric  acid 
into  nitro-phenol,  and  by  the  reducing  action  of  zinc  dust  to  change 
the  nitro-product  formed  into  amido-phenol.  This  afterwards 
is  transformed  into  ammonium  sulfate  by  heating  with  sulfuric 
acid,  by  which  process,  at  the  same  time,  all  other  nitrogenous 
compounds  present  in  the  substance,  as  with  Kjeldahl's  method, 
likewise  form  ammonium  sulfate,  only  with  the  difference  that 
addition  of  mercury  is  here  absolutely  necessary  for  the  com- 
plete transformation  of  the  slowly  decomposed  amido-phenol, 
and  this  again  brings  about  the  necessity  of  decomposing  the  ni- 
trogenous mercury  compounds  formed  in  the  solution  by  potas- 
sium sulfid,  which  is  added  after  or  with  the  soda-lye. 

325.  The  Dutch  Jodlbauer  Method. — The  Royal  Experiment 
Station  of  Holland  directs  that  the  jodlbauer  process  be  carried 
out  as  indicated  below.17 

The  reagents  necessary  are: 

1.  Phenolsulfuric  acid,  prepared  by  dissolving   100  grams  of 
pure  crystallized  phenol  in  pure  sulfuric  acid  (1.84)  and  making 
up  the  solution  to  a  liter  with  the  same  sulfuric  acid. 

2.  Zinc,  carefully  washed  and  thoroughly  dried. 

3.  Sodium  hydro.vid  solution,  the  same  as  is  used  in  the  kjeld- 
ahl  method. 

4.  Potassium  sulfid  solution,  made  by  dissolving  355  grams  of 
potassium  sulfid    (K2S),  or   sodium   sulfid  solution,  made  by  dis- 
solving 250  grams  of  sodium  sulfid  (Na,S)  in  a  liter  of  water. 

17  Methoden  van   Onderzoek    aan    de    Rijkslandbowproefstations  voor 
het  Jaar,  1894. 


3/6  AGRICULTURAL  ANALYSIS 

Oxidation  flasks  holding  about  200  cubic  centimeters,  and  dis- 
tillation flasks  holding  about  750  cubic  centimeters,  both  of  Bo- 
hemian glass  are  used. 

Manipulation. — Moisten  one  gram  of  substance  with  water,  dry 
and  introduce  into  an  oxidation  flask.  Cover  with  15  cubic  cen- 
timeters of  phenolsulfuric  acid  and,  after  cooling,  thoroughly  mix 
by  gently  shaking.  After  five  minutes  add  from  two  to  three 
grams  of  zinc  in  small  proportions,  keeping  the  flask  cool,  then  20 
cubic  centimeters  of  sulfuric  acid,  and  finally  two"  drops  of 
mercury.  Boil  the  mixture  till  the  fluid  is  colorless,  cool  and 
dilute.  Wash  into  a  distillation  flask  and  add  an  excess  of  sodium 
hydroxid  solution  and  25  cubic  centimeters  of  the  sodium  (or 
potassium)  sulfid  solution.  Distil  and  titrate  as  in  the  kjeldahl 
method. 

326.  The  Halle-Jodlbauer  Method.— At  the  Halle  Station  it  is 
the  uniform  practice  to  mix  the  nitrate  with  gypsum  before 
the  combustion.18  In  the  case  of  Chile  nitrates  10  grams 
are  rubbed  with  an  equal  amount  of  gypsum,  and  two  grams  of 
the  mixture,  equal  to  one  gram  of  the  nitrate,  used  for  the 
determination.  In  the  case  of  saltpeter  mixtures  which  contain 
over  eight  per  cent,  of  nitrogen,  one  gram  of  the  mixture  with 
gypsum  is  used,  of  guanos  one  and  a  half  grams,  and  of  lower 
forms  of  nitrates  or  mixtures  thereof,  from  three  to  five  grams. 

The  sample,  as  prepared  above,  is  treated  with  30  cubic  centi- 
meters of  a  mixture  of  phenolsulfuric  acid  and  phosphoric 
anhydrid.  The  mixture  is  prepared  by  dissolving  66  grams  of 
phenol  and  250  grams  of  phosphoric  anhydrid  in  strong  sulfuric 
acid,  and,  after  cooling,  mixing  the  two  solutions  and  making 
the  volume  up  to  1650  cubic  centimeters  with  pure  sulfuric  acid. 
The  mixture  contains,  in  30  cubic  centimeters,  one  and  two-tenths 
grams  of  phenol  and  four  grams  of  phosphoric  anhydrid.  In  the 
use  of  phenolsulfuric  acid  the  presence  of  phosphoric  anhydrid 
is  indispensable  in  keeping  the  sulfuric  acid  water-free  and  in 
absorbing  the  water  produced  by  the  combustion. 

18  Bieler  und  Schneidewind,   Die  agricultur-chemische  Versuchsstation 
Halle  a/S,  1892  :  34. 


USE;  OF  ZINC  SULFID  AND  SODIUM  THIOSULFATE          377 

The  phenolsulfuric  acid  used  contains  only  enough  phenol 
to  reduce  half  a  gram  of  saltpeter. 

The  sample  and  acid  mixture  having  been  put  in  the  combus- 
tion flask,  the  latter  is  heated  and  shaken,  at  intervals,  for  an 
hour  and  the  contents  cooled. 

The  conversion  of  the  nitrates  into  nitro-phenol  compounds  is 
finished  in  this  time,  and  the  next  step  consists  in  reducing  these 
bodies  to  the  amido-phenol  group.  This  is  accomplished  in  the 
cold  by  nascent  hydrogen  produced  by  the  addition  of  zinc  dust 
to  the  mixture.  From  one  to  three  grams  of  the  dust  are  to  be 
used  in  proportion  to  the  quantity  of  nitrates  originally  present. 

The  flask  should  be  placed  in  a  cooling  mixture  and  the  zinc 
dust  added  in  small  portions  to  prevent  a  too  violent  evolution 
of  hydrogen.  After  the  reduction  is  ended,  the  flask  is  allowed 
to  stand  for  two  hours,  after  which  the  combustion,  distillation, 
and  titration  are  accomplished  in  the  usual  way.  On  cooling, 
after  the  end  of  the  combustion,  the  contents  of  the  flask  become 
solid.  They  may  be  brought  again  into  the  liquid  state  by  shak- 
ing and  gentle  warming. 

327.  The  Salicylic  Acid  Method. — The  introduction  of  the  use 
of  salicylic  acid  as  the  proper   reagent  to  prevent -the  loss  of 
nitrogen  when  a  nitrate  :s  acted  on  by  sulfuric  acid  is  due  to 
Scovell.     It  was  noticed  that  the  action  of  phenol  was  too  violent 
to  protect  the  process  from  loss  of  nitrogen.     After  a  careful 
trial  of  many  organic  compounds  capable  of  forming,  nitro-com- 
pounds  in  those  circumstances,  salicylic  acid  was  selected  as  the 
most   promising  reagent.19   Rigid   trials   by    Scovell   and   others 
extending   over   many   years    have   confirmed   the   propriety    of 
this  choice.20     The  method  has  also  been  found  to  be  accurate 
in  the  presence  of  chlorids  as  well  as  of  nitrates. 

328.  Use    of    Zinc    Sulfid    and    Sodium    Thiosulfate. — During 
the    many    analyses    made    by    this    modified    method,    it  was 
noticed    that    on    pure    nitrates  there   was  apparently  a   slight 

19  Thesis  for  Degree  of  Doctor  of  Philosophy,    University  of  Illinois, 
June,  1906,  (Unpublished). 

10  Division  of  Chemistry,  Bulletin  16,  1887  :  51. 

Division  of  Chemistry,  Bulletin  19,  1888  :  47. 

New  Jersey  Agricultural  Experiment  Station  Report,  1887,  169. 


AGRICULTURAL  ANALYSIS 

loss  of  nitrogen  in  adding  the  zinc  dust.  This  was  also  a  tedious 
part  of  the  operation  as  the  zinc  dust  had  to  be  added  gradually. 
Finely  granulated  zinc  dust  was  tried,  but  in  such  cases  the  re- 
sults were  invariably  low.  The  results  were  lower  when  using 
chemically  pure  zinc  dust  instead  of  the  commercial  article.  An 
investigation  showed  that  the  commercial  zinc  dust  which  had 
hitherto  been  used  contained  some  zinc  sulfid.  This  suggested 
that  hydrogen  sulfid  might  complete  the  reduction  as  well  if  not 
better  than  nascent  hydrogen.  Working  on  this  theory,  Scovell 
and  Peter  made  a  series  of  experiments,  using  zinc  dust  in  one 
set  of  experiments  and  zinc  sulfid  in  another  set.21  The  results 
on  pure  potassium  nitrate,  containing  a  trace  of  water,  and 
13.83  per  cent,  of  nitrogen  were  as  follows: 

Average J3-76 

Theory l3-&3 

The  advantage  of  zinc  sulfid  over  zinc  dust  is :  First,  the 
liability  of  the  loss  of  nitrogen  is  not  so  great.  Second,  the 
zinc  sulfid  can  be  added  all  at  once,  and,  therefore,  it  is  less 
troublesome  and  more  rapid  than  when  the  zinc  dust  is  used. 
Third,  the  oxidation  is  more  rapid  and,  as  less  salts  are  present, 
the  distillation  is  more  quiet. 

In  1893  sodium  thiosulfate  was  substituted  for  zinc  sulfid  as 
the  reducing  agent  in  this  method,  not  because  better  results 
were  obtained,  but  because  it  was  found  to  be  difficult  to  get 
commercial  zinc  sulfid  free  from  ammonia.  The  comparative  re- 
sults obtained  by  the  different  chemists  using  these  two  reduc- 
ing agents  were  slightly  in  favor  of  zinc  sulfid.22 

Otto  Foerster  gives  the  following  as  the  reaction  when  sodium 
thiosulfate  is  used:23 

4HNO3+4H2SO4+Na2S2O3= 
4HO.NO2.SO2+2NaHSO4-f3H2O. 

But  it  would  be  interesting  to  know  whether  hydrogen  sulfid, 
which  is  also  formed  when  salicylic  acid  and  strong  sulfuric  acid 

11  Division  of  Chemistry,  Bulletin  24,  1890  :  91. 
**  Division  of  Chemistry,  Bulletin  38,  1893  :  34. 
u  Zeitschrift  fur  analytische  Chetnie,  1889,  28  :  422. 


THEORY  OF  THE  PROCESS  379 

and  nitrates  are  mixed,  does  not  play  at  least  a  part  in  the  re- 
duction of  the  nitro  into  the  amido  compounds. 

329.  Theory  of  the  Process. — The  theory  of  the  process  by 
which  salicylic  acid  converts  nitrates  to  ammonia  is  as  follows: 

r.  When  salicylic  acid  and  sulfuric  acid  are  added  to  a  nitrate, 
the  sulfuric  acid  takes  up  water  and  one  of  the  hydrogen  ele- 
ments of  the  salicylic  acid  is  replaced  by  NO2,  forming  nitro 
salicylic  acid.  This  reaction  takes  place  without  heat.  It  is 
probably  mononitro  and  not  dinitro  salicylic  acid  that  is  formed. 
The  reaction  is  probably  as  follows : 

(i)  C6HS.OH.CO2H+HNO8+H,SO4= 
C6H4(NO2).OH.CO2H+H,SO4+H2O. 

2.  Subsequently  when  zinc  sulfid  is  added  the  hydrogen  sulfid 
liberated  reduces  the  nitro  salicylic  acid  to  amido  salicylic  acid 
as  follows: 

(2)  C6H4(N02).OH.C02H+3H2S4-H2S04+ 
CcH4(NH2).OH.CO2H+3S+2H2O-f-H2SO4. 

3.  The  strong  sulfuric  acid  and  heat  on  the  amido  salicylic  acid 
breaks  it  up  and  there  is  formed  ammonium  sulfate,  carbonic 
acid,  sulfur  dioxid  and  water,  as  follows : 

(3)  2C6H4(NH2).OH.CO2H+28H2SO4= 
( NH4)  2SO4+  i4CO2+27SO,+32H,O. 

Similar  reaction  probably  occurs  when  benzoic  acid  or  phenol 
is  used,  but  either  nitro  compounds  are  not  as  readily  formed  or 
they  are  not  as  easily  converted  into  amido  compounds,  and  pro- 
bably the  heat  caused  by  the  reaction  when  phenol  is  used  is  the 
cause  of  the  loss  of  some  nitric  acid.  Furthermore,  phenol  and 
benzoic  acid  do  not  break  up  as  easily  in  the  final  reaction  and, 
therefore,  it  takes  longer  to  complete  the  oxidation  than  when 
salicylic  acid  is  used. 

Other  nitro-  and  amido-forming  compounds  might  be  sub- 
stituted for  salicylic  acid,  but  by  the  use  of  salicylic  acid,  the 
method  is  so  simple  and  accurate  that  it  is  doubtful  whether  any 
substance  other  than  salicylic  acid  would  improve  the  method. 

Other  substances  have  been  under  observation,  e>  g.,  pure  potas- 
sium nitrate,  using  gallic  acid  in  the  place  of  salicylic  acid,  gave 


380  AGRICULTURAL  ANALYSIS 

6.68  per  cent,  of  nitrogen ;  pyrogallic  acid,  8.21  per  cent. ;  phenol, 
13.62  per  cent;  benzaldehyde,  13.62  per  cent.;  phenyl  salicylate, 
13.72  per  cent.  It  is  interesting  to  note  that  phenyl  salicylate 
gave  satisfactory  results ;  the  oxidation,  however,  is  not  as  rapid 
as  when  salicylic  acid  is  used. 

For  ease  in  manipulation,  rapidity  of  work,  and  accuracy  of 
results  the  salicylic  acid  method  is  to  be  recommended. 

330.  The  Official  Kjeldahl  Method  for  Nitric  Nitrogen. — As 
has  already  been  stated,  the  presence  of  certain  organic  com- 
pounds rich  in  hydrocarbons  permits  the  reduction  of  nitric 
nitrogen  to  ammonia  by  combustion  with  sulfuric  acid.  Benzol, 
phenol,  and  salicylic  acid  have  all  been  used  for  this  purpose. 
The  official  chemists  have  adopted  for  their  method  the  sali- 
cylic acid  process  first  proposed  by  Scovell.24 

Besides  the  reagents  and  apparatus  given  under  the  kjeldahl 
method  there  will  be  needed: 

1 i )  Zinc  dust :     This  should  be  an  impalpable  powder ;  granu- 
lated zinc  or  zinc  filings  will  not  answer. 

(2)  Sodium  thiosulfate. 

(3)  Commercial  salicylic  acid. 

It  is  found  most  convenient  to  prepare  a  solution  of  33.3  grams 
of  salicylic  acid  in  one  liter  of  the  strongest  sulfuric  acid,  and 
keep  it  for  use  rather  than  to  mix  it  for  each  combustion. 

The  Manipulation. — Place  from  seven-tenths  to  three  and  five- 
tenths  grams  of  the  substance  to  be  analyzed  in  a  kjeldahl  di- 
gesting flask,  add  30  cubic  centimeters  of  sulfuric  acid  containing 
one  gram  of  salicylic  acid,  and  shake  until  thoroughly 
mixed,  then  add  five  grams  of  crystallized  sodium  thiosulfate ; 
or  add  to  the  substance  30  cubic  centimeters  of  sulfuric  acid 
containing  two  grams  of  salicylic  acid,  then  add  gradually  two 
grams  of  zinc  dust,  shaking  the  contents  of  the  flask  at  the  same 
time.  Finally  place  the  flask  on  the  stand  for  holding  the  diges- 
tion flasks,  where  it  is  heated  over  a  low  flame  until  all  danger 
from  frothing  has  passed.  The  heat  is  then  raised  until  the 
acid  boils  briskly  and  the  boiling  continued  until  white  fumes 
no  longer  escape  from  the  flask.  This  requires  about  five  or  10 
14  Division  of  Chemistry,  Bulletin  16,  1887  :  51. 


GUNNING   METHOD   FOR   NITRIC    ACID  381 

minutes.  Add  now  approximately  0.7  gram  of  mercuric  oxid 
or  its  equivalent  in  metallic  mercury,  and  continue  the  boiling 
until  the  liquid  in  the  flask  is  colorless  or  nearly  so.  In  case  the 
contents  of  the  flask  are  likely  to  become  solid  before  this  point 
is  reached,  add  10  cubic  centimeters  more  of  sulfuric  acid.  Com- 
plete the  oxidation  with  a  little  potassium  permanganate  in  the 
usual  way,  and  proceed  with  the  distillation  as  described  in  the 
kjeldahl  method.  The  reagents  should  be  tested  by  blank  experi- 
ments. The  object  of  adding  the  sodium  thiosulfate  is  to  prevent 
the  development  of  the  amido-mercurous  salts  which  require  to 
"be  subsequently  broken  up  by  the  addition  of  a  sulfid.  The  reac- 
tion which  takes  place  is  represented  by  the  following  formula : 

/NH>\ 

Hg<  >SO4  +  Na,S,O3-5H2O  ==  HgS  +  (NH4)2SO4+  Na,SO4 

\NH/ 

-f-4H,O.  The  sodium  thiosulfate  may  also  be  added  after  the 
•digestion  instead  of  the  sodium  sulfid.25 

331.  Gunning  Method  for  Nitric  Acid. — The  essential  features 
of  this  modification  are  due  to  Winton  and  Voorhees.26 
The  modifications  of  the  kjeldahl  method,  for  similar  purposes, 
furnished  the  material  details  for  the  gunning  modified  process. 
Winton  reports  good  results  from  digesting  for  two  hours  from 
half  a  gram  to  a  gram  of  the  sample  with  30  cubic  centimeters 
of  sulfuric  containing  two  grams  of  salicylic  acid,  in  a  flask  of 
half  a  liter  capacity.  Two  grams  of  zinc  dust  are  then  slowly 
added,  with  constant  shaking,  and  the  flask  heated,  at  first  gently, 
until,  after  boiling  a  few  minutes,  dense  fumes  are  no  longer 
•emitted.  Three  grams  of  potassium  sulfate  are  next  added  and 
the  boiling  continued  until  the  solution  is  colorless,  or,  if  iron  be 
present,  until  a  light  straw  color  is  produced.  On  cooling,  when 
the  mixture  begins  to  solidify,  water  is  added  with  caution,  and 
afterwards  sodium  hydroxid,  and  the  ammonia  is  obtained  by 
•distillation. 

In  the  process,  as  conducted  by  Voorhees,  about  one  gram  of 

25  Neuberg,  Beitrage  zur  chemischen  Physiologic  und  Pathologic,  1902, 
2  :  214. 

26  Connecticut  Agricultural  Experiment  Station,  Bulletin  112,  1892  :  3. 
Division  of  Chemistry,  Bulletin  35,  1892  :  86. 


32  AGRICULTURAL   ANALYSIS 

the  sample  is  digested  with  10  grams  of  potassium  sulfate  and 
30  cubic  centimeters  of  sulfuric  containing  one  gram  of  salicylic 
acid,  and  three  grams  of  zinc  sulfid.  The  heat  is  kept  down  until 
frothing  ceases,  and  then  the  mass  kept  in  gentle  ebullition  until 
clear.  The  distillation  is  accomplished  with  the  usual  precau- 
tions. The  voorhees  process  is  superior  to  that  recommended 
by  Winton  in  adding  the  potassium  sulfate  at  the  beginning  of 
the  combustion. 

332.  Official  Gunning  Method  Modified  to  Include  the  Nitro- 
gen of  Nitrates.27 — In  a  digestion  flask  holding  from  250  to  500 
cubic  centimeters  place  from  0.7  to  3.5  grams  of  the  substance 
to  be  analyzed,  according  to  the  amount  of  nitrogen  present. 
Add  from  30  to  35  cubic  centimeters  of  salicylic  acid  mixture; 
namely,  30  cubic  centimeters  of  sulfuric  to  one  gram  of  salicylic 
acid,  shake  until  thoroughly  mixed,  and  allow  to  stand  from  five 
tc   10  minutes,  with  frequent  shaking;  then  add  five  grams  of 
sodium  thiosulfate  and  TO  grams  of  potassium  sulfate.      (It  is 
suggested  that  after  adding  the  sodium  thiosulfate,  the  solution 
be  heated   for   five  minutes,  cooled   and   the   potassium   sulfate 
added.     This  variation  prevents   foaming).     Heat   very  gently 
until  frothing  ceases,  then  strongly  until  nearly  colorless.    Dilute,, 
neutralize,  and  distil  as  in  the  gunning  method. 

DETERMINATION  OF  NITROGEN  IN  DEFINITE  FORMS    OF 

COMBINATION 

333.  Introductory  Considerations. — In     the     foregoing    pages 
has  been  given  a  summary  of  the  methods  most  in  vogue  for  the 
estimation  of  nitrogen    in    fertilizers    and    fertilizing    materials. 
There  are  many  cases  in  which  the  analyst  may  have  to  deal 
with  a  definite  chemical   compound,   and   where  a  modified   or 
shorter  method  may  be  used.     There  are  other  cases  in  which 
the  nitrogen  may  be  present  in  two  or  three  definite  forms,  as  in 
artificially  mixed  fertilizers,  and  where  it  is  desirable  to  show 
the  proportions  in  which  the  various   forms  are  present.     For 
these  reasons  it  is  necessary  to  be  able  to  use  methods  by  which 
the  percentage  of  nitrogen  in  its  various  forms  may  be  relatively,. 

n  Bureau  of  Chemistry,  Bulletin  107,  1907  :  8. 


DETERMINATION  OF  AMMONIA  383 

as  well  as  absolutely,  determined.  Such  a  case  would  be  presented 
for  instance,  in  that  of  a  fertilizer  containing  dried  blood,  sodium 
nitrate,  and  ammonium  sulfate.  It  is  evident  here  that  the  total 
nitrogen  could  be  determined  by  the  volumetric  method  by  com- 
bustion with  copper  oxid,  or  by  the  moist  combustion  process 
adapted  to  nitric  nitrogen,  but  the  method  of  determining  the 
percentage  of  each  constituent  has  not  yet  been  described. 

We  have  to  deal  here  with  a  case  entirely  similar  to  that  of 
phosphoric  acid  in  a  superphosphate.  There  is  no  doubt  what- 
ever of  the  uneven  assimilability  of  the  different  forms  of  nitro- 
gen. A  nitrate,  for  instance,  is  already  in  condition  for  assimi- 
lation by  plants.  An  ammoniacal  salt  is  only  partly  changed  to 
a  state  suited  to  plant  nutrition,  while  organic  nitrogen  is  forced 
to  undergo  a  complete  transformation  before  it  becomes  available 
to  supply  the  needs  of  the  growing  plant.  It  is  important,  there- 
fore, equally  to  the  analyst,  the  merchant  and  the  agronomist, 
to  know  definitely  the  forms  of  combination  in  which  the  nitrogen 
exists  and  the  relative  proportion  of  the  different  combinations. 

334.  Nitrogen  as  Ammonia. — The     most     frequent     form     in 
which  nitrogen  as  ammonia  is  used  for  fertilizing  is  as  sulfate. 
The  method  of  determination  to  be  described  is,  however,  equally 
applicable  to  all  ammonia  salts.     When  no  other  form  of  nitrog- 
enous compound  is  present  the  ammonia  can  be  easily  and  di- 
rectly determined  by  distillation  with  soda-  or  potash-lye,  as  de- 
scribed in  the  final  part  of  the  moist  combustion  process. 

335.  Determination  of  Ammonia. — To   one  gram  of  the  am- 
monia salt  add  from  200  to  300  cubic  centimeters  of  water  and 
30  grams  of  the  soda-lye  used  in  the  moist  combustion  process ; 
distil,  collect  the  ammonia,  and  titrate  the  excess  of  sulfuric  acid 
exactly  as  there  described. 

Fresenius  recommends  that  the  ammonia  expelled  by  distilla- 
tion be  taken  up  by  a  standard  solution  of  sulfuric  (hydrochloric, 
oxalic)  acid,  the  excess  of  which  is  titrated  with  a  standard  solu- 
tion of  soda  or  other  alkali,  using  litmus  as  an  indicator.28  If  the 
distillate,  on  examination,  be  found  to  contain  thiocyanate,  soda- 
M  Chemical  Quantitative  Analysis,  Cohn's  Translation,  from  the 
Revised  6th  German  Edition,  1904,  1  :  254. 


AGRICULTURAL   ANALYSIS 

lye  can  not  be  used  for  the  expulsion  of  ammonia,  but  in  its  place 
caustic  magnesia  is  applied. 

In  all  cases  where  organic  matter  containing  nitrogen  is  pres- 
ent, caustic  magnesia  must  be  substituted  for  the  soda  solution. 
The  magnesia  must  be  added  in  sufficient  excess  and  the  distil- 
lation continued  a  little  longer  than  is  necessary  when  soda-lye 
is  used.  Otherwise  the  details  of  the  operation  are  the  same. 

In  a  mixed  fertilizer  containing  organic  nitrogen  and  ammo- 
nia salts,  the  total  nitrogen  can  be  determined  by  the  moist  com- 
bustion process,  and  the  ammoniacal  nitrogen  by  distillation  with 
magnesia.  The  difference  between  the  two  results  will  give  the 
nitrogen  due  to  the  organic  matter. 

To  avoid  any  danger  whatever  of  decomposing  organic  nitrog- 
enous compounds,  the  ammonia  may  be  determined  in  the  cold 
by  treatment  with  soda-lye,  under  a  bell- jar  containing  some  set 
sulfuric  acid.  The  operation  must  be  allowed  to  continue  for 
many  days.  Even  at  the  end  of  a  long  time  it  will  be  found  that 
some  ammonia  is  still  escaping.  It  may,  therefore,  be  finally  in- 
ferred that  all  the  nitrogen  as  ammonia  is  not  obtained  by  this 
process,  or  that  even  magnesia  may  gradually  convert  other 
nitrogenous  compounds  into  ammonia.  In  this  connection  the 
methods  of  determining  ammonia  in  soils  in  paragraphs  450,  451 
and  452,  Volume  I,  may  be  consulted. 

336.  Method  of  Boussingault. — The  official  French  method 
is  essentially  the  original  method  of  Boussingault  with  slight 
modifications.  It  is  conducted  as  follows  :29  In  case  the  sam- 
ple is  ammonium  sulfate,  about  half  a  gram  is  placed  in  a  flask 
of  half  a  liter  capacity,  together  with  300  cubic  centimeters  of 
distilled  water  and  two  grams  of  caustic  magnesia.  The  flask 
is  connected  with  a  condenser  of  glass  or  metal  which  ends  in  a 
tube  drawn  out  to  a  point  and  dipping  beneath  the  set  acid  in 
the  receiver  in  the  usual  way.  The  acid  is  colored  with  litmus 
or  lacmoid  tincture.  The  distillation  is  continued  until  about 
loo  cubic  centimeters  have  gone  over.  The  receiver  is  then  re- 
.moved  with  the  usual  precautions  and  the  residual  acid  titrated. 
Suppose  20  cubic  centimeters  of  normal  acid  have  been  employed" 
19  Guide  pour  le  Dosage  de  1*  Azote  :  14. 


DETERMINATION  OF  THIOCYANATES  385 

and  \2.y2  cubic  centimeters  of  normal  alkali  be  necessary  to  neu- 
tralize the  excess  of  the  acid.  Then  the  nitrogen  is  found  by 
the  following  equations:  20.0 — 12.5=7.5  an<^  7.5X0.014=0.105 
gram  =  weight  of  nitrogen  found.  Then  0.105X100-^-0. 5=21 
=per  cent,  of  nitrogen  found. 

The  distilling  apparatus  of  Aubin  is  preferred  by  the  French 
chemists,  an  apparatus  so  arranged  with  a  reflux  partial  con- 
denser that  nearly  all  the  aqueous  vapor  is  returned  in  a  con- 
densed state  to  the  flask,  while  the  ammonia,  on  account  of  its 
great  volatility,  is  carried  over  into  the  receiver.  To  avoid  the 
regurgitation  which  might  be  caused  by  the  concentrated  ammo- 
nia gas  coming  in  contact  with  the  acid,  the  separable  part  of  the 
condensing  tube  is  expanded  into  a  bulb  large  enough  to  hold 
all  the  acid  which  lies  above  its  mouth.  By  means  of  this  appara- 
tus the  ammonia  is  all  collected  in  the  standard  acid  without 
greatly  increasing  its  volume  and  the  titration  is  thus  rendered 
sharper.  The  employment  of  caustic  magnesia  has  the  advan- 
tage of  not  decomposing  any  organic  matters  or  cyanids  that  may 
be  present. 

If  the  sample  under  examination  hold  part  of  its  ammonia  a^ 
ammonium  magnesium  phosphate,  it  will  be  necessary  first  to 
treat  it  with  sulfuric  acid  in  order  to  set  the  ammonia  free,  and 
then  to  use  enough  of  the  magnesium  oxid  to  neutralize  the  ex- 
cess of  the  sulfuric  acid  and  still  supply  the  two  grams  necessary 
for  the  distillation.  When  the  sample  contains  a  considerable 
quantity  of  organic  matter  it  sometimes  tends  to  become  frothy 
towards  the  end  of  the  distillation.  This  trouble  can  be  avoided 
by  introducing  into  the  flask  one  or  two  grams  of  paraffin. 

Where  carbon  dioxid  is  given  off  during  the  distillation,  the 
contents  of  the  receiver  must  be  boiled  before  titration,  or  else 
lacmoid  must  be  used  as  an  indicator  instead  of  litmus. 

337.  Determination  of  Thiocyanates  in  Ammoniacal  Fertilizers. 
— The  extended  use  of  ammonium  sulfate  as  a  fertilizer 
renders  it  important  to  determine  the  actual  constituents  which 
may  be  present  in  samples  of  this  material.  The  following  bodies 
have  been  found  in  commercial  ammonium  sul fates :  Sulfuric 
acid,  chlorin,  ammonia,  thiocyanic  acid,  potash,  soda,  lime  and 
'3 


386  AGRICULTURAL  ANALYSIS 

iron  oxid.  These  are  found  in  the  soluble  portions.  In  the  in- 
soluble portions  have  been  found  silica,  sulfates,  lime,  magnesia 
and  iron  oxid.  A  sample  of  commercial  ammonium  sulfate  ana- 
lyzed by  Jumeau  contained  the  following  substances:30 

Per  Cent. 

Moisture 10.5109 

Ammonium  sulfate 67.8453 

Ammonium  thiocyanate ...  9-3935 

Sodium  sulfate 9.2429 

Potassium  sulfate 0.9774 

Calcium  sulfate 0.6800 

Iron  thiocyanate 0.5000 

Magnesium  chlorid traces 

Silica 0.0830 

Undetermined 0.7670 

The  determination  of  the  thiocyanic  acid  in  the  thiocyanate 
is  generally  made  by  the  oxidation  of  the  sulfur  to  sulfuric  acid 
and  its  subsequent  weighing  in  the  form  of  barium  sulfate. 
Jumeau  has  modified  the  method  by  determining  the  amount  of 
the  thiocyanate  by  means  of  a  titrated  liquid.  The  method  is 
practiced  as  follows: 

A  solution  of  ammonium  thiocyanate  is  prepared,  containing 
eight  grams  of  this  salt  per  liter,  and  its  exact  content  of  thio- 
cyanate is  rigorously  determined  by  titration  with  silver  nitrate 
or  by  the  weight  of  the  barium  sulfate  produced  after  the  oxida- 
tion of  the  sulfur.  Ten  cubic  centimeters  of  the  titrated  liquor 
are  diluted  with  water  to  about  100  cubic  centimeters  and  10 
cubic  centimeters  of  pure  sulfuric  acid  added.  Afterward,  drop 
by  drop,  a  solution  of  potassium  permanganate  is  added,  con- 
taining about  10  grams  of  that  salt  per  liter.  The  perman- 
ganate is  instantly  decolorized.  There  is  an  evolution  of  hydro- 
cyanic acid  as  the  thiocyanate  passes  to  the  state  of  sulfuric  acid. 
A  single  drop  in  excess  gives  to  the  mixture  the  well-known  rose 
coloration  of  the  permanganate  solution  which  persists  for  sev- 
eral hours.  The  number  of  cubic  centimeters  necessary  to  pro- 
duce the  persistent  rose  tint  is  noted  and  the  same  operation  is 
carried  on  with  from  one-half  to  one  gram  of  the  unknown  prod- 
uct which  is  to  be  assayed.  A  simple  proportion  indicates  the 
80  Revue  de  Chimie  analytique  applique'e,  1893,  1:51. 


SEPARATION    OF    PROTEID  387 

content  of  the  thiocyanate  in  the  unknown  body.  The  process 
is  of  great  exactitude  and  permits  the  rapid  determination  of 
thiocyanic  acid  in  the  presence  of  chlorids,  cyanids,  etc.,  which 
remain  without  action  upon  the  permanganate.  In  case  chlorids 
and  cyanids  are  absent  the  thiocyanate  can  be  determined  directly 
by  silver  nitrate  either  by  weighing  the  precipitate  or  by  the  pro- 
cess of  Volhardt,  based  upon  the  precipitation  of  the  silver  by 
thiocyanate  in  the  presence  of  a  ferric  salt.  The  end  of  the 
reaction  is  indicated  by  the  red  coloration  which  the  liquid  shows 
when  the  thiocyanate  is  in  excess. 

338.  Separation  of  Proteid  from  Amid  and  Other  Forms  of 
Nitrogen  in  Organic  Fertilizers. — It  may  be  of  interest  to  the 
dealer,  farmer,  and  analyst  to  discriminate  between  the  proteid 
and  other  nitrogen  in  fertilizers,  such  as  oil-cakes,  etc.  The  final 
value  of  the  nitrogen  for  plant  nourishment  is  not  greatly  dif- 
ferent, but  the  immediate  availability  for  the  use  of  plants  is  a 
matter  of  some  importance.  The  most  convenient  process  in  such 
a  case  is  the  copper  hydroxid  separation  process  as  improved  by 
Stutzer.31  The  process  is  conveniently  carried  out  in  accordance 
with  the  method  prescribed  by  the  official  chemists.32 

Total  Crude  Protein. — Determine  nitrogen  as  directed  for  nitro- 
gen in  fertilizers  and  multiply  the  result  by  6.25  for  the  crude 
protein. 

Determination  "of  Albuminoid  Nitrogen. — To  0.7  gram  of  the 
substance  in  a  beaker  add  100  cubic  centimeters  of  water,  heat 
to  boiling,  or,  in  the  case  of  substances  rich  in  starch,  heat  on 
the  water  bath  10  minutes,  and  add  a  quantity  of  cupric  hydroxid 
mixture  containing  one-half  gram  of  the  hydroxid;  stir  thor- 
oughly, filter  when  cold,  wash  with  cold  water,  and  put  the  filter 
and  its  contents  into  the  flask  containing  the  concentrated  sulfuric 
acid  for  the  determination  of  nitrogen.  The  filter  papers  used 
must  be  practically  free  of  nitrogen.  Add  sufficient  potassium 
sulfid  solution  to  completely  precipitate  all  copper  and  mercury, 
and  proceed  as  in  the  moist  combustion  process  for  nitrogen.  If 

31  Journal  fiir  Landwirtschaft,  1880,  28  :  103. 

Chemiker-Zeitung,   1880,  4  :  360. 
™  Bureau  of  Chemistry,  Bulletin  107,  1907  :  38. 


388  AGRICULTURAL  ANALYSIS 

the  substance  examined  consists  of  seed  of  any  kind,  or  residues 
of  seeds,  such  as  oil-cake  or  anything  else  rich  in  alkaline  phos- 
phates, add  a  few  cubic  centimeters  of  a  concentrated  solution 
of  alum  free  from  ammonia  just  before  adding  the  cupric  hy- 
droxid,  and  mix  well  by  stirring.  This  serves  to  decompose  the 
alkaline  phosphates.  If  this  be  not  done,  cupric  phosphate  and 
free  alkali  may  be  formed,  and  the  protein-copper  precipitate 
may  be  partially  dissolved  in  the  alkaline  liquid. 

Cupric  Hydro.vid. — Prepare  the  cupric  hydroxid  as  follows: 
Dissolve  100  grams  of  pure  cupric  sulfate  in  five  liters  of  water, 
and  add  2.5  cubic  centimeters  of  glycerol ;  add  a  dilute  solution 
of  sodium  hydroxid  until  the  liquid  is  alkaline ;  filter,  rub  the 
precipitate  up  with  water  containing  five  cubic  centimeters  of 
glycerol  per  liter,  and  wash  by  decantation  or  filtration  until  the 
washings  are  no  longer  alkaline.  Rub  the  precipitate  up  again  in 
a  mortar  with  water  containing  10  per  cent,  of  glycerol,  thus 
preparing  a  uniform  gelatinous  mass  that  can  be  measured  out 
with  a  pipette.  Determine  the  quantity  of  cupric  hydrate  per 
cubic  centimeter  of  this  mixture. 

Amid  Nitrogen. — The  albuminoid  nitrogen  determined  as  above 
subtracted  from  the  total  gives  that  part  of  the  organic  nitrogen 
existing  in  the  sample  as  amids  and  in  other  allied  forms. 

339.  Separation  of  Nitric  and  Ammoniacal  from  Organic  Nitro- 
gen.— The  nitrogen  being  present  in  three  for/ns,  viz.,  organic, 
ammoniacal  and  nitric,  the  separation  of  the  latter  two  may  be  ac- 
complished by  the  following  procedure  :3:!  One  gram  of  the  fer- 
tilizer is  exhausted  on  a  small  filter  with  a  two  per  cent,  solu- 
tion of  tannin,  using  from  30  to  40  cubic  centimeters  in  small 
portions.  This  is  sufficient  to  dissolve  all  the  nitrates  and  the 
greater  portion  of  the  ammoniacal  salts,  while  the  tannin  ren- 
ders insoluble  all  the  organic  nitrogenous  compounds.  The  filter 
and  its  contents  are  treated  for  nitrogen  by  the  kjeldahl  process. 
When  the  distillation  and  titration  are  completed  the  solution 
obtained  by  the  aqueous  tannin  is  added  to  the  distilling  flask 
and  the  operation  continued.  This  represents  the  ammoniacal 
nitrogen. 

3S  Aubin  et  Quenot,  Bulletin  de  la  Soci£t£  chimique  de  Paris,  1890,  [3], 
3  :  324- 


METHOD  OF  DETERMINING  NITROGEN  389 

The  nitric  acid  is  estimated  by  the  ferrous  iron  or  other  appro- 
priate method,  to  be  described  further  on,  in  another  portion  of 
the  substance. 

340.  Method  of  French  Commission  for  Determining  Nitrogen. 
— Several   methods   are   proposed   by   this   commission    for  the 
determination  of  nitrogen.34     The  old  method  of  combustion  with 
soda-lime  which  is  conducted  according  to  the  general  principles 
is  described  in  full.  When  the  nitrogen  is  to  be  determined  in  sub- 
stances which  are  not  homogeneous  and  which  it  is  difficult  to 
reduce  to  a  powdered  state,  a  modification  of  the  process,  due  to 
Grandeau,  is  employed.     Such  substances  are,  for  instance,  pieces 
of  cloth,  leather,  wool,  horns  and  hair.     It  is  almost  impossible 
to  obtain  a  homogeneous  mixture  of  such  bodies.     Large  quan- 
tities of  them  are,  therefore,  according  to  this  method,  treated 
with  sulfuric  acid  and  then  heated  until  the  decomposition  is 
complete  and  they  are  easily  reduced  to  a  homogeneous  mass. 
This  is  best  secured  by  adding  some  finely  powdered  gypsum. 
When  the  decomposition  is  completed  and  a  homogeneous  mass 
is  secured,  the  rest  of  the  process  is  conducted  by  the  usual 
methods. 

The  French  commission  also  recommends  the  common  method 
already  described  for  the  determination  of  nitrogen  in  an  organic 
state  by  the  process  of  Kjeldahl,  and  of  nitrogen  in  the  nitric 
state  and  of  sulfate  of  ammonium  by  the  methods  usually  em- 
ployed. 

341.  Method  of  Determining  Nitrogen  Adopted  by  the  Union  of 
German  Fertilizer  Manufacturers. — Nitric  Nitrogen. — The  nitro- 
gen in  the  form  of  nitrates  is  determined  by  the  method  of  Ulsch 
and  Devarda.35 

Ammoniacal  Nitrogen. — This  is  determined  in  the  usual  way 
by  titration  with  an  alkali.  Freshly  burned  magnesia  hydrate  is 
employed  as  an  alkaline  reagent,  although  lime  may  also  be 
used  where  little  or  no  organic  matter  is  present,  and  the  am- 
monia is  mostly  in  the  form  of  ammoniacal  salt.  Soda-lye  should 
84  Grandeau,  Traite"  d'Analyse  des  Matures  agricoles,  3d  Edition,  1897, 

1  ;  427- 

K  Methoden  zur  Untersuchung  der  Kunstdiingeniittel,  1903  :  15. 


39°  AGRICULTURAL  ANALYSIS 

only  be  used  when  it  is  certain  that  no  organic  nitrogen  is  present. 
The  ammonia  is  collected  in  set  sulfuric  acid,  and,  as  an  indicator, 
it  is  recommended  to  use  paranitro-phenol  solution  in  the  pro- 
portion of  one  to  10  of  alcohol.  Tincture  of  cochineal  or  congo 
red  in  water  is  also  permitted. 

Organic  Nitrogen. — The  method  of  Kjeldahl,  with  its  modern 
modification  for  the  inclusion  of  nitric  nitrogen,  is  recommended. 

342.  Estimation  of  Perchlorate  in  Chile  Saltpeter. — Attention 
is  called  to  the  occasional  occurrence  in  Chile  saltpeter  of 
potassium  perchlorate.  The  method  employed  depends  upon  the 
determination  of  the  chlorin  content  of  the  material  under  inves- 
tigation both  before  and  after  the  decomposition  of  the  perchlo- 
rate. The  conversion  of  perchlorate  of  potassium  is  secured  by 
simple  ignition  or  by  ignition  after  the  addition  of  different  re- 
agents, as,  for  instance,  metallic  lead,  caustic  lime,  sodium  car- 
bonate, magnesium  oxid,  etc.  The  following  method  is  recom- 
mended as  satisfactory  and  easily  carried  out.36 

In  this  method  five  grams  of  Chile  saltpeter,  in  which  the 
amount  of  chlorin  has  been  determined,  is  placed  in  a  porcelain 
crucible  of  about  40  to  50  cubic  centimeters  capacity  with  from 
15  to  20  grams  of  lead  borings  and  submitted  to  a  gradually  in- 
creased heat.  When  the  salt  and  the  lead  are  melted,  the  mass 
is  vigorously  stirred  with  a  copper  wire  with  a  regulation  of  the 
heat  so  as  not  to  secure  a  too  rapid  evaporation  of  the  mass. 
When  the  mass  begins  to  thicken  and  only  a  few  bubbles  of  gas 
are  escaping,  the  heat  is  raised  to  a  dark  red  on  the  bottom  of 
the  crucible  and  held  at  this  temperature  for  one  or  two  minutes. 
After  cooling,  the  melt,  which  now  contains  nitrate  and  chlorate, 
is  softened  with  hot  water  and  washed  into  a  beaker.  Three  or 
four  grams  of  carbonate  of  soda  are  added  and  the  mixture 
gradually  warmed.  After  filtration  nitric  acid  is  added  to  the 
filtrate  to  acidity,  and  the  chlorin  estimated  in  the  usual  way  with 
the  nitrate  of  silver. 

From  the  amount  of  chlorin  obtained,  that  which  was  originally 
present  is  subtracted  and  the  difference  is  the  chlorin  due  to 
*  Selckmann,  Zeitschrift  fur  angewandte  Chemie,  1898,  11  :  101. 


METHOD  OF  SCHLOESING  391 

perchlorate.    One  equivalent  of  silver  nitrate  corresponds  to  one 
equivalent  of  potassium  perchlorate. 

343.  Method  of  Blattner-Brasseur/-7— In  this  method  five  grams 
of    saltpeter,    which    has    been    freed    from    moisture  by  heat- 
ing to   150°,  are  treated  with  from  seven  to  eight  grams  of 
pure   chlorin-free  calcium  hydrate   in   a   porcelain  or  platinum 
crucible  of  about  25  to  30  cubic  centimeters  capacity  and  the 
covered  crucible  heated  for  15  minutes  over  a  bunsen.     The  ig- 
nited mass  is  dissolved  and  neutralized  with  nitric  acid  and  the 
chlorin  titrated  with  nitrate  of  silver  or  estimated  by  the  gravi- 
metric method  as  above  described. 

THE  NITRIC  ACID  PROCESS 

344.  Occurrence  of  Highly  Oxidized  Nitrogen. — The  nitrogen 
of  fertilizers,  soil  waters,  etc.,  often  exists  in  a  highly  oxidized 
state  as  nitrous  or  nitric  acid  or  compounds  thereof.     The  fol- 
lowing paragraphs  are  devoted  to  the  description  of  methods 
employed  for  estimating  nitrogen  in  these  states  of  combination 
and  the  principles  on  which  they  are  based.     The  processes  for 
estimating   nitrogen  by   combustion   with   copper   oxid   and  by 
moist  combustion  with  sulfuric  acid  have  both  been  used  for  the 
determination  of  the  quantity  of  nitrogen  existing  in  a  highly 
oxidized  state.     These  processes  have  been  fully  discussed  under 
their  proper  heads.    In  the  case  of  soil  extracts,  drainage  waters, 
etc.,  it  will  be  sufficient  to  discuss,  for  the  present,  only  those  pro- 
cesses adapted  especially  to  a  quick  and  accurate  estimation  of 
oxidized  nitrogen  when  occurring  in  relatively  small  quantities. 

345.  Method  of  Schloesing. — The  principle  of  the  method  of 
Schloesing  depends  on  the  decomposition  of  nitrates  in  the  pres- 
ence of  a  ferrous  salt  and  a  strong  mineral  acid.38     The  nitrogen 
in  the  process  appears  as  nitric  oxid,  the  volume  of  which  may 
be  directly  measured,  or  it  may  be  converted  into  nitric  acid  and 
titrated  by  an  alkali. 

87  Chemiker-Zeitung,  1900,  24  :  767. 

38  Annales  de  Chimie  et  de  Physique,  1854,  [3],  40  :  479- 

Zeitschrift  fur  analytische  C'hemie,  1870,  9  :  24. 

Die  landwirtscbaftlichen  Versuchs-Stationen,  1869,  12  :  164. 

Journal  of  the  Chemical  Society,  1880,  37  1468;  1882,  41  :  345;   1889, 
55  :  537- 


392 


AGRICULTURAL  ANALYSIS 


The  typical  reactions  which  take  place  are  represented  in  the 
following  equation : 

6FeCl2+2KNO3+8HCl=3Fe2Cl6+2KCl+4H2O+2NO. 
346.  Schloesing's  Modified  Method. — The  schloesing  method 
as  now  practiced  by  the  French  chemists  is  conducted  in  the  ap- 
paratus shown  in  Fig.  20. 39  The  carbon  dioxid  is  generated  by 
the  action  of  the  hydrochloric  acid  in  F  on  the  fragments  of 
marble  in  A.  After  passing  the  wash-bottle,  the  gas  enters  the 
small  tubulated  retort,  C,  which  contains  the  nitrate  in  solution. 
When  the  quantity  of  nitrate  is  small,  as  in  ordinary  soils,  100 
grams  are  placed  in  an  extraction  flask,  plugged  with  cotton,  and 


Fig.  20.     Schloesing's  Apparatus  for  Nitric  Acid. 

a  layer  of  the  same  material  is  placed  over  the  soil  for  the  pur- 
pose of  securing  an  even  distribution  of  the  extracting  liquid. 
This  liquid  is  distilled  water  containing  in  each  liter  one  gram 
of  calcium  chlorid.  The  purpose  of  using  the  calcium  chlorid  is 
tc  prevent  the  soil  from  becoming  compacted,  which  would  ren- 
der the  extraction  of  the  nitrate  difficult.  The  extracting  liquid 
is  allowed  to  fall,  drop  by  drop,  from  a  mariotte  bottle  until  the 
filtrate  amounts  to  500  cubic  centimeters.  This  volume*  is  con- 
centrated on  a  sand-bath  until  it  is  reduced  to  10  or  15  cubic  cen- 
timeters, when  it  is  transferred  to  a  flat-bottomed  dish  and  the 
evaporation  finished  over  steam,  care  being  taken  not  to  allow 
the  temperature  to  exceed  100°. 

39  Encyclopedic  chimique,  1888,  4  :  151. 


FRENCH  AGRICULTURAL  METHOD  393 

Another  and  more  rapid  method  for  dissolving  the  nitrate  may 
also  be  practiced.  In  a  flask  holding  about  one  liter,  place  220 
grams  of  the  soil  and  660  cubic  centimeters  of  distilled  water  and 
shake  vigorously,  or  enough  water  to  make  660  cubic  centimeters 
together  with  the  moisture  remaining  in  the  air-dried  sample 
taken.  All  the  nitrates  pass  into  solution.  Throw  the  contents  of 
the  flask  into  a  filter  and  use  600  cubic  centimeters  of  the  filtrate, 
which  will  contain  all  the  nitrates  in  200  grams  of  the  sample 
taken.  This  filtrate  is  evaporated  as  described  above. 

In  the  flat  dish  containing  the  dried  nitrates  pour  three  or  four 
cubic  centimeters  of  ferrous  chlorid  solution  and  stir  with  a  small 
glass  rod  until  complete  solution  of  the  nitrates  takes  place.  By 
means  of  a  small  funnel  the  solution  is  poured  into  C,  and  the 
capsule  and  funnel  are  well  rinsed  with  two  cubic  centimeters  of 
hydrochloric  acid.  The  washing  is  repeated  three  times,  as  above 
described,  and  once  with  one  cubic  centimeter  of  water,  which  is 
added  cautiously  so  as  to  form  a  layer  over  the  surface  of  the 
heavier  liquid.  The  tubulated  flask  is  then  connected  with  the 
carbon  dioxid  apparatus,  previously  freed  from  air,  and  the  gas 
allowed  to  flow  evenly  until  the  whole  of  the  interior  of  the  ap- 
paratus is  completely  air-free.  The  other  details  of  the  method 
are  essentially  the  same  as  those  adopted  by  the  Commission  of 
French  Agricultural  Chemists,  which  will  be  given  below. 

347.  The  French  Agricultural  Method. — The  Schloesing  method, 
as  practiced  by  the  French  agricultural  chemists,  is  very 
slightly  different  from  the  procedure  just  described.40  The  pro- 
cess with  soils  and  fertilizers  poor  in  nitrogen  is  carried  on  as 
follows : 

Five  hundred  grams  of  the  sample  are  introduced  into  a  flask  of 
about  two  liters  capacity  and  shaken  thoroughly  with  a  liter  of 
distilled  water.  The  whole  of  the  nitrates  of  the  soil  is  thus 
brought  into  solution.  The  solution  is  filtered  ana  400  cubic  cen- 
timeters of  the  filtrate  are  used,  which  correspond  to  200  grams 
of  the  soil.  This  liquid  is  evaporated  in  a  flask,  adding  a  frag- 
ment of  paraffin  to  prevent  foaming,  until  its  volume  is  reduced 
to  15  or  20  cubic  centimeters.  It  is  afterwards  transferred  through 
40  Annales  de  la  Science  agronomique,  1891,  1  :  263. 


394  AGRICULTURAL  ANALYSIS 

a  filter  into  a  capsule  with  a  flat  bottom,  in  which  the  evapora- 
tion is  finished  on  a  steam-bath,  taking  care  that  the  tempera- 
ture does  not  exceed  100°.  An  important  precaution  is  not  to 
allow  the  contact  of  the  water  with  the  soil  to  be  too  prolonged, 
to  avoid  the  reduction  of  the  nitrates  which  could  take  place 
under  the  influence  of  the  denitrifying  organisms  which  are  de- 
veloped with  so  great  a  rapidity  in  moist  earth.  The  apparatus 
in  which  the  transformation  of  the  nitrates  into  nitric  oxid  takes 
place  is  essentially  that  already  described  (Fig.  20).  The  car- 
bon dioxid  generator  is  connected  by  means  of  a  rubber  tube 
and  a  small  wash-bottle  to  the  small  retort  in  which  the  reaction 
takes  place,  and  from  which  the  exit  tube  leads  to  a  mercury 
trough.  The  gas  which  is  disengaged  is  received  under  a  jar 
drawn  out  to  a  fine  point  in  its  upper  part,  which  carries  about 
15  cubic  centimeters  of  potash  solution  containing  two  parts  of 
water  to  one  of  potash. 

The  operation  is  conducted  as  follows: 

Into  the  small  capsule  which  contains  the  dried  matter,  three 
or  four  cubic  centimeters  of  ferrous  chlorid  are  poured.  By 
means  of  a  stirring  rod  the  residue  sticking  to  the  sides  of  the 
capsule  is  detached  with  care,  and  all  the  matter  is  thus  collected 
in  the  bottom.  By  means  of  a  small  funnel  the  contents  of  the 
capsule  are  introduced  into  the  retort.  About  two  cubic  centi- 
meters of  hydrochloric  acid  are  used  for  washing  out  the  mate- 
rials, and  this  acid  is  also  introduced  into  the  retort.  The  wash- 
ing with  hydrochloric  acid  is  repeated  three  or  four  times,  and 
finally  the  apparatus  is  washed  with  one  cubic  centimeter  of 
water,  which  is  also  poured  in  by  the  small  funnel  with  great 
care,  so  that  this  water  may  form  a  layer  over  the  surface  of  the 
liquid.  The  apparatus  is  now  connected  and  filled  completely 
with  carbon  dioxid.  Since  it  is  necessary  that  this  gas  should 
be  completely  free  of  air,  the  flask  which  generates  it  is  first 
filled  with  the  acidulated  water  from  the  acid  flask,  and  the  air 
is  thus  almost  totally  displaced  by  the  liquid.  The  evolution  of 
carbon  dioxid  gas  which  follows,  completely  frees  the  apparatus 
from  air.  When  this  is  accomplished  the  retort  is  connected 
with  the  rest  of  the  apparatus  and  the  gas  allowed  to  pass  for 


FRENCH  AGRICULTURAL  METHOD  395 

about  two  minutes  until  the  air  is  completely  driven  out  of  all 
the  connections.  The  current  is  arrested  for  a  moment  by  pinch- 
ing the  rubber  tube  which  conducts  the  carbon  dioxid  into  the 
retort,  and  the  vessel  which  is  to  receive  the  gas  is  then  placed 
over  the  delivery  tube,  this  vessel  being  filled  with  mercury  and 
a  strong  solution  of  potash.  The  communication  between  the 
retort  and  the  carbon  dioxid  flask  is  broken  and  the  flask  is 
heated  slightly  by  means  of  a  small  lamp.  The  first  bubbles  of 
gas  evolved  should  be  entirely  absorbed  by  the  potash.  This  will 
be  an  indication  of  the  complete  absence  of  the  air.  When  the 
liquid  is  in  a  state  of  ebullition  the  nitrogen  dioxid  is  set  free. 
The  boiling  is  regulated  in  such  a  way  that  the  evolution  is  reg- 
ular and  the  liquid  of  the  retort  may  not,  by  a  too  violent  boiling, 
pass  into  the  receiver.  The  boiling  is  continued  until  the  larger 
part  of  the  liquid  is  distilled  and  only  three  or  four  cubic  centi- 
meters remain  in  the  retort.  At  this  time  a  few  bubbles  of  carbon 
dioxid  are  allowed  to  flow  through  in  order  to  cause  to  pass  into 
the  receiver  the  last  traces  of  nitric  oxid.  The  gas  received  is  left 
for  some  minutes  in  contact  with  the  potash. 

Afterward,  in  a  small  flask,  G,  the  neck  of  which  is  drawn  out 
to  a  fine  point,  and  carrying  a  bulb-tube,  H,  and  a  piece  of  rub- 
ber tubing,  there  are  boiled  25  or  30  cubic  centimeters  of  water 
for  five  or  six  minutes  in  order  to  drive  all  the  air  out  of  the 
flask,  and  while  the  boiling  is  continued  the  rubber  tubing  is 
fastened  to  the  drawn-out  part  of  the  jar  containing  the  nitric 
oxid.  Within  the  rubber  tubing  the  drawn-out  point  is  broken 
and  the  vapor  of  water  is  forced  into  the  jar  and  drives  before 
it  the  solution  of  potash  which  has  filled  the  capillary  part  of 
the  drawn-out  tube.  As  soon  as  the  point  is  broken,  the  boiling 
of  the  flask  is  stopped  and  by  its  cooling  the  nitric  oxid  passes 
into  it.  It  is  necessary  to  press  the  rubber  tubing  with  the  fingers 
in  order  that  the  passage  of  the  gas  into  the  flask  be  not  too  rapid. 
As  the  solution  of  potash  rises  in  the  bell-jar  which  contains  the 
nitric  oxid  near  to  the  point  where  the  rubber  tubing  covers  its 
drawn-out  portion,  the  fingers  are  removed  and  a  clamp  put  in 
their  place.  There  still  remains  a  little  nitric  oxid  in  the  flask, 
and  to  drive  this  out  it  is  necessary  to  introduce  five  or  six  cubic 


396  AGRICULTURAL  ANALYSIS 

centimeters  of  pure  hydrogen,  which  are  allowed  to  pass  over 
into  the  receiving  flask  by  releasing  the  clamp  in  the  same  way 
as  for  the  nitric  oxid.  The  hydrogen  being  introduced  in  succes- 
sive portions,  finally  carries  all  the  nitric  oxid  into  the  flask  with- 
out allowing  any  of  the  potash  to  enter. 

The  flask  containing  the  nitric  oxid  is  now  connected  with  a 
reservoir  of  oxygen.  The  oxygen  is  allowed  to  enter,  bubble  by 
bubble,  meanwhile  cooling  the  flask  by  immersion  in  water.  The 
transformation  of  nitric  oxid  into  nitric  acid  is  not  entirely  com- 
plete until  after  24  hours.  It  is  necessary,  therefore,  to  wait  so 
long  after  the  introduction  of  the  oxygen  before  determining 
the  amount  of  nitric  acid  produced. 

The  contents  of  the  flask  are  placed  in  a  titration-jar,  the  flask 
being  washed  two  or  three  times  and  a  few  drops  of  tincture  of 
litmus  being  added.  The  nitric  acid  is  then  determined  by  a 
standard  solution  of  calcium  hydroxid  or  some  other  standard 
alkali.  From  the  titration  the  content  of  nitric  acid  is  calcu- 
lated. 

The  French  committee  further  suggests  that  this  method  may 
be  modified  in  the  way  of  making  it  more  rapid  by  collecting 
the  nitric  acid  in  a  graduated  tube  filled  with  mercury  and  con- 
taining some  potash.  The  volume  of  the  gas  is  determined  and 
the  pressure  of  the  barometer  together  with  the  temperature  are 
observed ;  then  the  usual  calculations  are  made  to  reduce  the  vol- 
ume to  zero  and  to  a  pressure  of  760  millimeters  of  mercury. 
Each  cubic  centimeter  of  nitric  oxid  thus  measured  corresponds 
to  2.417  milligrams  of  nitric  acid.  The  presence  of  organic  mat- 
ter does  not  interfere  with  the  determination  of  nitric  acid  by 
either  of  the  methods  given  above. 

348.  Method  of  the  French  Sugar  Chemists. — The  nitrogen 
in  Chile  saltpeter  is  estimated  by  the  French  chemists  according 
to  the  method  of  Schloesing.  In  order  to  avoid  the  trouble  of 
calculating  the  results  from  the  volume  of  nitric  oxid  obtained, 
a  determination  is  first  made  with  a  pure  salt,  sodium  or  potassium 
nitrate.  The  volume  of  gas  obtained  is  read  directly  without 
correction  and  used  for  direct  comparison,  which  is  made  as 
follows : 


METHOD  OF  SCHLOESING-WAGNER  397 

The  solutions  of  the  pure  salts  and  of  the  sample  to  be  analyzed 
are  made  of  such  a  strength  as  to  contain  66  grams  of  sodium 
nitrate,  or  80  grams  of  potassium  nitrate,  in  a  liter.  Five  cubic 
centimeters  of  such  a  solution  will  yield  a  little  less  than  100 
cubic  centimeters  of  nitric  oxid  under  usual  conditions.  Let 
the  volume  of  gas  obtained  with  the  pure  salt  be  v,  and  that 
with  the  sample  be  v' .  The  calculation  is  then  made  from  the 

»'  x 

equation  :  —  = . 

v          100 

Example. — Let  95  cubic  centimeters  be  the  volume  of  gas  from 
five  cubic  centimeters  of  the  pure  salt  (sodium  nitrate),  and  91.5 
cubic  centimeters  be  the  volume  of  gas  from  five  cubic  centi- 
meters of  the  sample;  then  — —  =  -  ,  whence  x  =  96.  *i. 

95  ioo 

Hence  the  sample  analyzed  contains  96.31  per  cent,  of  sodium 
nitrate.  Since  the  pure  sodium  nitrate  contains  16.47  Per  cent,  of 

nitrogen,  the  sample  under  examination  would  contain— 

—  15.86  per  cent. 

It  is  evident  that  this  comparative  method  is  quite  easy  of  ap- 
plication when  the  sample  under  examination  has  no  other  nitrate 
in  it  except  that  combined  with  the  one  base. 

349.  Method  of  Schloesing-Wagner. — The  schloesing-wagner 
method  for  estimating  nitrogen  in  the  nitrates  of  fertilizers  is 
carried  out  at  the  Halle  experiment  station  as  follows :" 

A  flask,  Fig.  21,  of  about  250  cubic  centimeters  capacity,  is 
provided  with  a  rubber  stopper  with  two  holes.  Through  one 
of  them  is  passed  the  stem  of  a  funnel  carrying  a  glass  stop-cock. 
The  other  carries  a  delivery  tube  leading  to  the  receiving  vessel. 
The  end  of  the  delivery  tube  is  bent  so  as  to  pass  easily  under 
the  mouth  of  the  measuring  burette  and  is  covered  with  a  piece 
of  rubber  tubing. 

Fifty  cubic  centimeters  of  saturated  ferrous  chlorid  solution 
and  the  same  quantity  of  10  per  cent,  hydrochloric  acid  are 
placed  in  the  flask.  The  ferrous  chlorid  solution  is  obtained 

41  Bielerand  Schneidewind,    Die  agricultur-chemische  Versuchsstation, 
Halle  a  S,  1892  :  51. 


398 


AGRICULTURAL   ANALYSIS 


by  dissolving  nails  or  other  small  pieces  of  iron  in  hot  hydro- 
chloric acid  and  it  is  kept  in  glass  stoppered  flasks,  of  about  50 
cubic  centimeters  capacity,  entirely  filled.  The  content  of  one 
flask  is  enough  for  about  12  determinations  and  by  using  the 
whole  content  of  a  flask  as  soon  as  possible  after  opening,  any 
danger  of  oxidation,  which  would  take  place  in  a  large  flask 
frequently  opened,  is  avoided. 

The  contents  of  the  flask  are  boiled  until  all  the  air  is  driven 
off.  The  delivery  tube  is  then  placed  under  the  measuring 
tube,  which  is  filled  with  40  per  cent,  potash-lye.  The  measur- 
ing tube  is  previously  almost  filled  with  potash-lye  and  then  a 


Fig.  21.    Schloesing- Wagner  Apparatus. 

few  drops  of  water  added  and  the  tube  covered  with  a  piece  of 
filter  paper.  By  a  careful  and  quick  inversion  the  measuring 
tube  can  be  brought  into  the  vessel  receiving  it  without  any  dan«- 
ger  of  air  entering.  The  boiling  is  continued  for  some  time  and 
when  no  more  air  escapes,  the  end  of  the  delivery  tube  is  brought 
into  another  freshly  filled  measuring  tube  and  the  estimation  is 
commenced. 

Ten  cubic  centimeters  of  a  normal  saltpeter  solution,  contain- 
ing two  and  a  half  grams  of  pure  sodium  nitrate  in  100  cubic 
centimeters  are  placed  in  the  funnel  and,  with  continued  boiling, 
allowed  to  pass,  drop  by  drop,  into  the  flask.  When  almost  all 
has  run  out  the  funnel  is  washed  three  times  with  10  cubic  cen- 


MODIFICATION    OF    WARINGTON 


399 


timeters  of  10  per  cent,  hydrochloric  acid  and  this  is  allowed  to 
pass,  drop  by  drop,  into  the  flask.  When  no  more  nitric  oxid  is 
evolved  the  measuring  tube  is  transferred  to  a  large  jar  filled 
with  distilled  water. 

The  solution  of  the  substance  to  be  examined  should  be  used 
in  such  quantity  as  will  give  about  the  same  quantity  of  gas 
as  is  furnished  by  the  10  cubic  centimeters  test  nitrate  solution 
before  described ;  viz.,  about  70  cubic  centimeters.  Eight 
or  10  determinations  can  be  made,  one  following  the  other,  and 
finally  another  determination  with  normal  sodium  nitrate 
solution  should  be  made  as  a  check.  At  the  end  of  the  opera- 


Fig.  22.    Warington's  Apparatus  for  Nitric  Acid. 

tion  of  all  the  measuring  tubes  are  in  the  large  jar  filled  wtih 
distilled  water.  The  temperature  of  the  surrounding  water  will 
soon  be  imparted  to  the  contents  of  each  tube  and  the  volume  of 
nitric  oxid  is  read  by  bringing  the  level  within  and  without  the 
measuring-tube  to  the  same  point.  The  percentages  are  calcu- 
lated for  the  given  temperature  and  barometer  pressure  in  the 
usual  way ;  or  to  avoid  computation,  the  volume  can  be  com- 
pared directly  with  the  volume  furnished  by  the  normal  nitrate 
solution,  which  is  a  much  simpler  method. 

350.  Modification  of  Warington. — The  method  of  procedure 
and  description  of  apparatus  used,  as  employed  by  Warington, 
are  as  follows : 

The  vessel  in  which  the  reaction  takes  place  is  a  small  tubu- 
lated receiver,  A  (Fig.  22),  about  four  centimeters  in  diame- 


4OO  AGRICULTURAL  ANALYSIS 

,ter,  mounted  and  connected  as  shown  in  the  illustration.  The 
delivery  tube  dips  into  a  jar  of  mercury  in  a  trough  containing 
the  same  liquid.  The  long  supply  funnel-tube  a  is  of  small 
bore,  holding  in  all  only  one-half  cubic  centimeter.  The  con- 
necting tube,  F,  carrying  a  clamp,  is  also  of  small  diameter  and 
serves  to  connect  the  apparatus  with  a  supply  of  carbon  dioxid. 

In  practice,  the  supply  tube  a  is  first  filled  with  strong  hydro- 
chloric acid  and  carbon  dioxid  passed  through  the  apparatus  un- 
til the  air  is  all  .expelled.  This  is  indicated  when  a  portion  of  the 
gas  collected  over  the  mercury,  is  entirely  absorbed  by  caustic 
alkali. 

At  this  point  the  current  of  carbon  dioxid  is  stopped  by  the 
clamp  C,  and  a  bath  of  calcium  chlorid,  B,  heated  to  140°  is 
brought  under  the  bulb  A,  until  the  latter  is  half  immersed 
therein.  The  temperature  of  the  bath  is  maintained  by  a  lamp. 
By  allowing  a  few  drops  of  hydrochloric  acid  to  enter  the  receiver, 
the  carbon  dioxid  is  almost  wholly  expelled.  The  end  of  the 
delivery  tube  is  then  connected  with  the  tube,  T,  filled  with 
mercury,  and  the  apparatus  is  ready  for  use. 

The  nitrate,  in  which  the  nitric  acid  is  to  be  determined,  in  a 
dry  state,  is  dissolved  in  two  cubic  centimeters  of  the  ferrous 
chlorid  solution  (one  gram  of  iron  in  10  cubic  centimeters),  one 
cubic  centimeter  of  strong  hydrochloric  acid  is  added,  and  the 
whole  is  then  introduced  into  the  receiver  through  the  supply- 
tube,  being  followed  by  successive  rinsings  \vith  hydrochloric 
acid,  each  rinsing  not  exceeding  one-half  cubic  centimeter.  The 
contents  of  the  receiver  are,  in  a  few  moments,  boiled  to  dryness ; 
a  little  carbon  dioxid  is  admitted  before  dryness  is  reached,  and 
again  afterwards  to  drive  over  all  remains  of  nitric  oxid.  In 
the  recovered  gas  the  carbon  dioxid  is  first  absorbed  by  caustic 
potash,  and  afterwards  the  nitric  oxid  by  ferrous  chlorid.  All 
measurements  of  the  gas  are  made  in  Frankland's  modification 
of  Regnault's  apparatus.  The  carbon  dioxid  should  be  as  free 
as  possible  from  oxygen.  The  carbon  dioxid  generator  is  formed 
of  two  vessels,  the  lower  one  consisting  of  a  bottle  with  a  tubule 
in  the  side  near  the  bottom ;  this  bottle  is  supported  in  an  inverted 
position  and  contains  the  marble  from  which  the  gas  is  generated. 


MODIFICATION    OF    WARINGTOX  4OI 

The  upper  vessel  consists  of  a  similar  bottle  standing  upright  and 
containing  the  hydrochloric  acid  required  to  act  on  the  marble. 
The  two  vessels  are  connected  by  a  glass  tube  passing  from  the 
side  tubule  of  the  upper  vessel  to  the  inverted  mouth  of  the  lower 
vessel.  The  acid  from  the  upper  vessel  thus  enters  below  thr 
marble.  Carbon  dioxid  is  generated  and  removed  at  pleasure 
by  opening  a  stop-cock  attached  to  the  side  tubule  of  the  lower 
vessel  thus  allowing  hydrochloric  acid  to  descend  and  come  in 
contact  with  the  marble.  A  good  Kipp's  generator  of  any  ap- 
proved form  may  also  be  used  instead  of  the  simple  apparatus 
above  described. 

The  fragments  of  marble  used  are  previously  boiled  in  water 
in  a  strong  flask.  After  boiling  has  proceeded  for  some  time,  a 
rubber  stopper  is  fixed  in  the  neck  of  the  flask  and  the  flame 
removed.  Boiling  will  then  continue  for  some  time  in  a  partial 
vacuum. 

The  hydrochloric  acid  is  also  well  boiled  and  has  dissolved  in 
it  a  moderate  quantity  of  cuprous  chlorid.  As  soon  as  the  acid 
has  been  placed  in  the  upper  reservoir,  it  is  covered  by  a  layer 
of  oil.  The  apparatus  being  thus  charged  is  at  once  set  in  active 
work  by  opening  the  stop-cock  of  the  marble  reservoir ;  the  acid 
descends,  enters  the  marble  reservoir,  and  the  carbon  dioxid 
produced  drives  out  the  air.  As  the  acid  reservoir  is  kept  on  a 
higher  level  than  the  marble  reservoir,  the  latter  is  always  under 
internal  pressure,  and  leakage  of  air  from  without,  into  the  ap- 
paratus, can  not  occur. 

The  presence  of  the  cuprous  chlorid  in  the  hydrochloric  acid 
not  only  insures  the  removal  of  dissolved  oxygen,  but  affords  an 
indication  to  the  eye  of  the  maintenance  of  this  condition.  While 
the  acid  remains  of  an  olive  tint,  oxygen  is  absent;  but  should 
the  color  change  to  a  blue-green,  more  cuprous  chlorid  must 
be  added.  All  the  reagents  employed  should  be  previously  boiled. 

In  order  to  secure  absolute  freedom  from  air,  the  following 
modifications  on  the  above  process  have  been  adopted  by  War- 
ington.  The  apparatus  having  been  mounted  as  described,  the 
funnel-tube  attached  to  the  bulb  retort  is  filled  with  water,  and 
the  apparatus  connected  with  the  carbon  dioxid  generator.  Car- 


402  AGRICULTURAL  ANALYSIS 

bon  dioxid  is  then  passed  through  the  apparatus  until  a  moder- 
ate stream  of  bubbles  rise  in  the  mercury  trough.  The  stop- 
cock is  left  in  this  position,  and  the  admission  of  gas  is  con- 
trolled by  the  pinch-cock.  The  bath  of  calcium  chlorid  is  so 
adjusted  as  to  cause  the  bulb  retort  to  be  almost  entirely  sub- 
merged, and  the  temperature  of  the  bath  is  kept  at  130°  to  140°. 
Small  quantities  of  water  are  next  admitted  into  the  bulb  and 
expelled  as  steam  in  the  current  of  carbon  dioxid,  the  supply 
of  this  gas  being  shut  off  before  the  evaporation  is  entirely  com- 
pleted, so  as  to  leave  as  little  carbon  dioxid  as  possible  in  the 
apparatus.  Previous  to  very  delicate  experiments  it  is  advisable 
to  introduce  through  the  funnel-tube  a  small  quantity  of  potas- 
sium nitrate,  ferrous  chlorid,  and  hydrochloric  acid,  rinsing  the 
tube  with  the  latter  reagent.  .Any  trace  of  oxygen  remaining 
in  the  apparatus  is  then  consumed  by  the  nitric  oxid  formed ; 
and  after  boiling  to  dryness  and  driving  out  the  nitric  acid  with 
carbon  dioxid,  the  apparatus  is  in  a  perfect  condition  for  a  quan- 
titative experiment. 

351.  Preparation  of  the  Materials  to  be  Analyzed. — According 
to  Warington,  soil  extracts  may  be  used  without  other  preparation 
than  concentration. 

Vegetable  juices  which  coagulate  when  heated  require  to  be 
boiled  and  filtered  or  else  evaporated  to  a  thin  sirup,  treated, 
with  alcohol,  and  filtered.  A  clear  solution  being  thus  obtained, 
it  is  concentrated  over  a  water  bath  to  a  minimum  volume  in  a 
beaker  of  small  size.  As  soon  as  cool,  it  is  mixed  with  one 
cubic  centimeter  of  a  cold  saturated  solution  of  ferrous  chlorid 
and  one  cubic  centimeter  of  hydrochloric  acid,  both  reagents 
having  been  boiled  and  cooled  immediately  before  use. 

In  mixing  with  the  reagents,  care  must  be  taken  that  bubbles 
of  air  are  not  entangled,  which  is  apt  to  occur  with  viscid  extracts. 

The  quantity  of  ferrous  chlorid  mentioned  is  amply  sufficient 
for  most  extracts,  but  it  is  well  to  use  two  cubic  centimeters 
in  the  first  experiment,  the  presence  of  a  considerable  excess  of 
ferrous  chlorid  in  the  retort  being  thus  insured.  With  bulky 
vegetable  extracts  more  ferrous  chlorid  should  be  employed. 
To  the  sirup  from  20  grams  of  mangel-wurzel  sap,  five  cubic 


SCHULZE-TIEMANN   METHOD  403 

centimeters  of  ferrous  chlorid  and  two  cubic  centimeters  of  hydro- 
chloric acid  are  usually  added. 

352.  Measurement  of  the  Gas. — The  measurement  of  the  gas 
was  for  some  time  conducted  by  the  use  of  concentrated  potash 
for  absorbing  the  carbon  dioxid,  and  ferrous  chlorid  for  absorbing 
the  nitric  oxid.     The  use  of  the  ferrous  chlorid,  however,  was 
found  to  introduce  a  source  of  error.     The  treatment  of  the  gas 
with  oxygen  and  pyrogallol  over  potash  has,  therefore,  been  sub- 
stituted by  Warington  for  absorption  by  ferrous  chlorid. 

The  chief  source  of  error  attending  the  oxygen  process  lies  in 
the  small  quantity  of  carbon  monoxid  produced  during  the 
absorption  with  pyrogaliol,  but  this  error  becomes  negligible  if  the 
oxygen  be  onjy  used  in  small  excess.  The  amount  of  oxygen 
employed  can  be  regulated  by  the  use  of  Bischof's  gas  delivery 
tube.  This  may  be  made  of  a  test-tube  having  a  small  perfora- 
tion half  an  inch  from  the  mouth.  The  tube  is  partly  filled  with 
oxygen  over  mercury,  and  its  mouth  is  then  closed  by  a  finely 
perforated  stopper  made  from  a  piece  of  wide  tube  and  fitted 
tightly  into  the  test-tube  by  means  of  a  covering  of  rubber. 
When  this  tube  is  inclined,  the  side  perforation  being  down- 
wards, the  oxygen  is  discharged  in  small  bubbles  from  the  per- 
forated stopper,  while  mercury  enters  through  the  opening. 
Using  this  tube,  the  supply  of  oxygen  is  perfectly  under  control 
and  can  be  stopped  as  soon  as  a  fresh  bubble  ceases  to  produce 
a  red  tinge  on  entering.  Warington  concludes  his  description 
by  stating  that  in  the  reaction  proposed  by  Schloesing  the 
analyst  has  a  means  of  determining  a  very  small  quantity  of 
nitric  acid  with  considerable  accuracy,  even  in  the  presence  of 
organic  matter;  but  to  accomplish  this,  the  various  simplifica- 
tions consisting  in  the  omission  of  the  stream  of  carbon  dioxid, 
and  the  collection  of  the  gas  over  caustic  soda  must  be  aban- 
doned, and  special  precautions  must  be  taken  to  exclude  all 
traces  of  oxygen  from  the  apparatus. 

353.  Schulze-Tiemann  Method. — The  modification  of  Schulze- 
Tiemann  in  the  ferrous  salt  method  consists  chiefly  in  the  omis- 
sion of  the  use  of  carbon  dioxid,  and  in  the  simplified  form  of 
apparatus,  which  permits   rapid  work  and  gives,   also,   accord- 


404 


AGRICULTURAL  ANALYSIS 


ing  to  some  authorities,  very  exact  and  reliable  results.42  The 
extract,  representing  500  grams  of  the  fine  soil,  is  reduced  by  evap- 
oration to  loo  cubic  centimeters  and  placed  in  a  glass  flask,  A 
(Fig.  23),  of  500  cubic  centimeters  capacity.  The  flask  is  closed 
with  a  rubber  stopper,  carrying  two  bent  glass  tubes  which  pass 
through  it.  The  tube  a  b  c  is  drawn  out  into  a  point  at  a  and 
reaches  about  two  centimeters  below  the  surface  of  the  rubber 
stopper.  The  tube  e  f  g  passes  just  to  the  lower  surface  of  the 


Fig.  23.     Schulze-Tiemann's  Nitric  Acid  Apparatus. 

rubber  stopper.  The  two  tubes  mentioned  are  connected,  by 
means  of  rubber  tubes  and  pinch-cocks,  with  the  tubes  d  and  h. 
The  pinch-cocks  at  c  and  g  must  be  capable  of  closing  the  tubes 
air-tight.  The  end  of  the  tube  g  h  passes  into  a  crystallizing 
dish,  B,  and  is  bent  upward  to  a  point  passing  two  to  three  cen- 
timeters into  the  measuring  tube  C.  The  point  within  the  tube 
is  covered  with  a  piece  of  rubber  tubing.  The  measuring  tube  C 
is  divided  into  tenths  of  a  cubic  centimeter,  and  together  with 
the  crystallizing  dish,  B,  is  filled  with  a  10  per  cent,  solution  of 

42  Zeitschrift  fur  analytische  Chemie,  1870,  9  :  24,  401. 
Die  landwirtschaftlichen  Versuchs-Stationen,  1867,  9  :  9. 
Berichte  der  deutschen  chemischen  Gesellschaft,  1873,  6  :  1038. 


SCHULZE-TIEMANN   METHOD  405 

boiled  soda-lye,  which  is  obtained  by  dissolving  12.9  parts  of 
sodium  hydroxid  in  100  parts  of  water. 

The  liquid  which  is  to  be  examined  for  nitric  acid  (the  pinch- 
cocks  being  opened  and  the  tube  g  h  not  dipping  into  the  crys- 
tallizing dish),  is  boiled  for  one  hour  in  order  to  drive  the  air 
out  of  the  flask  A.  The  end  of  the  tube  e  f  g  h  is  then  brought 
into  the  crystallizing  dish  containing  the  sodium  hydroxid  solu- 
tion so  that  the  steam  escaping  from  the  flask,  A,  escapes  partly 
through  the  tube  bed  and  partly  through  the  tube  f  g  h,  not 
allowing,  however,  the  bubbles  to  enter  the  measuring  tube  C. 
To  determine  whether  the  air  is  all  expelled,  the  pinch-cock  at  g 
is  closed  and  the  soda-lye  will  thereupon  rise  to  g  in  case  no  air 
interferes.  It  is  best  to  close  the  tube  at  g  first  with  the  thumb 
and  finger,  and  then  the  rise  of  the  soda-lye  to  that  point  can  be 
determined  by  the  impulse  felt  The  tube  is  then  firmly  closed  by 
means  of  the  pinch-cock  g.  The  rest  of  the  steam  is  allowed 
to  escape  through  the  tube  abed,  and  the  evaporation  is  con- 
tinued until  the  contents  of  the  flask  are  evaporated  to  about  10 
cubic  centimeters.*  The  flask  into  which  the  tube  c  d  dips  is 
filled  with  freshly  boiled  water.  The  lamp  is  removed  from  the 
flask  A,  the  pinch-cock  is  closed,  whereupon  the  tube  c  d  be- 
comes filled  with  the  freshly  boiled  water.  The  measuring  tube, 
C,  filled  with  freshly  boiled  soda-lye,  is  closed  with  the  thumb 
and  brought  into  the  dish  B,  care  being  taken  that  no  bubble 
of  air  enters.  It  is  placed  over  the  end  of  the  tube  g  h. 

The  pressure  of  the  external  air  will  now  flatten  the  rubber 
tubes  at  c  and  g.  The  flask  at  the  end  of  c  d,  holding  freshly 
boiled  water,  is  then  replaced  with  one  filled  with  a  nearly  satu- 
rated solution  of  ferrous  chlorid  containing  some  hydrochloric 
acid.  The  flask  containing  the  ferrous  chlorid  solution  should 
be  graduated  so  that  the  amount  which  is  sucked  into  the  flask 
A  can  be  determined.  The  pinch-cock  c  is  opened  and  from 
15  to  20  cubic  centimeters  of  the  ferrous  chlorid  solution  allowed 
to  flow  into  A.  The  end  of  the  tube  c  d  is  then  placed  in  an- 
other flask  containing  strong  hydrochloric  acid,  and  the  latter  al- 
lowed to  flow  into  the  tube  in  small  quantities  at  a  time  until 
all  the  ferrous  chlorid  is  washed  out  of  the  tube  bed  into  A. 


4°6  AGRICULTURAL  ANALYSIS 

At  the  point  b  there  is  sometimes  formed  a  little  bubble  of  hydro- 
chloric acid  in  the  state  of  gas,  which  by  heating  the  flask  A 
completely  disappears. 

The  flask  A  is  next  warmed  gently  until  the  rubber  tubes  at 
the  pinch-cocks  begin  to  assume  their  normal  condition.  The 
pinch-cock  at  g  is  now  replaced  by  the  thumb  and  finger,  and  as 
soon  as  the  pressure  within  the  flask  A  is  somewhat  stronger, 
caused  by  the  nitric  oxid  gas  evolved  from  the  mixture,  it  is 
allowed  to  pass  through  the  tube  e  f  g  h  and  escape  into  the  meas- 
uring cylinder  C.  By  a  manipulation  of  the  finger  and  thumb 
at  g,  it  is  possible  to  prevent  regurgitation  of  the  sodium  hydroxid 
into  A,  and  at  the  same  time  to  relieve  the  pressure  of  the  nitric 
oxid  in  A,  which  would  be  difficult  to  do  by  means  of  the  pinch- 
cock  alone. 

The  boiling  of  the  liquid  is  continued  until  there  is  no  longer 
any  increase  of  the  volume  of  gas  in  the  measuring  cylinder  C. 
After  the  end  of  the  operation  the  tube  g  h  is  removed  from  the 
dish  B  and  the  measuring  tube  C  is  closed  by  means  of  the 
thumb  while  its  end  is  still  beneath  the  surface  of  the  soda-lye, 
and  it  is  shaken  until  all  traces  of  any  hydrochloric  acid  which 
may  have  escaped  absorption  are  removed.  It  is  then  placed 
in  a  large  glass  cylinder  filled  with  water  at  the  temperature 
at  which  the  volume  of  gas  is  to  be  read.  After  being  kept  at 
this  constant  temperature  for  about  half  an  hour  the  volume  of 
the  nitric  oxid  can  be  read.  For  this  purpose  the  measuring 
cylinder  C  is  sunk  into  the  water  of  the  large  cylinder  until 
the  level  of  the  liquids  within  and  without  the  tube  is  the  same. 
The  usual  correction  for  pressure  of  the  atmosphere,  as  deter- 
mined by  the  barometer,  and  for  the  tension  of  the  aqueous 
vapor  at  the  temperature  at  which  the  reading  is  made,  is  ap- 
plied. The  correction  is  made  by  means  of  the  following  formula : 

v,  as  V  X  273  X  (B  -/) 
(273  +  t)    X   760 

In  this  formula  V  denotes  the  volume  of  the  gas  at  the  tem- 
perature of  zero  and  at  760  millimeters  barometric  pressure;  V, 
the  volume  of  the  gas  as  read  at  the  barometric  pressure  observed, 


:mp. 

Tension  in  mm. 

Temp. 

Tension  in  mm. 

Temp. 

> 

mercury. 

o 

mercury. 

0 

0 

4-6 

9 

8-5 

IS 

I 

4-9 

10 

9-i 

19 

2 

5-3 

ii 

9-7 

20 

3 

5-7 

12 

10.4 

21 

4 

6.1 

13 

II.  I 

22 

5 

6.5 

H 

11.9 

23 

6 

6-9 

15 

12.7 

24 

7 

7-4 

16 

13-5 

25 

8 

8.0 

17 

14.4 

26 

SPIEGEL'S  MODIFICATION  407 

B,  and  the  temperature  observed,  /,  while  /  denotes  the  tension 
of  the  aqueous  vapor  in  millimeters  of  mercury  pressure  at  the 
observed  temperature,  t.  The  tension  of  the  aqueous  vapor  at 
temperatures  from  zero  to  26°,  expressed  in  millimeters  of  mer- 
cury, is  given  in  the  following  table: 

Tension  in  mm. 
mercury. 

15-3 
16.3 
17.4 
18.5 
19.6 
20.9 
22.2 

23-5 
25.0 

From  the  gas  volume  corrected  by  the  above  formula  the  nitric 
acid  is  calculated  as  follows : 

One  cubic  centimeter  of  nitric  oxid  weighs  at  o°  and  760  milli- 
meters barometric  pressure  1.343  milligrams. 

Since  two  molecules  of  NO  (molecular  weight  60)  correspond 
tc  one  molecule  of  N2O5  (108),  we  have  the  following  equa- 
tion: 60  :  108  —  i.343:x.  Whence  x  =:  2.417  milligrams,  the 
weight  of  nitric  acid  (N2O5)  corresponding  to  one  cubic  centi- 
meter of  nitric  oxid. 

354.  Spiegel's  Modification. — Spiegel  noticed  inaccuracies  in 
the  results  of  the  ferrous  chlorid  method  of  estimating  nitric  acid 
when  carbon  dioxid  is  used,  which  sometimes  amounted  to  three 
per  cent,  of  the  nitric  acid  present  in  the  sample.  The  following 
suggestions  are  made  by  him  for  the  improvement  of  the  pro- 
cess :43 

As  regards  the  use  of  carbon  dioxid  in  the  operation,  the  first 
difficulty  consists  in  obtaining  it  entirely  free  from  air.  By  the 
use  of  small  pieces  of  marble,  which,  before  being  placed  in  the 
kipp  apparatus  are  kept  for  a  long  while  in  boiling  water,  a  pro- 
duct is  obtained  which,  after  30  minutes  of  moderate  evolution, 
leaves  only  a  trace  of  unabsorbed  gas  in  contact  with  potash-lye. 
The  apparatus  used  is  illustrated  in  Fig.  24. 

45  Berichte  der  deutschen  chemischen  Gesellschaft,  1890,  23  :  1361. 


408 


AGRICULTURAL  ANALYSIS 


A  is  a  round  flask  of  about  150  cubic  centimeters  capacity, 
furnished  with  a  well-fitting  rubber  stopper  provided  with  two 
holes,  one  for  the  entrance  of  the  funnel  tube  B  and  the  other 
for  the  delivery  tube  C.  The  tube  B  ends  about  two  centimeters 
above  the  bottom  of  A  and  carries  a  bulb-shaped  funnel  at  its  top 
capable  of  holding  about  50  cubic  centimeters.  The  gas  tube 
D  is  ground  into  the  bulb  of  B  as  shown  in  the  figure. 

After  the  flask  has  been  filled  with   the   solution  to  be  ex- 


Fig.  24.    Spiegel's  Apparatus  for  Nitric  Acid. 


amined,  carbon  dioxid  is  conducted  through  D  and  the  flask 
is  heated  to  boiling  until  the  gas  which  escapes  through  C  no 
longer  contains  any  air.  The  measuring  tube  is  brought  over 
the  end  of  the  delivery  tube  C,  in  the  usual  manner;  but  is  not 
shown  in  the  figure.  In  the  funnel  of  B  are  placed  20  cubic 
centimeters  of  previously  prepared  and  boiled  ferrous  chlorid 
solution  and  this  liquid  is  allowed  to  flow  partly  into  A  by  lift- 


ing  slightly  the  gas-tube  D.  About  40  cubic  centimeters  of 
concentrated,  boiled  hydrochloric  acid  are  afterwards  added  to  it 
in  the  same  way.  As  soon  as  the  liquid  in  the  flask  A  is  again 
boiling,  the  stream  of  carbon  dioxid  is  shut  off  and  allowed  to 
flow  again  only  towards  the  end  of  the  operation,  when  the  con- 
tents of  the  flask  are  reduced  almost  to  dryness.  As  will  be 
seen  from  the  above  directions,  no  unboiled  liquids  of  any  kind 
are  to  be  used  as  reagents  in  the  apparatus  described.  If  the 


Fig.  25.     De  Konnick's  Apparatus. 

flask  A  were  made  much  smaller  the  efficiency  of  this  apparatus 
would  be  increased.  It  appears  to  have  few,  if  any,  advantages 
over  Warington's  process. 

355.  De  Konnick's  Modification  of  Schloesing's  Method. — This 
modification  consists  in  an  arrangement  of  the  gas  delivery  tube, 
whereby  the  regurgitation  of  the  water  in  the  measuring  burette 
into  the  evolution  flask  is  prevented  by  a  device  for  sealing  the 


4-IO  AGRICULTURAL  ANALYSIS 

delivery  tube  with  mercury.44  The  apparatus  is  arranged  as 
shown  in  Fig.  25.  The  flask  in  which  the  decomposition  takes 
place  is  provided  with  a  long  neck,  into  which  a  side  tube  is 
sealed  and  bent  upwards,  carrying  a  small  funnel  attached  to  it 
by  rubber  tubing.  The  piece  of  rubber  tubing  carries  a  pinch- 
cock,  by  means  of  which  the  solution  containing  the  nitrate  and 
hydrochloric  acid  can  be  introduced  into  the  flask.  The  small 
gas  delivery  tube  is  arranged  as  shown  in  the  figure,  and  carries 
at  the  end  next  the  burette  a  device  shown  in  Fig.  26.  The  cork 
represented  in  this  device  has  radial  notches  cut  in  it,  so  as  to 
permit  of  a  free  communication  between  the  water  in  the  burette 
and  in  the  pneumatic  trough.  The  open  end  of  the  burette,  when 
the  apparatus  is  mounted  ready  for  use,  rests  on  the  notched  sur- 


Fig.  26.     End  of  Delivery  Tube. 


face  of  the  cork,  and  the  end  of  the  delivery  tube  is  placed  in  the 
crystallizing  dish  resting  on  the  bottom  of  the  pneumatic  trough. 

The  end  of  the  delivery  tube,  as  indicated,  has  fused  to  it  a 
vertical  tube,  open  at  both  ends  and  from  six  to  seven  centimeters 
in  length,  and  carrying  the  notched  cork  already  described.  The 
crystallizing  dish  in  the  bottom  of  the  pneumatic  trough  is  filled 
with  mercury  until  the  point  of  union  of  the  delivery  tube  with 
the  vertical  end  is  sealed  to  the  depth  of  a  few  millimeters.  As 
the  gas  is  evolved  it  bubbles  up  through  the  mercury  into  the 
measuring  tube  and  the  displaced  water  passes  out  through  the 
notches  in  the  cork.  Should  any  back  pressure  supervene,  the 
mercury  at  once  rises  in  the  delivery  tube,  which  is  of  such  a 
length  as  to  prevent  its  entrance  into  the  flask.  The  operation 
can  then  be  carried  on  with  absolute  safety. 

To  make  an  estimation,  there  are  placed  in  the  flask  about 
44  Zeitschrift  fur  analytische  Chemie,  1894,  33  :  200. 


SCHMIDT'S  PROCESS  411 

40  cubic  centimeters  of  ferrous  chlorid  solution  containing  about 
200  grams  of  iron  to  the  liter,  and  also  an  equal  volume  of  hydro- 
chloric acid  of  i.i  specific  gravity.  The  side  tube  is  also  filled 
up  to  the  funnel  with  the  acid.  The  contents  of  the  flask  are 
boiled  until  all  air  is  expelled,  which  can  be  determined  by  hold- 
ing a  test-tube  filled  with  water  over  the  end  of  the  delivery 
tube.  The  solution  containing  the  nitrate  is  next  placed  in  the 
funnel,  the  pinch-cock  opened  and  the  liquid  allowed  to  run  into 
the  flask  by  means  of  the  partial  vacuum  produced  by  stopping 
the  boiling  and  allowing  the  mercury  to  rise  in  the  delivery  tube. 
All  the  solution  is  washed  into  the  flask  by  successive  rinsings 
of  the  funnel  with  hydrochloric  acid,  being  careful  to  allow  no 
bubble  of  air  to  enter.  The  contents  of  the  flask  are  again 
raised  to  the  boiling-point  and  the  nitric  oxid  evolved  collected  in 
the  nitrometer.  The  solution  examined  should  contain  enough 
nitrate  to  afford  from  60  to  80  cubic  centimeters  of  gas.  With- 
out refilling  the  flask,  from  eight  to  nine  determinations  can  be 
made  by  regenerating  the  ferrous  chlorid  by  treatment  with  zinc 
chlorid.  Care  must  be  exercised  not  to  add  the  zinc  chlorid  in 
excess,  otherwise  ammonia  and  not  nitric  oxid  will  be  produced. 
The  side  tube  and  funnel  must  also  be  carefully  freed  from  zinc 
chlorid  by  washing  with  hydrochloric  acid. 

356.  Schmidt's  Process. — In  the  case  of  a  water,  or  the  aque- 
ous extract  of  a  soil,  according  to  the  content  of  nitric  acid, 
from  50  to  loo  cubic  centimeters  are  evaporated  to  30  cubic  cen- 
timeters, and  the  residue  sucked  into  the  generating  flask  of  the 
apparatus,  Fig.  27,  and,  with  the  rinsings  with  distilled  water, 
evaporated  again  to  from  20  to  30  cubic  centimeters,  and  the  flask 
then  connected,  as  shown  in  the  figure,  to  a  schiff  measuring 
apparatus  B.45  This  apparatus  is  previously  filled  to  i  with  mer- 
cury, and  the  bulb  g  connected  with  k  by  a  rubber  tube. 

The  apparatus  is  then  filled  with  a  20  per  cent,  caustic  soda 
solution  previously  boiled  and  still  warm,  until  the  bulb  g  is 
partially  filled  when  raised  a  little  above  the  cock  h.  Then  h  is 
closed  and  g  held,  by  an  appropriate  support,  on  about  the 
same  level  with  h.  The  cock  at  b  is  then  closed  and  e  opened. 
45  Apotheker  Zeitung,  1890,  5  :  287. 


412 


AGRICULTURAL  ANALYSIS 


Meanwhile  the  ebullition  in  the  flask  is  continued,  and  the  air 
bubbles  rising  in  the  schiff  apparatus  are  removed,  from  time  to 
time,  by  carefully  opening  h  and  raising  g.  When  bubbles  no 
longer  come  over,  the  cock  at  e  is  closed  and  at  b  opened,  and 
the  steam  issuing  at  a  is  conducted  through  a  mixture  of  ferrous 
chlorid  and  strong  hydrochloric  acid  to  free  it,  as  far  as  possible, 
from  air.  When  the  contents  of  the  flask  have  been  evaporated 


Fig.  27.    Schmidt's  Apparatus. 

to  about  five  cubic  centimeters,  b  is  closed  and  the  lamp  at  once 
removed. 

By  carefully  opening  b  about  10  cubic  centimeters  of  a  mix- 
ture of  ferrous  chlorid  and  hydrochloric  acid  are  allowed  to  enter 
the  flask,  when  b  is  closed  and  the  flask  slowly  heated  until  the 
positive  pressure  is  restored.  The  pinch-cock  e  is  then  opened 
and  the  contents  of  the  flask  evaporated  nearly  to  dryness.  The 
cock  e  is  again  closed  and  the  flame  removed.  Another  quan- 
tity (15  cubic  centimeters)  of  ferrous  chlorid  and  hydrochloric 
acid  solution  is  sucked  into  the  flask  and  the  process  of  distilla- 
tion repeated,  whereby  the  whole  of  the  nitric  oxid  is  collected 


MERCURY  AND  SULFURIC  ACID  METHOD  413 

in  h.  The  nitric  oxid  evolved  is  measured  in  the  usual  way  and 
calculated  to  nitric  acid,  one  cubic  centimeter  of  nitrogen  dioxid 
being  equal  to  2.417  milligrams  of  nitric  acid. 

357.  Merits   of  the   Ferrous  Chlorid  Process. — The   possibility 
of  an  accurate  determination  of  nitrates,  by  decomposition  with 
a  ferrous  salt  in  presence  of  an  excess  of  hydrochloric  acid,  has 
been  established  by  many  years  of  experience  and  by  the  testi- 
mony of  many  analysts.     The    method  is  applicable    especially 
where  the  quantity  of  nitrate  is  not  too  small  and  when  organic 
matter  is  present.     In  the  case  of  minute  quantities  of  nitrate, 
however,  the  process  is  inapplicable  and  must  give  way  to  some 
of  the  colorimetric  methods  to  be  hereafter  described. 

In  respect  of  the  apparatus,  modern  practice  has  led  to  the 
preference  of  that  form  which  does  not  require  the  use  of  carbon 
dioxid  for  displacing  the  air.  Steam  appears  to  be  quite  as  ef- 
fective as  carbon  dioxid  and  is  much  more  easily  employed.  That 
form  of  apparatus  should  be  used  which  is  the  simplest  in  con- 
struction and  has  the  least  cubical  content. 

The  measurement  of  the  evolved  gas  is  most  simply  made  by 
collecting  over  lye  in  an  azotometer,  reading  the  volume,  noting 
the  reading  of  the  barometer  and  thermometer  and  then  reducing 
to  standard  conditions  of  pressure  and  temperature  by  the  cus- 
tomary calculations.  Where  a  very  strong  lye  is  used  the  ten- 
sion of  the  aqueous  vapor  may  be  neglected.  While  every  analyst 
should  have  a  thorough  knowledge  of  the  ferrous  chlorid  method 
and  the  principles  on  which  it  is  based,  it  can  not  be  compared 
in  simplicity  to  the  later  methods  with  pure  nitrates,  which  are 
based  on  the  conversion  of  the  nitric  acid  into  ammonia  by  the 
action  of  nascent  hydrogen.  In  accuracy,  moreover,  it  does  not 
appear  to  have  any  marked  advantage  over  the  reduction  methods. 

358.  Mercury  and  Sulfuric  Acid  Method. — This  simple  and  ac- 
curate method  of  determining  nitric  acid  in  the  absence  of  organic 
matter  is  known  as  the  Crum-Franklarid  process.48 

The  method  rests  on  the  principle  of  converting  nitric  acid  into 

46  Philosophical  Magazine,  1847,  [3],  30  :  426. 
Journal  of  the  Chemical  Society,  1868,  21  :  101. 
Sutton,  Volumetric  Analysis,  gth  Edition,  1907  :  443, 


414  AGRICULTURAL  ANALYSIS 

nitric  oxid  by  the  action  of  mercury  in  the  presence  of  sulfuric 
acid.  The  operation  as  at  first  described  is  conducted  in  a  glass 
jar  eight  inches  long  by  one  and  a  half  inches  in  diameter,  filled 
with  mercury  and  inverted  in  a  trough  containing  the  same  liquid. 
The  nitrate  to  be  examined,  in  a  solid  form,  is  passed  into  the 
tube,  together  with  three  cubic  centimeters  of  water  and  five  of 
sulfuric  acid.  With  occasional  shaking,  two  hours  are  allowed 
for  the  disengagement  of  the  gas,  which  is  then  measured. 

359.  Warington's  Modification. — A  graduated  shaking-tube  is 
employed,  which  allows  the  nitrate  solution  and  oil  of  vitriol  to 
be  brought  to  a  definite  volume.47     The  nitrate  solution,  with  rins- 
ings, is  always  two  cubic  centimeters,  and  enough  sulfuric  acid 
is  added  to  increase  the  volume  to  five  cubic  centimeters.     The 
sulfuric  acid  should  give  no  gas  when  shaken  with  distilled  water. 
Any  gas  given  off  in  the  apparatus  before  shaking  is  not  expelled 
but  is  included  in  the  final  result.     The  persistent  froth  some- 
times noticed  where  some  kinds  of  organic  matter  are  present, 
is  reduced  by  the  addition  of  a  few  drops  of  hot  water  through 
the  stop-cock  of  the  apparatus.     The  nitric  oxid  is  finally  meas- 
ured in  Frankland's  modification  of  Regnault's  apparatus. 

This  method,  accurate  for  pure  nitrates,  unfortunately  fails  in 
the  presence  of  any  considerable  amount  of  organic  matter. 

According  to  Warington's  observations,  the  presence  of  chlo- 
rids  is  no  hindrance  to  the  accurate  determination  of  both  nitric 
and  nitrous  acids  by  the  mercury  method.  This  simplifies  the 
operation  as  carried  on  by  Frankland,  who  directs  that  any  chlorin 
present  be  removed  before  the  determination  of  the  nitric  acid  is 
commenced. 

360.  Noyes'  Method. — In    the    analyses    made    by    Noyes    for 
the  National  Board  of  Health,  the  Crum-Frankland  method  was 
employed.48     The  apparatus  used  was  essentially  that  which  is 
now  known  as  Lunge's  nitrometer,  and  it  will  be  described  in 
the  next  paragraph.     No  correction  is  made  by  Noyes  for  the 
tension  of  aqueous  vapor  in  the  measurement  of  the  nitric  oxid 
because  of  the  moderate  dilution  of  the  sulfuric  acid  by  the  liquid 

47  Journal  of  the  Chemical  Society,  1879,  35  :  376. 

48  Report  of  the  National  Board  of  Health,  1882  :  281. 


IvUNGE'S  NITROMETER 


415 


holding  the  nitric  compounds  in  solution.  The  chlorin  is  not  re- 
moved from  the  dry  residue  of  the  evaporated  water,  as  its  pres- 
ence in  moderate  quantity  does  not  interfere  with  the  accuracy 
of  the  process.  In  order  to  obtain  the  amount  of  nitrogen  in  the 
form  of  nitrates,  the  total  volume  of  nitric  oxid  must  be  dimin- 
ished by  that  due  to  nitrites  present,  which  must  be  determined  in 
a  separate  analysis.  The  method  of  manipulation  is  given  in  the 
following  paragraph. 

361.  Lunge's  Nitrometer. — The  apparatus  employed  by  Noyes, 
in  a  somewhat  more  elaborate  form,  is  known  as  Lunge's  nitrom- 
eter.*9 This  apparatus  is  shown  in  Fig.  28.  It  consists  of  a 


Fig.  28.    lounge's  Nitrometer. 


burette  a,  divided  into  one-fifth  cubic  centimeters.  At  its  upper 
end  it  is  expanded  into  a  cup-shaped  funnel  attached  by  a  three- 
way  glass  stop-cock.  Below,  the  burette  is  joined  to  a  plain  tube 
b,  of  similar  size,  by  means  of  rubber  tubing.  The  apparatus  is 
first  filled  with  mercury  through  the  tube  b,  the  stop-cock  being 
so  adjusted  as  to  allow  the  mercury  to  fill  the  cup  at  the  top  of  a. 
The  cock  is  then  turned  until  the  mercury  in  the  cup  flows  out 
49  Berichte  der  deutschen  chemischen  Gesellschaft,  1878,  1 1  :  437. 


4l6  AGRICULTURAL  ANALYSIS 

through  the  side  tube,  carrying  the  rubber  tube  and  clamp.  The 
three-way  cock  is  closed,  and  the  solution  containing  the  nitrate 
placed  in  the  cup.  By  lowering  the  tube  b  and  opening  the  cock 
the  liquid  is  carefully  passed  into  a,  being  careful  to  close  the 
cock  before  all  the  liquid  has  passed  out  of  the  cup.  By  repeated 
rinsings  with  pure  concentrated  sulfuric  acid,  every  particle  of  the 
nitric  compound  is  finally  introduced  into  a,  together  with  a  large 
excess  of  sulfuric  acid.  The  total  volume  of  the  introduced  liquid 
should  not  exceed  10  cubic  centimeters.  The  mixture  of  the  mer- 
cury, nitric  compound,  and  sulfuric  acid  is  effected  by  detaching 
a  from  its  support,  compressing  the  rubber  connection  between  a 
and  b,  placing  a  nearly  in  a  horizontal  position,  and  quickly  bring- 
ing it  into  a  vertical  position  with  vigorous  shaking. 

After  about  five  minutes  the  reaction  is  complete,  and  the  level 
of  the  liquids  in  the  two  tubes  is  so  adjusted  as  to  compensate 
for  the  difference  in  specific  gravity  between  the  acid  mixture  in 
a  and  the  mercury  in  b ;  in  other  words,  the  mercury  column  in  b 
should  stand  above  the  mercury  column  in  a  one-seventh  of  the 
length  of  the  acid  mixture  in  a.  This  secures  atmospheric  pres- 
sure on  the  nitric  oxid  which  has  been  collected  in  a.  The  meas- 
ured volume  of  nitric  oxid  should  be  reduced  to  o°  and  760  milli- 
meters barometric  pressure.  Each  cubic  centimeter  of  nitric  oxid 
thus  obtained  corresponds  to  1.343  milligrams  NO;  2.417  milli- 
grams N2O5;  1.701  milligrams  N2O3;  2.820  milligrams  HNOS ; 
4.521  milligrams  KNO3,  and  3.805  milligrams  NaNO3. 

362.  Lunge's  Improved  Apparatus. — Lunge  has  improved  his 
apparatus  for  generating  and  measuring  gases  and  extended  its 
applicability.60  The  part  of  it  designed  to  measure  the  volume  of 
a  gas  is  the  same  in  all  cases.  For  generating  the  gas,  the  ap- 
paratus varies  according  to  the  character  of  the  substance  under 
examination. 

The  measuring  apparatus  is  shown  in  Fig.  29.  It  is  composed 
essentially  of  three  tubes,  conveniently  mounted  on  a  wooden 
holder  with  a  box  base  for  saving  any  spilled  mercury.  The 
support  is  not  shown  in  the  illustration. 

The  tubes  A,  B,  C,  are  mutually  connected  by  means  of  a 
80  Bulletin  de  la  Soci£t£  chimique  de  Paris,  1894,  [3],  1 1  :  625. 


LUNGE'S  IMPROVED  APPARATUS 


three-way  tube  and  rubber  tubing,  with  very  thick  walls  to  safely 
hold  the  mercury  without  expansion.  In  the  middle  of  the  meas- 
uring tube  A  is  a  bulb  of  70  cubic  centimeters  capacity.  Above 
and  below  the. bulb  the  tube  is  divided  into  tenths  of  a  cubic  cen- 
timeter, and  its  diameter  is  such,  viz.,  11.3  millimeters,  that  each 
cubic  centimeter  occupies  a  length  of  one  centimeter.  The  upper 


Fig.  29.    Lunge's  Improved  Apparatus. 

end  of  A  is  closed  with  a  glass  cock  with  two  oblique  perforations, 
by  means  of  which  communication  can  be  established  at  will, 
either  through  e  with  the  apparatus  for  generating  the  gas,  or 
through  d,  with  the  absorption  apparatus,  or  the  opening  be  com- 
pletely closed. 

The  volume  of  air  under  the  observed  conditions,  which  would 


41  8  AGRICULTURAL  ANALYSIS 

measure  exactly  100  cubic  centimeters  at  o°  and  760  millimeters 
pressure  of  mercury,  is  calculated  by  the  formula 

_  IPO  (273  +  Q  760 


273 

where  t  equals  observed  temperature,  b  the  barometric  pressure 
less  the  correction  noted  below,  and  f  the  tension  of  the  vapor  of 
water  under  existing  conditions.  For  example  : 

Temperature  ...............................  18° 

Barometric  reading  .....    ..................  755 

Correction  for  b  ............................  2 

Corrected  barometer  .......................  753 

Vapor  of  water  tension  .....................  16 


Then  V  -  I0°  (27,3  +  I8)          =  109.9- 
273  (753—16) 

This  indicates  that  109.9  cubic  centimeters  of  air  would  occupy 
a  volume  of  100  cubic  centimeters  when  subjected  to  standard 
conditions. 

The  tubes  A,  B,  and  C,  are  filled  with  mercury  of  which  about 
two  and  a  half  kilograms  will  be  required.  By  means  of  the 
leveling  tube  B,  the  stopper  in  C  being  opened,  the  mercury  in 
C  is  brought  exactly  to  109.9  cubic  centimeters.  The  stopper 
in  C  is  then  closed,  mercury  poured  into  D,  which  is  then  closed 
with  a  rubber  stopper,  carrying  a  small  glass  tube,  as  indicated 
in  the  figure. 

The  leveling  tube  B  serves  to  regulate  the  pressure  on  the 
gas  in  A,  and  this  is  secured  by  depressing  or  elevating  it,  as  the 
case  may  require. 

The  tube  for  reducing  the  volume  to  standard  conditions  of 
temperature  and  pressure,  viz.,  o°  and  760  millimeters  of  mer- 
cury, is  shown  in  C.  In  its  narrow  part,  which  has  the  same  in- 
ternal diameter  as  A,  it  is  graduated  into  tenths  of  a  cubic  centi- 
meter. The  upper  end  of  C  is  furnished  with  a  heavy  glass  neck 
D,  surmounted  by  a  glass  cup.  In  the  neck  is  placed  a  ground- 
glass  stopper,  carrying  a  groove  below,  which  corresponds  to  a 
similar  groove  above  in  the  side  of  the  neck,  whereby  communica- 
tion can  be  established  at  will  between  the  interior  of  C  and  the 
exterior.  The  joint  is  also  sealed  by  pouring  mercury  into  D,  as 


METHOD  OF   MANIPULATION  419 

is  shown  in  the  figure.  When  the  stopper  is  well  ground  and 
greased  the  reduction  tube  may  be  raised  or  lowered  as  much  as 
may  be  necessary  without  any  danger  of  escape  or  entrance  of 
gas.  To  determine  the  position  of  the  reduction  tube  C  the 
reading  of  the  barometer  and  thermometer  at  room  temperature 
is  taken.  From  the  reading  of  the  barometer  subtract  one  milli- 
meter if  the  temperature  be  below  12°,  two  millimeters  at  a 
temperature  from  12°  to  19°,  three  from  20°  to  25°,  and  four 
above  25°. 

When  a  gas  has  been  introduced  into  the  measuring  tube  A 
ir  is  brought  to  the  volume  which  it  would  assume  under  stand- 
ard conditions  by  adjusting  the  tube  C,  in  such  a  way  as  to  bring 
the  mercury  in  C  and  A  to  the  same  height  and  the  surface 
of  the  mercury  in  C  is  exactly  at  100  cubic  centimeters.  The 
gas  in  A  is  then  at  the  volume  which  it  would  occupy  under 
standard  conditions,  and  this  volume  can  be  directly  read.  This 
adjustment  is  secured  by  moving  the  tubes  B  and  C  up  or  down. 
If  gases  are  to  be  measured  wet,  a  drop  of  water  should  be  put 
on  the  side  of  the  upper  part  of  C,  and  if  dry,  of  sulfuric  acid, 
before  the  adjustment  for  temperature  and  pressure. 

363.  Method  of  Manipulation. — By  the  action  of  mercury  in 
the  presence  of  sulfuric  acid,  the  nitrogen  in  nitrates,  nitrites, 
nitrosulfates,  nitroses,  nitrocellulose,  nitroglycerol,  and  the  greater 
number  of  explosives,  may  be  obtained  and  measured  as  nitric 
oxid.  The  nitrogen  compounds  are  decomposed  in  the  apparatus 
shown  in  Fig.  30. 

To  make  an  analysis,  the  apparatus  is  filled  with  mercury, 
through  F,  until  the  two  openings  in  the  cock  and  i  are  entirely 
occupied  with  that  liquid.  The  cock  h  is  then  closed,  and  the 
nitrogen  compound,  in  solution,  introduced  through  g,  care  being 
taken  that  no  air  enters  g  when  F  is  depressed  and  h  opened  to 
admit  the  sample.  The  funnel  g  is  washed  several  times  with  a 
few  drops  of  sulfuric  acid,  which  are  successively  introduced  into 
G.  The  total  liquid  introduced  should  not  exceed  10  or  15  cubic 
centimeters,  of  which  the  greater  part  should  be  sulfuric  acid. 
The  rubber  tube  connecting  G  and  F  is  carefully  closed  with  a 
clamp  and  G  violently  shaken  for  a  few  minutes  until  no  further 


420 


AGRICULTURAL  ANALYSIS 


evolution  of  nitric  oxid  takes  place.  In  shaking,  the  apparatus 
should  be  so  held  as  to  prevent  the  escape  of  the  mercury  from 
the  small  tube  i  by  keeping  it  closed  with  the  finger  or  drawing 
over  it  a  rubber  cap. 

After  the  evolution  of  the  gas  has  ceased,  the  tube  e,  Fig.  29, 
is  brought  into  contact  with  «',  (Fig.  30)  and  the  two  are  joined 
by  a  tight-fitting  piece  of  rubber  tubing  in  such  a  way  as  to  ex- 
clude any  particle  of  air.  The  tube  F,  Fig.  30,  is  lifted  and  B 
and  C,  Fig.  29,  depressed.  On  carefully  opening  the  cocks  h  and 
b,  and  bringing  i  and  e  into  union,  the  gas  is  passed  from  G  into 
A.  When  all  the  gasr'-ims  entered  A  and  the  acid  mixture  from 


Pig.  30.    I«unge's  Analytic  Apparatus. 

G  has  reached  b,  the  latter  is  closed,  and  also  h.  The  apparatus 
G  is  disconnected  and  removed.  The  gas  in  A  is  then  reduced  to 
normal  conditions  by  manipulating  the  reduction  tube,  C,  in  the 
manner  already  described. 

The  gas  in  A  is  measured  dry  by  reason  of  having  been  gen- 
erated in  presence  of  rather  strong  sulfuric  acid.  Consequently, 
for  this  operation  the  adjustment  of  the  volume'  of  gas  in  C 
should  be  made  in  contact  with  a  drop  of  strong  sulfuric  acid. 
In  order  to  make  the  readings,  a  quantity  of  material  must  be 


N?O3  in 
milligrams. 

HNO3  in 
milligrams. 

NaNO3  in 
milligrams. 

I.70I 

2.820 

3.805 

3.402 

5.640 

7.6lO 

5-103 

8.460 

11.415 

6.804 

II.280 

15.220 

8.506 

14.100 

19.025 

I0.2o6 

16.920 

22.830 

11.907 

19.740 

26.635 

13-608 

22.560 

30.440 

I5-309 

25-380 

34-245 

VOLUMETRIC   METHOD  OF  GANTTER  421 

taken  which  will  give  not  less  than  30  and  not  more  than  140 
cubic  centimeters  of  nitric  oxid. 

The  quantities  of  the  different  compounds  of  nitric  acid  cor- 
responding to  the  number  of  cubic  centimeters  of  nitric  oxid, 
measured  under  standard  conditions,  are  shown  in  the  following 
table : 

Corresponding  to 

Cubic  centimeters  Weight  in 
of  NO.  milligrams. 

* 1-343 

2 2.682 

3 4-029 

4 5-372 

5 6.715 

6 8.058 

7 9-401 

8 10.744 

9 12.087 

364.  Utility  of  the  Method. — Where  it  is  desirable  that  the 
nitric  oxid  method  be  used,  and  at  the  same  time  heating  be 
avoided,  the  decomposition  of  a  nitrate  by  means   of  metallic 
mercury  and  sulfuric  acid  affords  a  convenient  and  accurate  pro- 
cedure.    But,  as  a  rule,  there  is  no  objection  to  the  application 
of  the  lamp  except  in  the  case  of  explosives,  and  in  such  cases  the 
mercury  method  appears  to  have  no  advantage  over  the  ferrous 
chlorid  process.     Nevertheless,  in  the  hands  of  a  skilled  worker, 
the  results  are  reliable,  and  the  process  is  a  quicker  one,  on  the 
whole,  than  by  distillation  with  ferrous  chlorid  and  hydrochloric 
acid. 

365.  Volumetric   Method   of   Gantter. — The   process   proposed 
by  Gantter  for  determining  the  nitrogen  volumetrically  in  Chile 
saltpeter  and  other  nitrates  is  based  on  the  following  principles  :51 

(1)  If  a  nitrate  be  heated  in  contact  with  sulfuric  and  phos- 
phorous acids,  nitrous  and  phosphoric  acids  will  be  formed. 

(2)  If  nitrous  acid  be  boiled  with  ammonium  chlorid,  nitrogen 
will  be  quantitatively  evolved  from  both  compounds.    These  pro- 
cesses are  illustrated  by  the  following  formulas: 

(a)  N205+P203=N203+P206. 

(b)  N2O3+2NH4Cl-2N2+3H2O-f2HCl. 

51  Zeitschrift  fur  analytische  Chemie,  1895,  34  :  26. 


422 


AGRICULTURAL  ANALYSIS 


It  is  seen  from  the  above  that  the  nitrate  will  give,  by  this 
treatment,  double  the  volume  of  nitrogen  which  it  contains.  In 
practice,  the  two  reactions  may  be  secured  in  one  operation  by 
warming  the  nitrate  solution  slowly  with  sulfuric  and  phos- 
phorous acids  and  ammonium  chlorid.  The  nitric  acid,  as  it  be- 
comes free,  gives  a  part  of  its  oxygen  to  the  phosphorous  com- 
pound, and  the  nitrous  acid,  in  a  nascent  state,  is  at  once  reduced 
by  the  ammonium  chlorid.  There  are  two  sources  of  error  which 
must  be  guarded  against  in  the  work ;  a  portion  of  the  nitrogen 
may  escape  reduction  to  the  elementary  state,  or  some  of  the 
nitrate  may  fail  to  be  decomposed.  These  errors  are  easily 


Fig.  31.     Gantter's  Nitrogen  Apparatus. 

avoided  if  the  reaction  be  begun  slowly,  so  that  the  evolution  of 
gas  may  be  gradual.  The  temperatures  at  first  should,  therefore, 
be  kept  as  low  as  possible.  The  development  of  red  fumes,  show- 
ing the  presence  of  undecomposed  nitrogen  oxids,  shows  that 
the  results  will  be  too  low.  It  is  necessary,  also,  to  provide  for 
the  absorption  of  the  hydrochloric  acid  which  is  formed.  The 
reaction  is  very  conveniently  conducted  in  the  apparatus  shown 
in  Fig.  31.  The  decomposition  takes  place  in  the  flask  A,  and 
the  mixed  gases  pass  into  the  absorption  bulb  C.  The  delivery 
tube  is  very  much  expanded,  as  shown  in  the  figure,  so  that  no 
soda-lye  can  enter  A  during  the  cooling  of  the  flask.  The  absorp- 


VOLUMETRIC   METHOD  OF  GANTTER  423 

tion  bulb  is  connected  with  A  and  B  by  the  tubes  a  and  b,  as 
shown.  The  tube  d  connects  the  apparatus  with  the  gasvolu- 
meter.52  The  bulb  B  serves  as  a  pipette  for  the  introduction 
of  the  decomposing  acid.  The  operation  is  conducted  as  follows : 
Three  cubic  centimeters  of  the  nitrate  solution,  containing  no 
more  than  300  milligrams  of  the  substance,  are  placed  in  the 
flask  A,  with  half  a  gram  each  of  crystallized  ammonium  chlorid 
and  phosphorous  acid.  In  the  bulb  B  are  placed  seven  cubic  cen- 
timeters of  sulfuric  acid,  to  which  has  been  added  one-third  its 
volume  of  water.  Two  cubic  centimeters  of  acid  are  allowed  to 
flow  from  B  into  A.  The  apparatus  is  brought  to  a  constant 
temperature  by  being  immersed  in  a  large  cylinder  E,  containing 
water  at  a  temperature  which  can  easily  be  controlled.  When 
this  constant  temperature  has  been  reached  the  apparatus  is  taken 
from  the  cooling  cylinder,  which  contains  also  a  smaller  cylinder 
D,  nearly  filled  with  water  and  connected  through  f  with  the 
measuring  apparatus  M.  The  barometer-tube  F  is  half  filled 
with  colored  water,  so  that  the  pressure  may  be  equalized  before 
and  after  the  operation.  The  flask  A  is  warmed  very  gently  at 
first,  and  the  nitrogen  evolved  is  conducted  into  D,  driving  an 
equivalent  volume  of  water  into  M.  The  evolution  of  the  gas 
must  be  carefully  controlled  and  the  heat  at  once  removed  if  it 
becomes  too  rapid.  The  appearance  of  a  red  color  shows  the 
evolution  of  oxids  of  nitrogen,  rendering  the  analysis  inexact. 
When  the  evolution  of  nitrogen  has  nearly  ceased,  the  lamp  is 
removed  and  some  more  sulfuric  acid  allowed  to  flow  into  A 
from  B,  after  which  A  is  again  heated,  this  time  to  the  boiling- 
point.  All  vapors  of  hydrochloric  acid  produced  are  absorbed 
by  the  soda-lye  in  C.  The  boiling  is  continued  a  few  minutes, 
but  not  long  enough  to  darken  the  liquid  in  A.  After  replacing  the 
apparatus  in  the  cylinder  E,  and  bringing  both  temperature  and 
pressure  to  the  same  point  as  before  the  beginning  of  the  opera- 
tion, the  volume  of  nitrogen  evolved  is  determined  by  measuring 
the  water  ki  M. 

The  apparatus  is  first  set  by  using  pure  potassium  or  sodium 
nitrate.     Since  the  temperature  and  pressure  do  not  vary  much 
M  Zeitschrift  fur  analytische  Chemie,  1893,  32  :  553- 


424  AGRICULTURAL  ANALYSIS 

within  an  hour  or  two,  the  volume  of  water  obtained  with  a  sam- 
ple of  Chile  saltpeter  can  be  compared  directly  with  that  given 
oft"  by  the  same  weight  of  a  pure  potassium  or  sodium  nitrate 
without  correction. 

Example. — Two  hundred  and  fifty  milligrams  of  potassium 
nitrate,  containing  34.625  milligrams  of  nitrogen,  displaced  in  a 
given  case  60  cubic  centimeters  of  water ;  therefore,  one  cubic 
centimeter  of  water  equals  0.578  milligram  of  niirogen.  If  289 
instead  of  250  milligrams  be  taken,  then  the  number  of  cubic  cen- 
timeters of  water  displaced  divided  by  five  will  give  the  per  cent, 
of  nitrogen. 

366.  Method  of  Difference. — In  the  analysis  of  Chile  salt- 
peter by  the  direct  method  a  variation  of  0.25  per  cent,  in  the 
content  of  nitrogen  is  allowed  from  the  dealers'  guaranty.  This 
would  allow  a  total  variation  in  the  content  of  sodium  nitrate 
of  1.52  per  cent.  Dealers  and  shippers  have  always  been  accus- 
tomed to  estimate  the  quantity  of  sodium  nitrate  in  a  sample  by 
difference ;  i.  e.,  by  estimating  the  constituents  not  sodium  nitrate 
and  subtracting  the  sum  of  the  results  from  100.  Chile  saltpeter 
usually  contains  sodium  nitrate,  water,  insoluble  ferruginous  mat- 
ters, sodium  chlorid,  sodium  sulfate,  magnesium  chlorid,  sodium 
iodate,  calcium  sulfate  and  sometimes  small  quantities  of  potas- 
sium nitrate. 

When  the  total  sodium  nitrate  is  to  be  estimated  by  difference, 
the  following  procedure,  suggested  by  Crispo,  may  be  followed  :53 

Water. — Dry  10  grams  of  the  finely  powdered  sample  to  con- 
stant weight  at  i5O°-i6o°. 

Chlorin. — The  residue,  after  drying,  is  dissolved  and  the  vol- 
ume made  up  to  one-fourth  liter  with  water  and  the  chlorin  de- 
termined in  one-fifth  thereof  and  calculated  as  sodium  chlorid. 

Insoluble. — Twenty  grams  are  treated  with  water  until  all  solu- 
ble matter  has  disappeared,  filtered  on  a  tared  gooch,  and  the 
crucible  dried  to  constant  weight. 

Sulfuric  Acid. — The  sulfuric   acid  is  precipitated  by  barium 
chlorid  in  the  slightly   acid  filtrate   from  the  insoluble  matter. 
M  L'Engrais,  1894,  9  :  877. 


PRINCIPLES  OF   THE    METHOD  425 

The  acidity  is  produced  by  a  few  drops  of  nitric  acid.  The  rest 
of  the  process  is  conducted  in  the  usual  way. 

Magnesia. — This  is  precipitated  by  ammonium  sodium  phos- 
phate, filtered,  ignited,  and  weighed  as  pyrophosphate.  The  mag- 
nesia is  then  calculated  as  chlorid.  Magnesia  is  rarely  found 
in  excess  of  one-fourth  per  cent.  When  this  amount  is  not  ex- 
ceeded the  estimation  of  it  may  be  neglected  without  any  great 
error.  As  has  already  been  said,  the  chlorin  is  all  calculated  as 
sodium  chlorid.  If  a  part  of  it  be  combined  with  one-fourth 
per  cent,  of  magnesia,  it  would  represent  0.59  per  cent,  of  mag- 
nesium chlorid  instead  of  0.73  per  cent,  sodium  chlorid.  In 
omitting  the  estimation  of  the  magnesia,  therefore,  the  importer 
is  only  damaged  to  the  extent  of  0.14  per  cent,  of  sodium  nitrate. 

Sodium  lodate. — This  body,  present  only  in  small  quantities, 
may  also  be  neglected.  In  case  the  content  of  this  body  should 
reach  one-fourth  per  cent,  the  estimation  of  chlorin  by  titration, 
using  potassium  chromate  as  indicator,  is  impracticable.  Such  an 
instance,  however,  is  rarely  known. 

Approximate  Results. — When  the  determinations  outlined  above 
have  been  carefully  made,  it  is  claimed  that  the  result  obtained 
by  subtraction  from  100  will  not  vary  more  than  from  two-tenths 
to  three-tenths  per  cent,  from  the  true  content  of  sodium  nitrate. 
The  method,  however,  cannot  be  considered  strictly  scientific  and 
is  much  more  tedious  and  chronophagous  than  the  direct  deter- 
mination. In  the  direct  determination,  however,  the  analyst  must 
assure  himself  that  potassium  is  present  in  only  appreciable  quan- 
tities, otherwise  the  per  cent,  of  sodium  nitrate  will  be  too  low. 

The  presence  of  potassium  nitrate  is  a  detriment  in  this  re- 
spect only;  viz.,  that  it  contains  a  less  percentage  of  nitrogen 
than  the  corresponding  sodium  salt.  As  a  fertilizer,  the  value 
of  Chile  saltpeter  may  be  increased  by  its  content  of  potassium. 

ESTIMATION  OF  NITRIC  ACID  BY  OXIDATION  OF  A 
COLORED  SOLUTION 

367.  Principles  of  the  Method. — Solutions  of  organic  coloring 
matter  in  certain  conditions  are  decolorized  by  nitric  acid.  The 
process  is  one  of  oxidation  and  the  disappearance  of  the  natural 


426  AGRICULTURAL  ANALYSIS 

color  marks  the  end  of  the  reaction.     Indigo  is  the  only  coloring 
matter  that  has  been  used  to  any  extent  in  this  process. 

368.  Method  of  Marx. — The  indigo  method  as  usually  practiced 
is  conducted  according  to  the  principle  described  by  Marx.5* 
There  are  required  for  the  process  the  following  reagents  and 
apparatus : 

a.  A  solution  of  pure  potassium  nitrate  containing  i  .8724  grams 
per  liter.     One  cubic  centimeter  of  the  solution  is  equivalent  to  one 
milligram  of  nitric  anhydrid  (N2O5). 

b.  A  solution  of  the  best  indigo  carmine  in  water,  which  should 
be  approximately  standardized  by  solution  in  the  manner  described 
hereafter,  and  then  diluted  so  that  from  six  to  eight  cubic  centi- 
meters equal  one  milligram  of  nitric  acid. 

c.  Chemically  pure  sulfuric  acid  of  specific  gravity  1.842,  per- 
fectly free  from  sulfurous  and  arsenious  acids  and  nitrogen  oxids. 

d.  Several  thin  flasks  of  about  200  cubic  centimeters  capacity. 

e.  A  small  cylindrical  measure  holding  50  cubic  centimeters 
and  divided  into  cubic  centimeters. 

/.  A  Mohr's  burette  divided  into  tenths  of  a  cubic  centimeter. 

g.  A  25  cubic  centimeter  pipette  or  another  burette. 

h.  A  five  cubic  centimeter  pipette  divided  into  cubic  centime- 
ters or  half  cubic  centimeters. 

i.  A  measuring  flask  of  250  cubic  centimeters  capacity. 

Preliminary  Trial. — Twenty-five  cubic  centimeters  of  the  sam- 
ple are  transferred  to  a  flask;  the  50  cubic  centimeter  measure 
is  filled  with  sulfuric  acid  and  the  burette  with  indigo  solution. 
The  sulfuric  acid  is  added  to  the  sample  all  at  once,  shaken  for 
a  moment,  and  the  indigo  run  in  as  quickly  as  possible  with 
shaking  until  a  permanent  greenish  tint  is  produced.  If  the 
sample  does  not  require  more  than  20  cubic  centimeters  of  indigo 
solution  of  the  above  strength,  it  can  be  titrated  directly,  other- 
wise it  must  be  diluted  with  a  proper  quantity  of  pure  water, 
and  subjected  again  to  the  preliminary  trial. 

The  Actual  Titration. —  (i)  Twenty-five  cubic  centimeters  of 
the  sample,  properly  diluted  if  necessary,  are  poured  into  a  flask, 
and  as  much  indigo  as  was  used  in  the  preliminary  trial  is  added ; 
54  Zeitschrift  fur  analytische  Chemie,  1868,  7  :  412. 


METHOD  OF  BOUSSINGAULT  427 

a  quantity  of  sulfuric  acid,  equal  in  volume  to  the  liquid  in  the 
flask,  is  added  all  at  once,  the  mixture  shaken,  and  indigo  solu- 
tion run  in  quickly  out  of  the  burette  until  the  liquid  remains  per- 
manently of  a  greenish  tint. 

(2)  The  last  experiment  is  repeated  as  often  as  may  be  neces- 
sary, adding  to  the  water  at  first  half  a  cubic  centimeter  less 
indigo  than  the  total  quantity  used  previously,  afterwards  pro- 
ceeding as  in  ( i )  until  the  final  test  shows  too  little  indigo  used. 

(3)  From   the    rough   titration   of   the   indigo,   calculate   the 
amount  of  potassium  nitrate  solution  corresponding  with  the  in- 
digo solution  used  in  (2),  multiply  the  result  by  10,  transfer  this 
quantity  of  the  standard  nitrate  solution  to  a  250  cubic  centime- 
ter flask,  fill  with  pure  water  to  the  mark,  and  titrate  25  cubic 
centimeters  of  this  fluid  with  indigo  as  in  (2).     If  the  quantity 
of  indigo  solution  used  is  nearly  the  same  as  that  required  in  (2), 
its  exact  value  may  be  calculated,  but  if  it  is  not,  another  nitrate 
solution  may  be  made  up  in  the  250  cubic  centimeter  flask,  more 
closely  resembling  the  sample  in  strength,  and  the  titration  with 
the  indigo  solution  must  be  repeated. 

(4)  If  the  water  contains  any  considerable  amount  of  organic 
matter,  it  must  first  be  destroyed  by  potassium  permanganate. 
In  this  case,  the  estimation  of  the  organic  matter  and  nitric  acid 
may  be  conveniently  combined. 

The  use  of  permanganate  in  the  above  case  is  likely  to  intro- 
duce an  error  as  has  been  shown  by  Warington.  The  method, 
therefore,  can  not  be  recommended  in  the  presence  of  organic 
matter. 

369.  Method  of  Boussingault. — The  process  for  the  estima- 
tion of  nitric  acid  by  the  decoloration  of  a  solution  of  indigo  is 
due  originally  to  Boussingault.55  In  this  method  the  extract,  ob- 
tained by  washing  slowly  200  grams  of  soil  until  the  filtrate 
amounts  to  300  cubic  centimeters,  is  evaporated  until  its  volume 
is  no  greater  than  two  or  three  cubic  centimeters,  and  it  is  trans- 
ferred to  a  test-tube,  with  washings,  and  again  evaporated  in  the 
tube  until  the  volume  is  not  greater  than  that  last  mentioned.  A 
few  drops  of  solution  of  indigo  are  added,  and  then  two  cubic 
55  Encyclopedic  chimique,  1888,  4  :  154- 


428  AGRICULTURAL  ANALYSIS 

centimeters  of  pure  hydrochloric  acid;  the  whole  is  then  heated. 
As  the  color  of  the  indigo  disappears  more  is  added.  When  the 
color  ceases  to  fade,  the  liquid  in  the  test-tube  is  concentrated 
by  boiling.  If  concentration  fail  to  destroy  the  blue  or  green 
color,  another  one-half  cubic  centimeter  of  hydrochloric  acid  is 
introduced.  The  reaction  is  completed  when  neither  concentra- 
tion nor  fresh  addition  of  hydrochloric  acid  destroys  the  excess 
of  indigo  present.  The  color  produced  by  a  small  excess  of  in- 
digo is  a  bright  green ;  this  tint  is  the  final  reaction  sought.  The 
small  excess  of  indigo  necessary  to  produce  a  green  color  is  de- 
ducted in  every  experiment. 

When  more  than  mere  traces  of  organic  matter  are  present, 
Boussingault  advises  that  the  nitric  acid  be  first  separated  by 
distillation  and  then  reduced  by  the  indigo  solution.  For  this 
purpose  the  concentrated  solution  of  the  nitrate,  two  or  three 
cubic  centimeters,  is  placed  in  a  small  tubulated  retort  with  two 
grams  of  manganese  dioxid  in  fine  powder.  The  retort  is  next 
half  filled  with  fragments  of  broken  glass,  over  which  is  poured 
one  cubic  centimeter  of  concentrated  sulfuric  acid.  The  retort 
is  heated  carefully  by  means  of  a  small  flame,  which  is  kept  in 
motion  so  as  to  successively  come  in  contact  with  all  parts  of 
the  bottom  of  the  retort.  The  distillate  is  received  in  a  graduated 
test-tube  which  is  kept  cool.  The  distillation  is  continued  until 
the  vapors  of  sulfuric  acid  begin  to  appear.  The  apparatus  is 
allowed  to  cool,  the  stopper  of  the  retort  removed,  two  cubic  cen- 
timeters of  water  introduced,  and  the  distillation  repeated  until 
fumes  of  sulfuric  acid  are  again  seen.  The  distillation  with  water 
is  made  twice  in  order  to  remove  every  trace  of  nitric  acid  from 
the  retort.  The  distillate  is  neutralized  with  a  solution  of  potas- 
sium hydroxid  and  concentrated  to  two  cubic  centimeters,  and 
the  nitric  acid  estimated  in  the  manner  already  described.  The 
manganese  dioxid  used  should  be  previously  well  washed  and 
the  sulfuric  must  be  free  of  nitric  acid. 

Preparation  of  the  Indigo  Solution. — Fifty  grams  of.  indigo,  in 
fine  powder  are  digested  for  24  hours  at  40°  in  a  liter  of  distilled 
water.  The  water  is  poured  off  and  replaced  with  a  fresh  sup- 


METHOD    OF    WARINGTON  429 

ply.  After  the  second  decantation  the  residue  is  treated  with 
750  cubic  centimeters  of  equal  parts  of  water  and  pure  concen- 
trated hydrochloric  acid  and  boiled  for  an  hour.  After  cooling, 
the  undissolved  portion  is  collected  on  a  filter  and  washed  at  first 
with  hot,  and  afterwards  with  cold  water,  until  the  filtrate  is  no 
longer  colored  and  is  free  of  acid.  The  dried  residue  is  treated 
with  ether  under  a  bell-jar,  or  in  a  continuous  extraction  appara- 
tus until  the  ether  is  only  of  a  faint  blue  tint.  The  50  grams  of 
indigo  will  yield  about  25  grams  of  the  purified  article,  which, 
however,  will  still  leave  a  little  ash  on  combustion. 

Solution  in  Sulfuric  Acid. — Five  grams  of  the  purified  indigo 
are  placed  in  a  flask  having  a  ground-glass  stopper,  treated  with 
25  grams  of  fuming  sulfuric  acid,  and  allowed  to  digest  two  or 
three  days  at  a  temperature  of  from  50°  to  60°.  From  70  to 
200  drops  of  the  solution  thus  made  are  placed  in  100  cubic  centi- 
meters of  water  for  use  in  the  process. 

Standardization  of  the  Indigo  Solution, — The  solution  as  pre- 
pared above  is  standardized  by  a  solution  of  one  gram  of  pure 
potassium  nitrate  in  1000  cubic  centimeters  of  distilled  water. 
The  oxidation  of  the  indigo  solution  is  accomplished  as  described 
above.  Of  this  strength  of  standard  nitrate  solution  two  cubic 
centimeters  are  used,  corresponding  to  two  milligrams  of  potas- 
sium nitrate.  The  indigo  solution  for  this  strength  potassium 
nitrate  solution  should  have  only  20  drops  of  the  sulfuric  acid 
solution  of  indigo  to  ioo  cubic  centimeters  of  water.  If  20  grams 
of  potassium  nitrate  are  used  for  1000  cubic  centimeters  of  the 
standard  solution,  then  200  drops  of  the  sulfindigotic  acid  should 
be  used  to  ioo  cubic  centimeters  of  water. 

370.  Method  of  Warington. — The  modification  of  the  indigo 
method  as  used  by  Warington,  applicable  only  in  absence  of 
organic  matter,  is  the  one  chiefly  employed  in  England.56 

Instead  of  the  ordinary  indigo  of  commerce,  indigotin  is  used. 
The  normal  solution  of  the  coloring  matter  is  made  of  such  a 
strength  as  to  be  equivalent  to  a  solution  of  potassium  nitrate 
containing  0.14  gram  of  nitrogen  per  liter.  When  large  quan- 
tities of  the  coloring  matter  are  to  be  used,  it  is  advisable  to  pre- 
M  Journal  of  the  Chemical  Society,  1879,  36 •'.  5?8. 


43°  AGRICULTURAL  ANALYSIS 

pare  it  about  four  times  the  strength  given  above  and  then  dilute 
it  as  required.  Four  grams  of  sublimed  indigotin  will  furnish 
more  than  two  liters  of  the  color  solution. 

The  solution  is  prepared  as  follows : 

Four  grams  of  indigotin  are  digested  for  a  few  hours  with  five 
times  that  weight  of  Nordhausen  sulfuric  acid,  diluted  with  water, 
filtered  and  made  up  to  a  volume  of  two  liters.  The  strength 
of  the  indigotin  solution  is  determined  with  a  solution  of  potas- 
sium nitrate  of  the  strength  mentioned  above.  The  process  is 
performed  as  follows: 

From  10  to  20  cubic  centimeters  of  the  standard  nitrate  solution 
are  placed  in  a  wide-mouthed  flask  of  about  150  cubic  centimeters 
capacity.  A  portion  of  the  indigotin  solution  is  added,  such  as 
will  be  deemed  sufficient  for  the  process,  and  the  whole  is  well 
mixed.  Strong  sulfuric  acid  is  measured  from  a  burette  into  a 
test-tube,  in  volume  equal  to  the  united  volumes  of  the  nitrate  solu- 
tion and  indigotin.  The  whole  of  the  sulfuric  acid  is  then  poured, 
as  quickly  as  possible,  into  the  solution  in  the  flask  and  rapidly 
mixed,  and  the  flask  transferred  to  a  calcium  chlorid  bath,  the 
temperature  of  which  should  be  maintained  at  140°.  It  is  essen- 
tial to  the  success  of  the  operation  that  the  sulfuric  acid  should 
be  mixed  with  the  greatest  rapidity.  It  is  poured  in  at  once  and 
the  whole  well  shaken  without  waiting  for  the  test-tube,  contain- 
ing the  acid,  to  drain.  The  flask  is  covered  with  a  watch-glass 
while  it  is  held  in  the  bath.  As  soon  as  the  larger  part  of  the 
indigotin  is  oxidized  the  flask  in  the  bath  is  gently  rotated.  With 
very  weak  solutions  of  nitrate  it  may  be  necessary  sometimes  to 
keep  the  flask  in  the  bath  for  five  minutes.  When  the  indigo 
color  is  quickly  discharged,  it  shows  the  presence  of  nitric  acid 
in  considerable  excess  and  a  larger  quantity  of  indigo  must  be 
used  in  the  next  experiment.  The  experiments  are  continued  un- 
til just  the  quantity  of  indigotin  necessary  to  consume  the  nitric 
acid  is  found,  the  amount  of  indigotin  being  in  very  slight  excess, 
not  exceeding  one-tenth  cubic  centimeter  of  the  indigotin  solution 
used.  The  tint  produced  by  the  small  excess  of  indigotin  re- 
maining is  best  seen  by  filling  the  flask  with  water.  On  substances 
of  approximately  known  strength  about  four  experiments  are 


METHOD    OF    WARINGTON 


431 


usually  necessary  to  determine  the  proper  amount  of  indigotin, 
but  with  unknown  substances  a  larger  number  may  be  necessary. 

Usually  in  determinations  of  this  kind  it  is  directed  to  use 
double  the  volume  of  sulfuric  acid  mentioned  above.  In  this 
case  not  only  is  the  quantity  of  indigotin  oxidized  much  greater 
than  with  a  smaller  portion  of  acid,  but  the  prejudicial  effect  of 
organic  matter  is  also  greater  when  the  smaller  quantity  of  acid 
is  employed. 

An  indigotin  solution  standardized  as  above  is  strictly  to  be  used 
for  a  solution  of  nitrate  of  the  strength  employed  during  the  stan- 
dardization. The  quantity  of  indigotin  oxidized  in  proportion 
to  the  nitric  acid  present  diminishes  as  the  nitrate  solution 
becomes  more  dilute.  Instead  of  determining  this  during  each 
series  of  experiments  it  may  be  estimated  once  for  all  and  a  table 
of  corrections  used. 

The  following  table  is  based  upon  experimental  determinations : 


Difference  in  the 
nitrogen  value 

Difference        Nitrogen 

for  a  difference 

Strength 

between     corresponding 

Difference 

of  one  cubic 

of  niter 

amounts     to  one  cubic 

between 

centimeter  in 

solution 
used. 

Indigotin 
required, 

of  indigo-      centimeter 
tin,        of  indigotin, 

the  nitrogen 
values. 

the  amount 
of  indigotin. 

cc. 

cc.                gram. 

gram. 

gram. 

S     ^J/itrn  A  1 

TO  rw~i 

....          O.OOOO^SOOO 

r    i.^t  Ul  liiai  • 

•  .  •           1  u,  ^_HJ 

...          8.7I 

1.29       0.000035161 

O.OOOOOOl6l 

0.000000125 

'T        "     • 

•  •  •       7-43 

1.28       0.000035330 

0.000000169 

0.000000132 

V        "     • 

6.14 

1.29        0.000035627 

0.000000298 

0.000000231 

V      "    • 

4.86 

1.28        0.000036008 

0.000000381 

0.000000298 

?f        "     • 

•'•••       3-57 

1.29        0.000036763 

0.000000756 

0.000000586 

\        "     • 

2.29 

1.28        0.000038209 

O.OOOOOI445 

0.000001129 

"?        "     • 

I.OO 

1.29       0.000043750 

0.000005541 

0.000004295 

The  table  is  used  as  follows: 

Suppose  that  20  cubic  centimeters  of  water  under  examination 
have  required  5.36  cubic  centimeters  of  indigotin  solution  for 
the  oxidation  of  the  nitric  acid  contained  therein.  By  inspec- 
tion of  the  table  it  is  seen  that  this  number  is  five-tenths  cubic 
centimeter  above  the  nearest  quantity  given,  viz.,  4.86  cubic  centi- 
meters. From  the  last  column  in  the  tabie  it  is  found  that  the 
correction  for  five-tenths  cubic  centimeter  of  indigotin  solution 
is  0.000000149  cubic  centimeter,  being  half  that  for  the  one  cubic 
centimeter  given  in  the  table.  This  is  to  be  subtracted  from  the 


432  AGRICULTURAL  ANALYSIS 

unit  value  in  nitrogen  given  in  the  first  "gram"  column  of  the 
table ;  viz.,  0.000036008.  It  is  thus  seen  that  the  5.86  cubic  cen- 
timeters of  indigotin  solution  are  equivalent  to  0.000035859  gram 
of  nitrogen  per  cubic  centimeter.  The  water  under  examination, 
therefore,  contains  nine  and  six-tenths  parts  of  nitrogen  as  nitric 
acid  per  million. 

Attention  must  also  be  paid  in  standardizing  indigotin  solu- 
tions to  the  initial  temperature.  A  rise  in  the  initial  temperature 
will  be  attended  by  a  diminution  in  the  quantity  of  indigotin  oxi- 
dized. Experiments  with  a  room  temperature  of  10°  and  a 
room  temperature  of  20°,  being  the  initial  temperatures  of  the 
experiments,  showed  that  at  the  higher  temperature  the  amount 
of  indigotin  consumed  was  about  five  per  cent,  less  when  the 
strong  solutions  of  nitrate  were  employed.  The  indigotin  solution, 
therefore,  must  be  standardized  at  the  same  temperature  at  which 
the  determinations  are  made. 

If  20  cubic  centimeters  of  the  standard  nitrate  solution  em- 
ployed be  used  in  setting  the  indigotin  solution,  this  stand- 
ard will  enable  the  operator  to  determine  nitric  acid  up  to  17.5 
parts  of  nitrogen  per  million  in  water  or  soil  extracts. 

The  presence  of  an  abundance  of  chlorids  in  the  water  under 
examination  tends  to  diminish  the  content  of  nitric  acid  found, 
and  also  tends  to  introduce  an  error,  which  is  sometimes  of  a 
plus  and  sometimes  of  a  minus  quantity,  according  to  the  strength 
of  the  nitric  acid  present.  The  reaction  is  shortened  in  weak 
solutions  by  the  presence  of  chlorids,  and  the  quantity  of  indigotin 
consumed  is  consequently  increased.  The  error  introduced  by 
chlorids  is  usually  of  an  insignificant  nature. 

On  account  of  the  interference  of  organic  matters  with  the 
reaction  of  indigotin  it  is  not  of  much  use  in  the  examination  of 
nitrates  washed  out  of  soils,  although  in  some  cases  the  results 
may  be  quite  accurate.  This  method  must,  therefore,  be  con- 
sidered as  applicable,  in  general,  only  to  waters  or  soil  extracts 
which  contain  little  or  no  organic  matter. 

In  analytical  work  pertaining  particularly  to  agriculture,  the  use 
of  the  indigotin  method  for  determining  nitric  acid  has  been 
•largely  employed,  both  in  the  analyses  of  soil  extracts  and  drain- 


CLASSIFICATION  OF  METHODS  433 

age  and  irrigation  waters.  The  method,  however,  can  hardly  sur- 
vive as  an  important  one  in  such  work  in  competition  with  more 
modern,  speedy  and  equally  accurate  processes  of  analysis. 

DETERMINATION  OF    NITRIC   NITROGEN    BY   REDUCTION 

TO  AMMONIA 

371.  Classification  of  Methods. — When  nitrogen  is  present 
in  a  highly  oxidized  state,  e.  g.,  as  nitric  acid,  it  may  be  quickly 
and  accurately  estimated  by  reduction  to  ammonia.  This  action 
is  effected,  among  other  ways,  by  the  reducing  power  of  nascent 
hydrogen,  and  this  substance  may  be  secured  in  the  active  state 
by  the  action  of  an  acid  or  alkali  on  a  metal,  or  by  means  of  an 
electric  current.  The  processes  depending  on  the  use  of  a  finely 
divided  metal  in  the  presence  of  an  acid  or  alkali  have  come  into 
general  use  within  a  few  years,  and  are  now  employed  generally 
instead  of  the  more  elaborate  estimations  depending  on  the  com- 
bustion method  by  the  use  of  copper  oxid  or  in  the  colorimetric 
method  with  indigo. 

The  typical  reaction  which  takes  place  in  all  cases  is  repre- 
sented by  the  following  equation : 

2HNO3+8H2=2NH3+6H2O. 

The  method  will  be  considered  under  three  heads;  viz.,  i. 
Reduction  in  an  alkaline  solution ;  2.  Reduction  in  an  acid  solu- 
tion ;  3.  Reduction  by  means  of  an  electric  current. 

In  the  first  class  of  processes  the  reduction  and  distillation 
may  go  on  together.  In  the  second  class  the  reduction  is  accom- 
plished first  and  the  distillation  effected  afterwards,  with  the 
addition  of  an  alkali.  In  the  third  class  of  operations  the  reduc- 
tion is  accomplished  by  means  of  an  electric  current  and  the 
ammonia  subsequently  obtained  by  distillation,  or  determined  by 
nesslerizing.  These  processes  may  be  applied  to  the  nitrates  or 
nitrites  as  such,  or  as  occurring  in  rain  and  drainage  waters 
and  soil  extracts.  On  account  of  the  ease  with  which  the  analyses 
are  accomplished,  the  short  time  required  and  the  accuracy  of  the 
results,  the  reduction  methods  for  nitrates  have  already  com- 
mended themselves  to  analysts,  and  are  quite  likely  to  supersede  all 
others  for  practical  use  where  small  yet  wefghable  quantities  of 


434  AGRICULTURAL  ANALYSIS 

nitrates  are  present.  For  the  minute  traces  of  nitrates  found  in 
rain  and  drainage  waters,  and  in  some  soil  extracts,  the  reduction 
method  may  also  be  applied,  but  in  these  cases  the  ammonia  which 
is  formed  must  be  determined  colorimetrically  (nesslerizing)  and 
not  by  distillation.  The  processes  about  to  be  described  are 
especially  applicable  to  the  examination  of  fertilizers  containing 
only  small  quantities  of  nitrates  and  of  soils  and  waters  rich  in 
nitrates. 

REDUCTION  IN  ALKALINE  SOLUTIONS 

372.  Extraction  of  the  Nitrates. — Place  one  kilogram  of  the  dry 
soil  or  fertilizers  poor  in  nitrates,  calculated  to  water-free  sub- 
stance, on  a  percolator  of  glass  or  tin.     Moisten  the  soil  thor- 
oughly with  pure  distilled  water,  and  allow  to  stand  for  half  an 
hour.     Add  fresh  portions  of  pure  distilled  water  until  the  filtrate 
secured  amounts  to  one  liter.     If  the  first  filtrate  be  cloudy  before 
use  it  may  be  refiltered. 

373.  Qualitative  Test  for  Nitrates. — Evaporate  five  cubic  centi- 
meters of  the  extract  as  obtained  above  in  a  porcelain  crucible, 
having  first  dissolved  a  small  quantity  of  pure  brucin   sulfate 
therein.     When  dry,  add  to  the  residue  a  drop  of  concentrated  sul- 
furic  acid  free  of  nitrates.   If  the  nitrate  calculated  as  potassium 
nitrate  does  not  exceed  the  two-thousandth  part  of  a  milligram, 
only  a  pink  color  will  be  developed;  with  the  three-thousandth 
part  of  a  milligram,  a  pink  color  with  reddish  lines;  with  the 
four-thousandth  part  of  a  milligram,  a  reddish  color ;  with  the 
five-thousandth  part  of  a  milligram,  a  distinct  red  color. 

374.  Sodium-Mercury  Amalgam  Method. — The     reduction     is 
effected  by  means  of  hydrogen  evolved  by  the  action  of  a  prep- 
aration of  sodium  amalgam.       Place  100  cubic  centimeters  of 
mercury  in  a  flask  of  half  a  liter  capacity;  warm  until  paraffin 
will  remain  melted  over  the   surface;  drop  successively  in  the 
paraffin-covered  mercury  pieces  of  metallic  sodium  of  the  size  of 
a  pea  until  6.75  grams  have  united  with  the  mercury.     The  amal- 
gam thus  prepared  contains  0.5  per  cent,  of  metallic  sodium  and 
may  be  preserved  indefinitely  under  the  covering  of  paraffin. 

Estimation  of  the  Nitrates. — Evaporate  100  cubic  centimeters 


HALLE   ZINC-IRON    METHOD  435 

of  the  soil  extract  to  dryness  on  a  steam-bath.  Dissolve  the 
soluble  portions  of  the  residue  in  100  cubic  centimeters  of 
ammonia-free  distilled  water,  filtering  out  any  insoluble  residue. 
Place  the  solution  in  a  flask,  add  10  cubic  centimeters  of  sodium 
amalgam,  stopper  the  flask  with  a  valve  which  will  permit  the 
escape  of  hydrogen,  and  allow  to  stand  in  a  cool  room  for  24 
hours.  Add  50  cubic  centimeters  of  milk  of  lime  and  titrate 
the  ammonia  produced  by  distillation  with  standard  acid  and 
estimate  as  nitrogen  pentoxid.  Where  the  amount  of  ammonia 
is  small,  nesslerizing  may  be  substituted  for  titration. 

375.  Method    of    the    Experiment    Station    at    Mockern. — The 
principle  of  this  reaction  is  based  on  the  reducing  action  exercised 
by  nascent  hydrogen  on  a  nitrate,  the  hydrogen  being  generated 
by  the  action  of  soda-lye  on  a  mixture  of  zinc  dust  and  finely 
divided  iron.57 

Ten  grams  of  nitrate  are  dissolved  in  500  cubic  centimeters  of 
water.  Of  this  solution  25  cubic  centimeters,  corresponding 
to  one-half  gram,  are  placed  in  a  distillation  flask  of  about  400 
cubic  centimeters  capacity,  120  cubic  centimeters  of  water  added, 
and  about  five  grams  of  well  v.  ashed  and  dried  zinc  dust  and  an 
equal  weight  of  reduced  iron.  To  the  solution  are  added  80 
cubic  centimeters  of  soda-lye  of  32°  B.  The  flask  is  connected 
with  the  condensing  apparatus  and  the  distillation  carried  on 
synchronously  with  the  reduction,  the  ammonia  being  collected 
in  20  cubic  centimeters  of  titrated  sulfuric  acid.  The  distillation 
is  continued  from  one  to  two  hours,  or  until  100  cubic  centimeters 
have  been  distilled,  and  the  remaining  sulfuric  acid  is  titrated 
in  the  usual  way.  Soil  extracts  and  sewage  waters  should  be 
concentrated  until  they  have  approximately  the  proportion  of  ni- 
trates given  above. 

376.  The  Halle  Zinc-Iron  Method. — For  determining  the  nitro- 
gen  in   Chile   saltpeter  the   foregoing  method   is   conducted   at 
the  Halle  Station  as  follows  :58     Ten  grams  of  the  nitrate  are  dis- 
solved in  one  liter  and  50  cubic  centimeters  of  the  solution  cor- 

57  Bottcher,  Die  landwirtschaftlichen  Versuchs-Stationen,  1892,  41  :  165. 
48  Bieler    und    Schneidewind,     Die    agricultur-chemische      Versuchs- 
station,  Halle  a/S.,  1892  :  50. 


AGRICULTURAL  ANALYSIS 


responding  to  half  a  gram  of  the  sample,  used  for  each  deter- 
mination. The  apparatus  employed  is  shown  in  Fig.  32.  A 
mixture  of  five  grams  of  zinc  dust  and  an  equal  weight  of  iron 
filings  is  employed  as  the  source  of  hydrogen.  The  reduction 
takes  place  in  an  alkaline  medium  secured  by  adding  to  the 
other  materials  mentioned  80  cubic  centimeters  of  soda-lye  of 
1.30  specific  gravity.  The  respective  quantities  of  iron  and 
zinc  may  be  measured  instead  of  weighed,  as  exact  proportions 
are  not  required.  After  the  addition  of  all  the  materials  the 
flask  is  allowed  to  stand  for  an  hour  at  room  temperature.  The 
distillation  is  then  commenced  and  continued  until  at  least  100 
cubic  centimeters  of  distillate  have  been  collected.  The  receiv- 
ing flasks  are  ordinary  erlenmeyers,  each  of  which  contains  20 


Fig.  32.     Halle  Nitric  Acid  Apparatus. 

cubic  centimeters  of  set  sulfuric  acid,  as  in  the  usual  kjeldahl 
process.  The  receiving  flasks  are  sealed  with  a  few  drops  of 
water  by  the  bulb  tubes  shown  in  the  figure.  After  the  end  of 
the  operation  the  water  in  each  one  of  the  bulb  tubes  is  washed 
back  into  its  proper  flask  with  freshly  boiled  water.  During  the 
vigorous  evolution  of  hydrogen  at  the  beginning  of  the  operation, 
some  kind  of  safety  arrangement  is  necessary  to  prevent  the 
particles  of  soda-lye  being  carried  over  by  the  bubbles  of  that  gas. 
The  siphon  bulb  shown  in  the  figure  is  found  effective  for  this 
purpose.  In  this  operation  better  results  are  obtained  by  condens- 
ing the  escaping  steam,  and  for  this  reason. the  block  tin  tubes  are 


INVESTIGATIONS    OF    BECK  437 

conducted  through  a  tank  supplied  with  a  current  of  cold  water. 
The  ends  of  the  tubes  should  not  dip  below  the  surface  of  the 
liquid  in  the  receivers.  When  the  condensed  liquid  collects  in 
considerable  quantities  in  the  safety  tube  the  lamp  should  be 
extinguished  under  the  flask,  which  permits  the  return  of  the 
liquid  to  the  flask  by  means  of  the  siphon.  This  should  be  done 
two  or  three  times  during  the  progress  of  the  distillation  to  pre- 
vent a  too  high  concentration  of  the  soda-lye,  thus  endangering  the 
flask.  The  excess  of  the  acid  in  the  receiver  is  determined  by 
titration,  as  in  the  regular  kjeldahl  method.  Blank  determina- 
tions are  made,  from  time  to  time,  and  corrections  made  in  har- 
mony therewith. 

377.  Investigations  of  Beck. — A  late  contribution  to  the 
analysis  of  Chile  saltpeter  is  that  of  Beck.59 

Beck  examined  the  direct  method  of  Ulsch,  subsequently  de- 
scribed, and  the  indirect  method  which  is  so  commonly  em- 
ployed by  dealers,  depending  on  the  determination  of  the  other 
principal  ingredients  and  subtracting  this  from  100  to  get  the  per 
cent,  of  nitrate  of  soda  in  the  mixture.  This  last  method  is  par- 
ticularly unsatisfactory,  since  it  gives  1.5  per  cent,  of  sodium  ni- 
trate too  much.  The  quantity  of  perchlorate  which  is  present  is 
also  important  and  for  technical  purposes,  such  as  the  nitration 
of  cellulose,  etc.,  it  is  recommended  not  to  use  any  sample  which 
yields  more  than  one  per  cent,  of  a  sodium  salt  due  to  perchlorate. 

Beck  expresses  the  hope  that  the  producers  of  Chile  saltpeter 
in  the  future  will  cease  to  urge  the  use  of  the  indirect  method 
and  will  refrain  from  attacking  the  validity  of  the  direct  methods, 
and  calls  attention  to  the  fact  that  the  increasing  possibility  of 
producing  nitric  acid  and  nitrates  directly  from  the  atmosphere 
may  supersede  the  necessity  of  using  the  natural  salt. 

The  factors  for  calculating  the  percentage  of  nitric  acid  when 
it  is  reduced  to  ammonia  may  be  based  upon  the  number  of  cubic 
centimeters  of  half-normal  suifuric  acid  required  for  10  cubic 
centimeters  of  a  solution  containing  33  grams  of  sodium  nitrate  in 
one  liter.  The  factors  are  as  follows: 

w  Zeitschrift  fur  analytische  Chemie,  1906,  45  :  669. 


AGRICULTURAL   ANALYSIS 


For  N  :  2.125  0°g  =  0.32783) 

"     N2O5'-         8.188  (log  =  0.91318) 
"     NaNO3:   12.893  Og  =  1.11318) 

378.  Method  of  Devarda.  —  The  inconvenience  due  to  slow 
action  and  other  causes,  arising  from  the  use  of  pure  metals  in  the 
reduction  of  nitrates  to  ammonia,  has  been  overcome,  to  some 
extent,  by  Devarda,  by  use  of  an  alloy,  in  a  state  of  fine  powder, 
consisting  of  aluminum,  copper,  and  zinc.60  The  alloy  consists  of 
45  per  cent,  of  aluminum,  50  per  cent,  of  copper,  and  five  per 
cent,  of  zinc.  In  dissolving,  the  copper  is  left  in  a  finely  divided 
state,  which  is  a  great  help  in  distillation  in  preventing  bumping. 

The  analytical  process  is  carried  out  as  follows  :  The  solution 
containing  the  nitrate,  in  quantity  equivalent  to  about  one-half 
gram  of  potassium  nitrate,  is  placed  in  a  flask  having  a  capacity 
of  about  one  liter,  and  diluted  with  60  cubic  centimeters  of  water 
and  five  cubic  centimeters  of  alcohol,  after  which  40  cubic  cen- 
timeters of  caustic  potash  solution,  of  specific  gravity  1.3  are 
added.  From  two  to  two  and  one-half  grams  of  the  alloy  de- 
scribed above  are  introduced,  and  the  flask  attached  to  a  conden- 
ser with  a  receiver  containing  standard  acid.  The  connection 
between  the  flask  and  the  condenser  is  made  by  means  of  a  tube 
having  on  the  limb  next  the  flask  a  bulb  filled  with  glass  beads 
to  prevent  the  contents  of  the  flask  splashing  over  into  the  receiver, 
and  on  the  other  limb  another  bulb  to  prevent  the  acid  in  the  re- 
ceiver finding  its  way  into  the  distillation  flask,  should  regurgi- 
tation  occur.  When  the  flask  has  been  thus  connected  with  the 
condenser  it  is  gently  heated  for  half  an  hour,  at  the  end  of  which 
time  the  evolution  of  hydrogen  will  have  slackened  or  ceased,  and 
the  distillation  is  then  begun,  at  first  cautiously,  until  the  zinc  of 
the  alloy  has  completely  dissolved,  and  then  more  vigorously,  the 
time  necessary  being  about  20  minutes  from  the  time  when  the 
contents  of  the  flask  begin  to  boil.  The  distillate  is  caught  in 
standard  acid  and  the  ammonia  determined  by  titration  of  the 
residual  acid  in  the  ordinary  way.  It  is  to  be  noted  that  the 
strength  of  the  alkali  used  is  of  importance,  as,  if  it  be  too  strong, 
the  action  on  the  alloy  is  unduly  vigorous  at  the  beginning  of  the 
80  Chemiker-Zeitung,  1892,  16  :  1952. 


VARIATION    OF    STOKI.ASA 


439 


operation,  and  if  too  weak,  the  contents  of  the  flask  have  to  be 
heated  overmuch,  the  result  in  both  cases  being  the  formation  of 
a  fine  spray  of  caustic  solution,  which  is  very  difficult  to  stop,  even 
with  complicated  washing  attachments  to  the  distilling  flask.  The 
test  analyses  on  pure  nitrates  are  satisfactory.  This  method  has 
been  used  with  satisfaction  in  the  laboratory  of  the  Bureau  of 
Chemistry,  but  does  not  appear  to  have  any  special  advantage 
over  the  process  of  Ulsch,  to  be  described  further  on. 

379.  Variation  of  Stoklasa. — Stoklasa  has  subjected  the 
method  of  Devarda  to  a  comparative  test  with  the  following 
methods  :61 


Fig-  33-    Stoklasa's  Nitric  Acid  Apparatus. 

1.  Wagner's  schloesing-grandeau  method. 

2.  Lunge's  nitrometer  method. 

3.  Stutzer's  method. 

The  reduction  takes  place  in  a  copper  erlenmeyer  A,  Fig.  33,  in 
which,  in  addition  to  the  solution  containing  the  nitrate,  are  placed 
200  cubic  centimeters  of  water,  40  cubic  centimeters  of  potassium 
hydroxid  solution  of  33°  B.,  five  cubic  centimeters  of  alcohol,  and 
finally  two  and  one-half  grams  of  the  finely  powdered  devarda 
alloy.  The  distillate  passes  through  a  tube  B  filled  with  glass 
pearls  and  into  the  condenser  D  through  the  bulbs  CC'. 
61  Zeitschrift  fur  angewandte  Chemie,  1893,  6  : 161. 


44°  AGRICULTURAL  ANALYSIS 

After  the  flask  is  connected  with  the  distilling  apparatus,  it  is 
gently  warmed  and  the  reduction  is  ended  in  about  20  minutes. 
The  ammonia  which  is  formed  is  distilled  into  E,  containing  the 
standard  acid  S,  requiring  about  20  minutes  more.  The  com- 
parative results  given,  show  that  the  devarda  method  is  equally 
accurate  as  any  of  the  other  methods  mentioned,  giving  prac- 
tically theoretical  results. 

In  so  far,  however,  as  speed  of  an  analysis  is  concerned,  the 
first  place  is  awarded  to  the  lunge  nitrometer  method,  with  which 
a  complete  analysis  can  be  made  in  from  30  to  40  minutes.  In 
the  second  rank,  so  far  as  speed  is  concerned,  the  devarda  method 
is  recommended.  All  the  methods  give  accurate  results. 

380.  Method  of  Sievert. — Two  grams  of  potassium  or  sodium 
nitrate  are  dissolved,  and  the  solution  made  up  to  1000  cubic  cen- 
timeters.62 Fifty  cubic  centimeters  of  the  solution  are  placed  in 
a  600  cubic  centimeter  flask  and  diluted  with  50  cubic  centimeters 
of  water,  and  from  1 8  to  20  grams  of  caustic  alkali  added.  After 
the  alkali  is  dissolved,  75  cubic  centimeters  of  96  per  cent,  alcohol 
are  added  and  a  few  pieces  of  bone-black  to  prevent  foaming. 
From  10  to  15  grams  of  zinc  or  iron  dust  are  added  to  the  flask 
which  is  closed  and  connected  with  a  U-tube  holding  about  200 
cubic  centimeters,  which  contains  about  10  cubic  centimeters  of 
normal  sulfuric  acid.  This  U-tube  is  kept  cool  by  being  immersed 
in  water.  The  whole  mixture  is  allowed  to  stand  for  three 
or  four  hours  and  the  alcohol  is  distilled  slowly,  the  ammo- 
nia formed  by  the  reduction  of  the  nitrates  being  carried  over  with 
it.  The  distillation  lasts  for  about  two  hours.  The  contents 
of  the  U-tube  are  carefully  rinsed  into  a  dish  and  the  excess  of 
sulfuric  acid  titrated  with  one-fourth  normal  soda-lye. 

For  soil  extracts  and  substances  containing  unknown  quan- 
tities of  nitric  acid,  a  preliminary  test  will  indicate  approxi- 
mately the  amount  thereof,  and  this  will  be  an  indication  for 
the  quantity  to  be  used  in  the  analysis. 

The  method  of  Stutzer  differs  from  the  foregoing  in  the  em- 
ployment of  aluminum  dust  instead  of  iron  or  zinc.63  The  reducing 

61  Liebig's  Annalen  der  Chemie,  1862,  125  :  293. 
65  Zeitschrift  fur  angewandte  Chemie,  1890,  3  :  695. 


VARIATION  OF  THE  SODIUM-AMALGAM  PROCESS 


441 


power  of  aluminum,  however,  varies  greatly  according  to  the 
method  in  which  the  metal  has  been  prepared.  Pure  aluminum 
prepared  by  the  electric  method,  reduces  the  nitric  acid  much 
less  vigorously  than  the  metal  prepared  by  the  older  methods  of 
fusion  with  sodium.  For  this  reason  the  method  of  Stutzer  is 
not  to  be  preferred  to  that  of  Sievert. 

REDUCTION  IN  AN  ACID  SOLUTION 

381.  Variation  of  the  Sodium- Amalgam  Process. — This  method 
is  described  by  Monnier  and  Auriol.64 

The  principle  of  the  operation  depends  on  the  reduction  of 


Fig.  34.   Apparatus  of  Monnier  and  Auriol. 

the  dissolved  nitrate  by  titrated  sodium  amalgam  in  presence  of 
an  acid,  and  the  estimation  of  the  quantity  of  nitric  acid  present 
from  the  deficit  in  the  volume  of  hydrogen.  The  apparatus  em- 
ployed is  conveniently  mounted  as  shown  in  Fig.  34.  The  brass 
vessel  A  is  movable  by  means  of  the  cord  on  the  pulley  B,  in  such 

64  Archives  des  Sciences  physiques  et  naturelles,  Gendve,   1894,   [3], 
31  :  352. 


442  AGRICULTURAL  ANALYSIS 

a  way  as  to  be  fixed  at  any  required  altitude.  It  is  filled  with 
water  and  connected  by  a  rubber  tube  to  the  cooling  tube  D. 
Within  the  cooling  tube  there  is  a  graduated  cylinder  open  at  its 
lower  end.  Its  upper  end  is  connected  directly  with  the  apparatus 
C.  The  cooling  tube  D  has  a  small  side  tube  c  near  its  upper 
end,  by  means  of  which  the  air  can  enter  or  escape  when  the 
position  of  A  is  changed.  The  apparatus  C,  in  which  the  reaction 
takes  place,  is  a  glass  cylinder.  Its  upper  end  is  continuous  with 
the  T-tube  provided  with  the  stop-cocks  a  and  b.  One  arm  of 
the  T  permits  connection  with  the  graduated  measuring  tube  by 
means  of  a  rubber  union.  The  lower  end  of  C  is  closed  with  a 
large  hollow  ground-glass  stopper,  carrying  a  small  receptacle 
within,  so  that  it  forms  two  separate  water-tight  compartments, 
open  at  the  top. 

The  sodium  amalgam  is  prepared  as  follows : 

In  a  clay  crucible  are  heated  400  grams  of  mercury,  and, 
little  by  little,  with  constant  stirring,  four  grams  of  dry  sodium 
are  added.  When  cold,  the  amalgam  is  placed  in  a  burette,  hav- 
ing a  ground-glass  stopper,  and  covered  with  petroleum.  The 
strength  of  the  amalgam  is  established  in  the  following  manner. 
A  small  glass  thimble,  ground  even  at  the  top,  is  filled  with  the 
amalgam  and  struck  off  even  with  a  ground-glass  straight  edge. 
In  this  way  the  same  quantity  of  amalgam  is  taken  for  each  test. 
This  measured  portion  of  the  amalgam  is  placed  in  the  inner  ves- 
sel of  the  glass  stopper  to  C.  Ten  cubic  centimeters  of  water,  con- 
taining 60  centigrams  of  tartaric  acid,  are  placed  on  the  outer  ring 
of  the  glass  stopper,  which  is  then  inserted,  well  oiled,  in  C,  clos- 
ing it  air-  and  water-tight.  The  tartaric  acid  solution  also  carries 
a  piece  of  litmus  paper,  so  that  its  constant  acidity  may  be  in- 
sured. The  vessel  A  is  fixed  in  a  position  which  brings  the  water 
in  the  graduated  burette  and  tube  D  exactly  to  the  o  mark.  The 
cock  a  is  closed,  b  opened,  and  C  is  inverted  until  all  the  amalgam 
is  poured  into  the  solution  of  tartaric  acid.  The  evolved  hydro- 
gen mixed  with  the  air  contained  in  the  apparatus,  is  passed  into 
the  graduated  burette.  After  15  minutes,  the  reaction  is  ended. 
The  water  level  within  and  without  the  graduated  tube  is  restored 


METHOD   OF    SCHMITT  443 

and  the  volume  of  gas  evolved  noted  and  reduced  by  the  usual 
tables  to  o°  and  760  millimeters  pressure  of  the  barometer. 

An  amalgam  prepared  as  above  gives  about  three  cubic  centi- 
meters of  hydrogen  for  each  gram.  The  thimble  holds  from  12 
to  15  grams. 

The  estimation  of  nitric  acid  is  made  in  a  solution  containing 
about  one-tenth  per  cent,  of  nitrate.  Ten  cubic  centimeters  are 
used,  to  which  six-tenths  gram  of  tartaric  acid  is  added,  and  placed 
in  the  outer  part  of  the  glass  stopper.  The  rest  of  the  process  is 
conducted  exactly  as  described  above.  The  deficit  in  hydrogen 
is  calculated  to  nitrogen  pentoxid. 

The  reduction  by  sodium  amalgam  is  not  so  convenient  a  form 
of  estimating  nitric  acid  as  many  of  the  other  forms  of  using 
nascent  hydrogen.  As  practiced  by  calculating  from  the  deficit 
of  hydrogen,  however,  it  has  some  advantages  by  reason  of  the 
fact  that  no  heating  is  required.  The  presence  of  organic  neu- 
tral bodies,  or  even  those  of  an  acid  nature,  like  humus,  does  not, 
therefore,  interfere  with  the  work.  Likewise,  mineral  bodies 
in  solution,  which  are  not  reduced  by  nascent  hydrogen,  do  not 
interfere  with  the  accuracy  of  the  reaction. 

382.  Method  of  Schmitt. — In  the  method  of  Schmitt  40  cubic 
centimeters  of  glacial  acetic  acid  are  placed  in  a  flask  of  600  cubic 
centimeters  content,  and  15  grams  of  a  mixture  of  zinc  and  iron 
dust  added.65  To  this  quantity  of  the  solution  containing  the 
nitrate,  representing  about  half  a  gram  of  the  pure  nitrate,  is  added 
with  constant  shaking,  in  portions  which  do  not  evolve  hydrogen 
too  rapidly.  After  about  15  minutes  when  the  evolution  of  hydro- 
gen has  somewhat  diminished,  an  additional  15  grams  of  the 
metal  dust  are  added.  If  the  contents  of  the  flask  become  thick 
they  are  diluted  with  water.  The  reduction  is  complete  in  from 
30  to  40  minutes.  The  contents  of  the  flask  are  saturated  with 
enough  soda-lye  not  only  to  neutralize  the  excess  of  acetic  acid, 
but  to  keep  the  zinc  hydroxid  also  in  solution.  For  this  purpose 
about  200  cubic  centimeters  of  soda-lye  of  1.25  specific  gravity  are 
necessary.  The  ammonia  is  obtained  by  distillation  into  standard 
acid  in  the  usual  way. 

65  Chemiker-Zeitung,  1890,  14  :  1410. 


444  AGRICULTURAL  ANALYSIS 

The  flask  is  covered  during  the  reduction  to  prevent  loss  by 
spraying.  It  must  be  noted  that  it  is  essential  that  the  iron  be 
finely  divided ;  it  is  mixed  with  the  powdered  zinc  in  equal  parts. 

The  total  nitrogen  can  be  determined  in  guanos  and  nitrate 
mixtures  by  the  following  simple  alteration  in  procedure:  One 
gram  of  the  substance  is  dissolved  in  water,  five  cubic  centimeters 
of  glacial  acetic  acid,  and  from  two  to  three  grams  of  the  mixed 
metallic  powder  added,  and  the  whole  gently  heated  for  10  or  15 
minutes.  After  the  contents  of  the  flask  have  cooled,  25  cubic 
centimeters  of  sulfuric  acid  are  cautiously  added  in  small  portions, 
undue  frothing  being  restrained  by  the  addition  of  a  fragment 
of  paraffin  wax.  The  acetic  acid  is  driven  off  by  heating,  and  the 
remaining  contents  of  the  flask  boiled  until  the  organic  matter  is 
completely  decomposed  as  in  the  kjeldahl  process.  About  two 
hours  boiling  is  required.  Neutralization  and  distillation  are  ac- 
complished as  in  the  ordinary  manner.  The  method  is  also  ap- 
plicable to  the  determination  of  nitrates  in  drinking  water,  provid- 
ed nitrites  and  ammonia  be  absent. 

383.  Method  of  Ulsch. — In  practice  the  method  of  Ulsch  has 
come  into  general  use.66 

For  the  determination  of  nitrogen  in  nitrates  by  this  method 
half  a  gram  of  saltpeter  or  four-tenths  gram  of  sodium  nitrate 
is  dissolved  in  25  cubic  centimeters  of  water,  in  a  flask  with  a 
content  of  about  600  cubic  centimeters.  Five  grams  of  iron  re- 
duced by  hydrogen,  and  10  cubic  centimeters  of  sulfuric  acid 
diluted  with  two  volumes  of  water  are  then  added  to  the  flask. 
To  avoid  mechanical  losses  during  the  evolution  of  hydrogen,  a 
pear-shaped  glass  stopper  is  hung  in  the  neck  of  the  flask.  After 
the  first  violent  evolution  of  hydrogen  has  passed,  the  flask  is 
slowly  heated  until,  in  about  four  minutes,  it  is  brought  to  a  gentle 
boil.  The  boiling  is  continued  for  about  six  minutes  when  the 
reduction  is  complete.  About  50  cubic  centimeters  of  water  are 
added,  an  excess  of  soda-lye  and  a  few  particles  of  zinc ;  then  the 
ammonia  is  distilled  and  collected  in  standard  acid  in  the  usual 
way. 

The  method  of  Ulsch  can  also  be  applied,  according  to  Fricke, 
86  Chemisches  Central-Blatt,  1890,  2  :  926. 


ULSCH     METHOD  445 

to  the  analysis  of  nitrates  contained  in  drinking  and  drainage 
waters,  and  it  is  regarded  by  him  as  one  of  the  best  methods  to 
be  employed  in  such  investigations.67 

The  method  of  Ulsch  has  given  entirely  satisfactory  results,  and 
is  generally  used  in  preference  to  other  methods  in  cases  where 
a  considerable  quantity  of  nitrates  is  present.  It  is  based  on  the 
following  reactions: 

2KNO,+H2SO4=K2SO4+2HNO, 

2HNO3+8H,=2NH34-6H2O 

2NH.+Has64=(NHJ1Sb4. 

384.  Ulsch  Method  Applicable  to  Mixed  Fertilizers. — The 
method  of  Ulsch,  which  is  found  to  give  good  results  with  pure 
nitrates  or  with  nitrates  in  the  absence  of  other  forms  of  nitrogen, 
may  also  be  adapted  to  mixed  fertilizers  containing  nitrogen  in 
more  than  one  form.  Street  has  developed  such  a  method  and 
shown,  by  analytical  data,  that  it  is  applicable  in  a  great  num- 
ber of  cases.08  The  variation  is  based  on  the  substitution  of  mag- 
nesia for  soda  in  the  distillation  and  is  carried  on  as  follows : 

Place  one  gram  of  the  sample  in  a  half-liter  flat-bottomed  flask. 
Add  about  30  cubic  centimeters  of  water,  one  gram  of  reduced 
iron,  and  10  cubic  centimeters  of  sulfuric  acid  diluted  with  an 
•equal  volume  of  water,  shake  well,  and  allow  to  stand  for  a 
short  time.  This  will  remove  the  danger  of  an  explosion  caused 
by  the  otherwise  violent  action  which  takes  place.  Close  the 
neck  of  the  flask  with  a  rubber  stopper  through  which  passes  a 
glass  dropping-bulb  filled  with  water.  The  flask  having  been 
stoppered,  place  it  on  a  slab  to  which  a  moderate  heat  is  applied. 
Allow  the  solution  to  come  slowly  to  a  boil  and  then  boil  for 
five  minutes  and  cool.  Add  about  100  cubic  centimeters  of  water, 
a  little  paraffin,  and  about  five  grams  of  magnesium  oxid.  Boil 
for  40  minutes,  after  which  time  all  the  ammonia  will  be  dis- 
tilled, and  collect  the  ammonia  in  set  acid. 

The  magnesia  causes  a  slight  frothing,  which  can  easily  be 
•controlled  by  adding  a  little  paraffin  and  by  bringing  to  a  boil 
very  gradually.  Fully  40  minutes  are  necessary  to  distil  all  the 

87  Zeitschrift  fiir  angewandte  Chemie,  1891,  4  :  241. 
68  Division  of  Chemistry,  Bulletin  35,  1892  :  88. 


446  AGRICULTURAL  ANALYSIS 

ammonia.  Tests  were  made  after  boiling  for  30  minutes  and 
traces  of  ammonia  were  still  found ;  after  40  minutes  these  traces 
entirely  disappeared. 

The  method  is  a  quick  one.  One  man  can  easily  do  six  deter- 
minations at  a  time,  and  these  six  determinations  can  be  made 
in  but  a  little  over  an  hour.  Magnesia  gives  results  closely  agree- 
ing with  theory  and  causes  a  very  slight  frothing,  which  can  be 
easily  controlled.  One  gram  of  reduced  iron  is  sufficient  in  all 
ordinary  complete  fertilizers. 

Magnesia  is  preferred  to  caustic  soda  in  the  distillation  be- 
cause it  produces  less  frothing  and  by  reason  of  the  danger  of 
some  of  the  soda-lye  being  carried  over  mechanically  and  thus 
tending  to  produce  an  error  of  a  plus  nature.  In  the  use  of  mag- 
nesia, assurance  must  be  had  that  it  is  strongly  in  excess.  Being 
less  active  in  its  effects,  a  longer  time  for  the  distillation  must 
be  taken  than  when  soda-lye  is  used.  The  modified  ulsch  method 
just  described  is  recommended  provisionally,  and  with  the  expec- 
tation that  each  analyst  will  ascertain  its  true  merits  before  allow- 
ing it  to  displace  longer  approved  processes. 

385.  Kruger's  Method  for  Nitric  Acid. — About  0.3  gram  of 
the  nitrate  dissolved  in  water  is  mixed  with  20  cubic  centimeters 
of  a  hydrochloric  acid  solution  of  stannous  chlorid  holding  150- 
grams  of  tin  per  liter.69  One  and  a  half  grams  of  spongy  tin 
prepared  by  the  action  of  zinc  on  stannous  chlorid  are  added. 
The  flask  containing  the  mixture  is  heated  until  the  tin  is  dis- 
solved, by  which  time  the  nitric  acid  is  completely  reduced.  The 
subsequent  distillation  and  titration  are  accomplished  as  usual. 
In  the  case  of  nitro  and  nitroso  compounds,  after  the  solution  of 
the  tin,  20  cubic  centimeters  of  sulfuric  acid  are  added  and 
heated  until  sulfuric  vapors  escape.  After  cooling,  the  amido 
substances  formed  are  oxidized  by  potassium  bichromate  before 
the  distillation  takes  place. 

Kriiger   also  estimates  the   nitrogen   in   benzol,   pyridin,   and 

chinolin  derivatives  by  dissolving  them  in  sulfuric  acid,  using 

from  0.2  to  0.8  of  a  gram  of  the  alkaloidal  bodies,  and,  after 

cooling  the  solution,  oxidizing  by  adding  finely  powdered  potas- 

<*  Berichte  der  deutschen  chemischen  Gesellschaft,  1894,  27  :  609,  1636. 


METHOD  OF  WILUAMS-WARINGTON  447 

sium  bichromate.  About  half  a  gram  more  of  the  potassium 
bichromate  should  be  used  than  is  necessary  for  the  oxidation  of 
the  substances  in  solution.  The  entire  oxidation  does  not  con- 
sume more  than  from  15  to  30  minutes. 

REDUCTION  OF  THE  ELECTRIC  CURRENT 

386.  Method  of  Williams -Warington. — This  process  is  appli- 
cable to  solutions  or  extracts  of  fertilizers,  soils,  etc.,  and  rain 
or  drainage  waters  containing  only  a  small  amount  of  nitrates. 
From  the  losses  which  naturally  occur  during  the  evaporation  of 
water,  even  with  all  the  precautions  usually  observed,  Waring- 
ton was  led  to  try  some  method  for  the  determination  of  nitrates 
and  nitrites  in  waters  without  previous  concentration.70  The  re- 
duction of  these  bodies  by  the  copper-zinc  couple  formed  the 
basis  of  these  experiments,  and  they  resulted  in  the  following 
method  of  manipulation,  which  is  based  on  a  process  devised  by 
\Villiams.71 

The  method  consists  in  boiling  rapidly  one  liter  of  the  solution 
•of  a  fertilizer  or  rain  water  in  a  retort,  with  a  little  magnesia 
previously  raised  to  a  low  red  heat  and  then  washed,  until  250 
cubic  centimeters  have  distilled.  The  residue  is  made  up  to  800 
•cubic  centimeters,  transferred  to  a  wide-mouthed,  stoppered  bot- 
tle supplied  with  strips  of  copper  and  zinc  forming  electric 
•couples,  and  set  aside,  at  a  temperature  of  from  21°  to  24°,  for 
three  days.  A  measured  portion  of  the  solution  is  distilled  and 
the  ammonia  determined  in  the  distillate  by  nesslerizing. 

This  plan  has  two  advantages :  First,  the  ammonia,  as  well  as 
the  nitrogen  as  nitrates  and  nitrites,  can  be  determined  in  the 
•course  of  the  same  operation  and  in  the  same  sample  of  the  solu- 
tion. For  this  purpose  it  is  only  necessary  to  fit  the  retort  to  an 
efficient  condenser  to  remove  all  ammonia  from  the  apparatus  by 
boiling  distilled  water  in  the  retort  before  introducing  the  solu- 
tion. The  distillate  of  250  cubic  centimeters  obtained  as  De- 
scribed above,  is  well  mixed  and  the  ammonia  determined  in 
from  25  to  100  cubic  centimeters  thereof,  diluted  to  150  cubic 
•centimeters  with  ammonia-free  water.  The  nitrogen,  as  nitrates 

70  Journal  of  the  Chemical  Society,  1889,  55  :  538. 

71  Journal  of  the  Chemical  Society,  1881,  39  :  100. 


448  AGRICULTURAL  ANALYSIS 

and  nitrites,  is  determined  directly  and  alone.  The  error  of  the 
determination  is  as  small  as  nesslerizing  admits  of,  since  it  is 
possible,  if  necessary,  to  distil  until  the  full  amount  of  ammonia 
is  obtained. 

The  determination  of  nitric  nitrogen,  in  a  given  sample,  by 
the  above  method  gave  a  mean  quantity  of  product  of  0.162  part 
per  million,  while  the  determination,  in  the  same  sample,  by  the 
modified  schloesing  method,  gave  0.125  part  per  million.  This 
result  confirms  the  supposition  that  in  the  complete  evaporation 
necessary  to  the  manipulation  of  the  schloesing  method  there  is 
a  loss  of  nitrogen. 

387.  Nitrogen  in  Rain  Water. — The   amount  of  nitrogen  as 
nitrates  and  nitrites  in  the  rain  water  at  Rothamstead,  for  the 
12  months  ending  April  i,  1888,  was  found,  by  the  schloesing 
method,  to  be  0.614  pound  per  acre,  the  total  rainfall  being  21.96 
inches.     For  the  year  ending  April  i,  1889,  by  the  copper-zinc 
method,  it  amounted  to  0.917  pound  per  acre,  the  total  rainfall 
being  29.27  inches.     The  amounts  found  in  other  localities  are 
quite  different  from  the  above,  as,   for  instance,  the  mean  of 
seven  stations  in  Germany  for  13  years,  beginning  in  1864,  shows 
10.18  pounds  of  nitrogen  per  acre.    The  average  amount  for  10- 
years   at  the  observatory  of   Mont   Sauris,   near   Paris,   shows 
12.36  pounds  of  nitrogen  per  acre.     The  average  for  three  years 
at  Lincoln,  as  determined  by  Professor  G.  Gray,  shows  1.6  pounds 
of  nitrogen  per  acre  per  annum.     At  Tokio,  in  Japan,  Kellner 
found,  for  one  year,  1.02  pounds  per  acre. 

388.  Determination   of  the   Ammonia. — The   method   used   at 
Rothamstead  is  to  make  one  determination  of  ammonia  in  the 
whole  of  the  distillate  obtained,  the  strength  of  which  is  regu- 
lated by  varying  the  amount  introduced  into  the  retort,  so  that 
it  shall  be  equal  to  about  two  cubic  centimeters  of  the  standard 
ammonia  solution.    A  150  cubic  centimeter  cylinder  is  first  filled 
with  the  rain  water,  and  50  cubic  centimeters  of  nessler  reagent 
added.     The  depth  of  tint  indicates  what  quantity  of  rain  water 
will  be  required  for  distillation.     This  having  been  determined, 
the  appropriate  volume  of  the  rain  water,  provided  it  does  not 
exceed  600  cubic  centimeters,  is  placed  in  the  retort  described' 


ALUMINUM-MERCURY    COUPLE    FOR    COPPER-ZINC  449 

above,  and  the  distillation  continued  until  the   150  cubic  centi- 
meter cylinder  is  filled.    The  titration  is  made  in  the  usual  way. 

389.  Preparation  of  the  Copper-Zinc  Couple. — For  800  cubic 
centimeters  of  boiled  rain  water,  prepared  as  described,  six  strips 
of  zinc  foil,  four  inches  long  by  one  and  a  quarter  inches  wide, 
are  bent  at  right  angles  along  their  center  to  obtain  stiffness. 
The  zinc  strip  is  cleansed  and  coated  with  copper  by  washing  in 
a  series  of  five  beakers  containing,  respectively,  dilute  solution 
of  sodium  hydroxid,  very  dilute  sulfuric  acid,  a  three  per  cent, 
solution  of  copper  sulfate,  ordinary  distilled  water,  and  distilled 
water  free  from  ammonia.     Through  these  five  beakers  the  zinc 
foil  is  successively  passed.     It  is  rinsed  both  after  the  alkali  and 
the  acid,  but  after  the  copper  has  been  deposited,  the  strips  are 
simply   drained  and  carefully   placed  in  the   distilled   water,   it 
being  difficult  to  rinse  without  removing  the  copper.    The  couples 
should  be  entirely  submerged  when  placed  in  the  rain  water.    The 
strips  should  remain  in  the  copper  sulfate  solution  long  enough 
to  be  well  covered  with  copper. 

390.  Substitution  of  an  Aluminum-Mercury  Couple  for  Copper- 
Zinc. — Ormandy  and  Cohen  have  proposed    to    use    an    alumi- 
num-mercury couple  for  the  copper-zinc  in  the  process  described 
above.72 

This  couple  acts  more  quickly  than  the  copper-zinc,  and  the 
results  are  equally  accurate.  Nitrites  are  reduced  in  about  one 
hour  by  this  apparatus,  while  the  zinc-copper  couple  of  Glad- 
stone and  Tribe  requires  about  six  times  as  long.  Aluminum  foil, 
free  of  grease,  should  be  used.  The  foil  should  be  heated  over 
a  bunsen  just  before  amalgamation.  The  clean,  very  thin  foil  is 
coated  with  mercury  by  shaking  with  a  concentrated  solution  of 
mercuric  chlorid.  It  should  be  prepared  immediately  before  use. 

The  amalgamated  foil  is  introduced  into  the  sample  of  solution 
to  be  analyzed,  and  left  until  all  the  aluminum  is  converted  into 
oxid.  The  presence  of  the  oxid  favors  the  prevention  of  bump- 
ing during  the  subsequent  distillation.  The  distilled  ammonia, 
collected  in  dilute  acid,  is  determined  by  nesslerizing,  the  free 

72  Journal  of  the  Chemical  Society,  1890,  57  :  811. 
15 


45°  AGRICULTURAL  ANALYSIS 

ammonia  in  the  sample  having  been  previously  determined.  The 
increase  in  ammonia  is  due  to  nitrates  or  nitrites  reduced  by  the 
couple. 

IODOMETRIC  ESTIMATION  OF  NITRIC  ACID  IN 
NITRATES 

391.  Method  of  De  Eoninck  and  Nihoul. — This  process  is 
applicable  only  in  the  absence  of  organic  bodies  and  other  reduc- 
ing agents. 

The  principle  on  which  it  rests,  as  applied  by  McGowan,  is 
as  follows73 

When  a  fairly  concentrated  solution  of  a  nitrate  is  warmed 
with  an  excess  of  pure,  strong  hydrochloric  acid,  the  nitrate  is 
completely  decomposed,  and  the  production  of  nitrosyl  chlorid 
and  chlorin  is  quantitative.  The  reaction,  as  shown  by  Tilden, 
is  represented  by  the  following  equation  :74 

HNO3+3HCl=NOCl-fCl2+2H2O. 

One  molecule  of  nitric  acid  thus  yields  two  atoms  of  chlorin 
and  one  molecule  of  nitrosyl  chlorid  capable  of  setting  free  three 
atoms  of  iodin.  The  iodin  can  be  estimated  in  the  usual  man- 
ner by  titration  with  sodium  thiosulfate.  The  nitrosyl  chlorid  is 
decomposed  by  the  potassium  iodid,  nitric  oxid  escaping. 

The  apparatus  employed  is  shown  in  Fig.  35. 

A  is  a  small,  round-bottomed  flask,  into  the  neck  of  which  a 
glass  stopper  x  is  accurately  ground.  The  capacity  of  the  bulb 
is  about  46  cubic  centimeters^  and  the  length  of  the  neck,  from  x 
to  y,  90  millimeters.  The  first  condenser  is  a  simple  tube,  slightly 
enlarged  at  the  foot  into  two  small  bulbs.75  The  length  from  a 
to  b  is  300  millimeters,  from  b  to  c  180  millimeters,  and  from  e 
to  /  30  millimeters.  The  capacity  of  the  bulb  B  is  25  cubic  centi- 
meters, and  the  total  capacity  of  the  two  bulbs  and  tube,  up  to 
the  top -of  C,  41  cubic  centimeters.  This  condenser  is  immersed 
up  to  the  level  of  c,  in  a  beaker  of  water.  D  is  a  geissler  bulb 
apparatus,  E  is  a  calcium  tube,  filled  with  broken  glass,  which  acts 
as  a  tower  and  g  is  a  small  funnel,  attached  by  rubber  and  clip 

n  Journal  of  the  Chemical   Society,  1891,  59  :  530. 

74  Journal  of  the  Chemical  Society,  1874,  27  :  630;  1875,  28  :  514. 

76  Sutton,  Volumetric  Analysis,  gth  Edition,  1907  :  77. 


METHOD  OF  DE  KONINCK  AND  NIHOUL 


451 


to  the  branch  T-tube  h.  Between  the  T-tube  *  and  the  wash- 
bottle  for  the  carbon  dioxid  is  placed  a  short  piece  of  glass  tub- 
ing, s,  containing  a  strip  of  filter  paper,  slightly  moistened  with 
iodid  of  starch  solution.  This  tube  j  is  really  hardly  necessary, 
as  no  chlorin  escapes  backwards  if  a  moderate  current  of  carbon 
dioxid  is  kept  passing,  but  it  serves  as  a  check.  A  glance  at  the 
joints  o,  p,  and  q,  which  are  of  narrow  india-rubber  tubing,  is 
sufficient  to  show  that,  by  using  this  arrangement,  practically  no 
rubber  is  exposed  to  the  action  of  the  chlorin.  The  tiny  piece 


Figure  35. 


McGowan's  Apparatus  for  the  lodometric 
Estimation  of  Nitric  Acid. 


of  rubber  tubing  at  the  joint  o  may  be  done  away  with,  the  nar- 
rower tube  there  being  accurately  ground  into  the  wider  one  ;  this 
makes  the  condensing  apparatus  practically  perfect. 

The  actual  operation  is  performed  in  the  following  manner: 
The  evolution  flask  is  washed  and  thoroughly  dried,  and  the 
nitrate  (say,  about  0.25  gram  of  potassium  nitrate)  is  introduced 
from  the  weighing  tube.  Two  cubic  centimeters  of  water  are 
added,  and  the  bulb  is  gently  warmed,  so  as  to  bring  the  nitrate 
into  solution,  after  which  the  stopper  of  the  flask  is  firmly  inserted. 
About  15  cubic  centimeters  of  a  solution  of  potassium  iodid  (one 
in  four)  are  run  into  the  first  condensing  tube,  any  iodid  adher- 
ing to  the  upper  portion  of  the  tube  being  washed  down  with  a 
little  water,  and  five  cubic  centimeters  of  the  same  solution,  mixed 


452  AGRICULTURAL  ANALYSIS 

with  from  eight  to  10  cubic  centimeters  of  water,  are  sucked  in- 
to the  geissler  bulbs  while  the  glass  in  the  tower  E  is  also  thor- 
oughly moistened  with  the  iodid.  The  geissler  bulbs  should  be  so 
arranged  that  gas  bubbles  through  only  the  'last  of  them,  the 
liquid  in  the  others  remaining  quiescent. 

All  the  joints  having  been  made  tight  the  carbon  dioxid  is 
turned  on  briskly  and  passed  through  the  apparatus  until  a 
small  tubeful  collected  at  /,  over  caustic  potash  solution,  shows 
that  no  appreciable  amount  of  air  is  left  in  it.  The  small  outlet 
tube  /  is  replaced  by  a  tube,  filled  with  broken  glass  which  has 
been  moistened  with  the  above-mentioned  iodid  solution,  and 
closed  by  a  cork  through  which  an  outlet  tube  passes,  the  object 
of  this  trap  tube  being  to  prevent  any  air  getting  back  into  the 
apparatus.  The  brisk  current  of  carbon  dioxid  is  continued  for  a 
minute  or  two  longer,  so  as  to  practically  expel  vall  the  air  from 
this  last  tube.  The  stream  of  gas  is  now  stopped  for  an  instant, 
and  about  15  cubic  centimeters  of  pure  concentrated  hydrochloric 
acid,  free  from  chlorin,  run  into  A  through  the  funnel  g  (into 
the  tube  of  which  it  is  well  to  have  run  a  few  drops  of  water 
before  beginning  to  expel  the  air  from  the  apparatus),  and  A  is 
shaken  so  as  to  mix  its  contents  thoroughly.  A  slow  current  of 
carbon  dioxid  is  again  turned  on  (one  to  two  bubbles  through  the 
wash-bottle  per  second),  and  A  is  gently  warmed  over  a  burner. 
It  is  a  distinct  advantage  that  the  reaction  does  not  begin  until 
the  mixed  solutions  are  warmed,  when  the  liquid  becomes  orange- 
colored,  the  color  again  disappearing  after  the  nitrosyl  chlorid 
and  chlorin  have  been  expelled.  The  warming  is  very  gentle 
at  first  in  order  to  make  sure  of  the  conversion  of  all  the  nitric 
acid,  and  also  because  the  first  escaping  vapors  are  relatively  very 
rich  in  chlorin;  afterwards  the  liquid  in  A  is  briskly  boiled.  A 
very  little  practice  enables  the  operator  to  judge  as  to  the  proper 
rate  of  warming.  When  the  volume  of  liquid  in  A  has  been  re- 
duced to  about  seven  cubic  centimeters  (by  which  time  it  is  again 
colorless),  the  stream  of  carbon  dioxid  is  slightly  quickened  and 
the  apparatus  allowed  to  cool  a  little.  The  burner  is  now  set 
aside  for  a  few  minutes,  and  two  cubic  centimeters  more  of  hydro- 
chloric acid,  previously  warmed  in  a  test-tube,  run  in  gently 


METHOD  OF  GOOCH  AND  GRUENER  453 

through  g;  there  is  no  fear  either  of  the  iodid  solution  running 
back,  or  of  any  bubbles  of  air  escaping  through  y  if  this  is  done 
carefully.  This  is  a  precautionary  measure,  in  case  a  trace  of 
the  liberated  chlorin  might  have  lodged  in  the  comparatively  cool 
liquid  in  the  tube  h.  The  carbon  dioxid  is  once  more  turned 
on  slowly  and  the  liquid  in  A  is  boiled  again  until  it  is  reduced 
to  about  five  cubic  centimeters.  It  is  now  only  necessary  to  al- 
low the  apparatus  to  cool,  passing  carbon  dioxid  all  the  time, 
after  which  the  contents  of  the  condensers  are  transferred  to 
a  flask  and  titrated  with  thiosulfate.  At  the  end  of  a  properly 
conducted  experiment,  the  glass  in  the  upper  part  of  tower  E 
should  be  quite  colorless  and  there  should  be  only  a  mere  trace 
of  iodin  showing  in  the  lower  part  of  the  tower,  while  the  liquid 
in  the  last  bulb  of  the  geissler  apparatus  ought  to  be  pale  yellow. 
During  the  operation,  the  stopper  of  A  and  the  various  joints 
can  be  tested  from  time  to  time  by  means  of  a  piece  of  iodid  of 
starch  paper,  and  before  disjointing  it  is  well  to  test  the  escaping 
gas  (say  at  m)  in  the  same  way,  to  make  sure  that  all  nitric  oxid 
has  been  thoroughly  expelled. 

The  method  is  capable  of  giving  accurate  results,  but  it  is 
not  preferable  to  the  reduction  or  colorimetric  processes. 

392.  Method  of  Gooch  and  Gruener. — The  principle  on  which 
this  method  rests  depends  on  the  decomposition  of  a  nitrate  in 
presence  of  a  hot  saturated  solution  of  manganous  chlorid  and 
hydrochloric  acid  in  an  atmosphere  of  carbon  dioxid.76  The 
products  of  decomposition  are  passed  into  a  solution  of  potas- 
sium iodid  and  the  liberated  iodin  is  titrated  with  standard  sodium 
thiosulfate.  The  products  of  the  reaction  are  chlorin,  nitric 
oxid,  and  possibly  nitrosyl  chlorid,  and  under  proper  precautions 
the  iodin  set  free  is  quantitatively  proportional  to  the  weight 
of  nitrate  decomposed.  The  manganous  mixture  is  acted  on 
slowly  at  ordinary  temperatures,  but  on  heating,  the  nitrate  is 
decomposed  with  the  formation  of  a  higher  manganese  chlorid  and 
nitric  oxid.  When  the  heat  is  continued  a  sufficient  length  of 
time  the  chlorin  from  the  higher  chlorids  is  evolved  and  only 
manganous  chlorid  remains.  During  the  heating  the  color  of 

n  American  Journal  of  Science,  1892,  [3],  44  :  117. 


454 


AGRICULTURAL  ANALYSIS 


the  solution  passes  from  green  to  black  and  at  the  end  the  green 
color  is  restored.  The  apparatus  employed  is  shown  in  Fig.  36. 
A  plain  pipette  bent  as  is  shown  in  the  figure  serves  as  the 
generating  flask  and  for  the  attachment  on  the  one  hand  to  the 
carbon  dioxid  apparatus  and  on  the  other  to  the  system  of  ab- 
sorption bulbs  for  holding  the  potassium  iodid.  The  latter 
should  be  glass,  sealed  to  the  evolution  bulb  of  the  pipette  to  pre- 
vent the  action  of  the  evolved  gases  on  organic  materials.  The 
point  of  the  potassium  iodid  apparatus  is  drawn  out  so  as  to  be 
pushed  well  into  the  second  receiver,  being  held  in  place  by  a 


Figure  36.    Apparatus  of  Gooch  and  Gruener. 

piece  of  rubber  tubing.  The  third  receiver  acts  simply  as  a  trap  to 
exclude  the  air  from  the  absorption  apparatus.  The  first  receiver 
contains  in  solution  three  grams,  the  second  one,  and  the  third  a 
fraction  of  a  gram  of  potassium  iodid  for  each  one  tenth  of  a 
gram  of  nitrate  used.  During  the  reaction  the  first  re- 
ceiver is  kept  cool  by  immersion  in  water.  Before  connecting 
the  apparatus  with  the  carbon  dioxid  generator  the  solution  of 
manganous  chlorid  and  afterwards  the  nitrate  solution  are  drawn 
into  the  bulb  of  the  pipette  by  gentle  suction.  After  connecting 
the  apparatus  the  current  of  carbon  dioxid  is  started  and  kept 
up  until  all  the  air  is  expelled.  Heat  is  then  applied  to  the 
bulb  of  the  pipette  and  the  distillation  continued  until  all  the 
liquid  has  passed  over.  At  the  end  of  the  reaction  the  contents 


DELICACY  OF   THE   METHOD  455 

of  the  receivers  are  united  by  disconnecting  the  apparatus  from 
the  carbon  dioxid  generator  and  passing  water  through  the 
pipette.  The  introduction  of  the  manganous  chlorid  into  the 
mixture  does  not  interfere  with  the  titration  of  the  iodin.  This 
is  accomplished  in  the  usual  way  with  sodium  thiosulfate  using 
starch  as  an  indicator.  The  quantity  of  material  used  contains 
about  the  amount  of  nitric  acid  that  is  found  in  two-tenths  of  a 
gram  of  potassium  nitrate.  This  method,  so  similar  to  the  pre- 
ceding, is  somewhat  less  complex,  and,  to  that  extent,  preferable 
to  it. 

ESTIMATION  OF  NITRIC  ACID  BY  COLORIMETRIC 
COMPARISON 

393.  Delicacy  of  the  Method. — The  remarkable  delicacy  of  those 
methods  of  chemical  analysis  which  depend  on  the  production 
of  a  pronounced  color,  which  can  be  compared  with  that  produced 
by  a  known  quantity  of  a  given  substance,  has  been  long  illus- 
trated by  the  nesslerizing  process  for  the  estimation  of  ammo- 
nia. By  such  methods  minute  amounts  of  substances  can  be 
quantitatively  determined  with  great  accuracy,  when  they  would 
escape  all  effort  for  their  estimation  by  gravimetric  methods. 
Processes  based  on  this  principle  are,  therefore,  peculiarly  appli- 
cable to  the  detection  and  estimation  of  oxidized  nitrogen  in 
waters,  fertilizer  and  soil  extracts,  whether  they  be  present  as 
nitric,  nitrous,  or  ammoniacal  compounds.  The  very  delicacy  of 
the  process  is  the  chief  objection  to  its  use  since,  except  in  the 
most  experienced  hands,  and  without  the  observance  of  all  of  the 
conditions  of  manipulation,  errors  may  vitiate  the  results. 

In  the  following  paragraphs  will  be  given  with  sufficient  detail 
for  the  needs  of  the  analyst,  the  principles  and  practice  of  the 
colorimetric  comparison  methods  which  have  been  approved  as 
best  by  the  experience  of  analysts.  These  methods  are  appli- 
cable especially  to  cases  in  which  only  minute  quantities  of  the 
substances  looked  for  are  present,  and  where  celerity  of  deter- 
mination is  especially  desirable.  They  are,  therefore,  of  espe- 
cial value  in  the  analysis  of  rain,  drainage,  and  irrigation  waters, 
and  of  soil  and  fertilizer  extracts  poor  in  oxidized  nitrogen. 


456  AGRICULTURAL  ANALYSIS 

394.  Hooker's  Method.  —  The  quantitative  action  in  this  method 
depends  upon  the  deep  green  coloration  given  by  nitric  acid,  when 
dissolved  in  sulfuric  acid  and  carbazol.77  Other  oxidizing  bodies, 
such  as  iron,  chlorin,  bromin,  chromic  acid,  etc.,  give  the  same 
reaction,  but  not  in  such  a  prominent  manner.  Such  bodies,  with 
the  exception  of  chlorin  and  iron,  are  not  often  found  in  the 
solutions  with  which  the  agricultural  chemist  is  occupied.  In 
the  application  of  the  process,  iron,  if  present,  in  quantities  greater 
than  one-tenth  part  per  one  hundred  thousand,  must  be  removed. 
Chlorids,  also,  even  when  present  in  very  small  quantities,  inter- 
fere with  the  delicacy  of  the  reaction  and  must  be  removed.  Eas- 
ily destructible  organic  matter  tends  to  lower  the  result,  but  not 
materially,  unless  present  in  large  excess.  Calcium  carbonate  and 
sulfate,  soda,  and  other  alkalies,  in  the  quantities  in  which  they  are 
usually  present  in  such  solutions,  do  not  affect  the  result. 

The  following  reagents  are  required: 

1.  Concentrated  sulfuric  acid. 

2.  An     acetic     acid     solution     of     carbazol  ;     diphenylimid, 


3.  A  sulfuric  acid  solution  of  carbazol. 

4.  Standard  solutions  of  potassium  nitrate. 

5.  A  solution  of  aluminum  sulfate. 

6.  A  solution  of  silver  sulfate. 

1.  The   sulfuric  acid   used   for   all   purposes   in   the   process 
should  be  entirely  free  from  nitrogen  oxids.     It  may  be  read- 
ily tested  by  dissolving  in  it  a  small  quantity  of  carbazol.     If  the 
solution  be  at  first  golden-yellow   or  brown,   the  acid  is  suffi- 
ciently pure;  if  it  be  green  or  greenish,  another  and  better  sam- 
ple must  be  found.     It  is  essential  also  that  the  specific  gravity 
of  the  acid  be  fully  1.84,  and  it  is  well  to  ascertain  that  this  is 
really  the  case. 

2.  The  acetic  acid  solution  is  prepared  by  dissolving  six-tenths 
gram  of  carbazol    in  about  90  cubic  centimeters   of   strongest 
acetic  acid,  by  the  aid  of  gentle  heat.     It  is  allowed  to  cool,  and 
is  then  made  up  to  100  cubic  centimeters  by  the  further  addition 

71  American  Chemical  Jourual,  1889,  11  :  249. 


HOOKER'S  METHOD  457 

of  acetic  acid.  The  exact  strength  of  this  solution,  is  of  no 
material  importance  to  the  success  of  the  process,  and  the  above 
proportions  have  been  selected  principally  because  they  are  con- 
venient. The  solution  will  remain  unchanged  for  several  months. 
The  use  of  this  solution  merely  facilitates  the  prepara- 
tion of  that  next  described,  which  will  not  keep,  and  has,  conse- 
quently, to  be  freshly  prepared  for  each  series  of  determinations. 

3.  The  sulfuric  acid  solution  of  carbazol  is  easily  made  in  a 
few  seconds,  but  it  is  advisable  to  allow  it  to  stand  from  one  and 
one-half  to  two  hours  before  using.     It  is  prepared  by  rapidly 
adding  15  cubic  centimeters  of  sulfuric  acid  to  one  cubic  centi- 
meter of  the  above  described  acetic  acid  solution.     This  quan- 
tity usually  suffices  for  from  two  to  three  nitrate  estimations. 
When  freshly  prepared  it  is  golden-yellow  or  brown;  it  changes 
gradually,  however,  and  in  the  course  of  one  and  one-half  or 
two  hours  it  becomes  olive-green.     This  change  is  probably  due 
to  traces  of  oxidizing  agents,  which  occur  in  the  sulfuric  and 
acetic  acids,  and  which,  although  not  present  in  sufficient  quan- 
tity to  act  immediately,  gradually  bring  about  the  reaction  de- 
scribed.    The  greenish  color  does  not  interfere  with  the  process, 
as  might  at  first  be  supposed ;  on  the  contrary,  the  solution  is  not 
sensitive  to  small  quantities  of  nitric  acid  until  it  has  undergone 
the  change  to  olive-green,  and  it  is  for  this  reason  that  it  should 
be  prepared  about  two  hours  before  required  for  use.    This  solu- 
tion may  be  thoroughly  depended  on  for  six  hours  after  prepara- 
tion.   The  intensities  of  color  produced  by  the  more  concentrated 
solutions  of  nitrates  after  this  time  gradually  approach  each  other 
and  become  ultimately  the  same. 

4.  The  standard  solutions  of  potassium  nitrate  are  very  readily 
prepared.    The  solutions  which  are  to  be  compared  directly  with 
the  waters  examined,  may  be  prepared  as  required,  but  if  many 
determinations  are  to  be  made  with  a  variety  of  samples,  it  will 
be  found  best  to  prepare  a  complete  series,  differing  from  each 
other  by  0.02  part  nitrogen  in  100,000.    This  series  may  include 
solutions  containing  quantities  of  nitrogen  in  100,000  parts,  rep- 
resented by  all  the  odd  numbers  from  0.03  up  to  0.39.     It  will 
be  found  convenient  to  prepare  them  in  quantities  of  100  cubic 


458  AGRICULTURAL  ANALYSIS 

centimeters  at  a  time,  from  a  stock  solution  of  potassium  nitrate 
which  contains  o.ooooi  gram  nitrogen,  or  0.000045  nitric  acid  in 
one  cubic  centimeter.  Each  cubic  centimeter  of  this  solution, 
when  diluted  to  100  cubic  centimeters,  represents  o.oi  nitrogen  in 
100,000,  and  consequently  if  it  is  desired  to  make  a  solution  con- 
taining 0.35  part  nitrogen  in  100,000,  35  cubic  centimeters  are 
made  up  to  100  cubic  centimeters,  and  so  on.  The  solution  of 
potassium  nitrate  (b)  is  best  prepared  from  a  stronger  one  (a) 
containing  o.oooi  gram  nitrogen  to  the  cubic  centimeter,  or 
0.7214  gram  potassium  nitrate  to  the  liter;  100  cubic  centimeters 
of  (a)  made  up  to  one  liter  give  the  solution  (b).  It  is  obvious 
that  the  series  of  solutions  above  described  could  be  made  directly 
from  (a),  but  by  first  making  (b)  greater  accuracy  is  secured. 

5.  For  purposes  which  will  be  presently  described,  a  solution 
of  aluminum  sulfate  is  required,  containing  five  grams  to  the 
liter.    The  salt  used  must  be  free  from  chlorin  and  iron ;  and  the 
solution  should  give  no  reaction  when  tested  with  carbazol. 

6.  The  solution  of  silver  sulfate  is  required  for  the  removal 
of  chlorin  from  the  water  or  soil  extract  to  be  examined.    It  is 
prepared  by  dissolving  4.3943  grams  of  the  salt  in  pure  distilled 
water  and  making  up  to  one  liter.     The  sulfate  is  preferably 
obtained  by  dissolving  metallic  silver  in  pure  sulfuric  acid.    The 
solution  should  be  tested  with  carbazol  in  the  same  way  as  will  be 
presently  described  for  water;  if  perfectly  pure,  no  reaction  will 
be  obtained.     As  silver  sulfate  is  often  prepared  by  precipitation 
from  the  nitrate,  it  is  very  apt  to  contain  nitric  acid,  and  conse- 
quently, if  the  source  of  the  salt  be  unknown,  this  test  should 
on  no  account  be  omitted.     The   analytical  process  is  carried 
on  as  follows: 

Two  cubic  centimeters  of  the  solution  containing  the  minute 
quantity  of  nitric  acid  are  carefully  delivered  by  means  of  a 
pipette  into  the  bottom  of  a  test-tube ;  four  cubic  centimeters  of 
sulfuric  acid  are  added,  and  the  solution  thoroughly  mixed  by 
the  help  of  a  glass  rod.  The  test-tube  is  then  immersed  in  cold 
water,  and  when  well  cooled  one  cubic  centimeter  of  the  sulfuric 
acid  solution  of  carbazol  is  added,  and  the  whole  again  mixed 
as  before.  The  intensity  of  the  color  is  observed,  and  a  little 


HOOKER'S  METHOD  459 

experience  enables  a  fairly  good  opinion  to  be  formed  of  the 
quantity  of  nitric  acid  present.  Suppose  that  the  sample  be 
roughly  estimated  to  contain  about  0.15  part  nitrogen  per  100,000 ; 
in  such  a  case  solutions  of  potassium  nitrate  containing  o.n, 
0.15,  0.19  part  nitrogen  are  selected  from  the  series.  Two  cubic 
centimeters  are  taken  from  each  and  treated,  side  by  side,  with 
a  fresh  quantity  of  the  sample,  precisely  as  described  for  the  pre- 
liminary experiment,  the  various  operations  being  performed  as 
nearly  simultaneously  as  possible  with  each  of  the  samples,  and 
under  precisely  similar  conditions.  Two  or  three  minutes  after 
the  carbazol  has  been  added,  the  intensity  of  the  color  of  each 
is  observed.  If  that  given  by  the  sample  is  matched  by  any  of 
the  standard  solutions,  the  estimation  is  at  an  end.  Similarly,  if 
it  falls  between  two  of  these,  the  mean  may  be  taken  as  repre- 
senting the  nitrogen  present  in  cases  in  which  great  accuracy  is 
not  required.  If  this  be  done,  the  maximum  error  will  be  0.02 
part  nitrogen,  or  0.09  part  nitric  acid  per  100,000.  If  greater 
exactness  be  required,  or  it  be  found  that  the  color  given  by  the 
sample  is  either  darker  or  lighter  than  that  given  by  all  the 
standard  solutions,  a  new  trial  must  be  made.  In  such  a  case 
the  sample  must  be  again  tested  simultaneously  with  the  solu- 
tions with  which  it  is  to  be  compared.  This  is  rendered  neces- 
sary principally  for  the  reason  that  the  shade  of  the  solutions 
to  which  the  carbazol  has  been  added  is  apt  to  change  on  stand- 
ing. Hence  it  is  desirable  that  the  sample,  and  the  standard 
potassium  nitrate  with  which  it  is  to  be  compared,  should  have 
the  carbazol  added  at  as  nearly  the  same  time  as  possible.  When 
finally  the  color  falls  between  that  given  by  any  two  consecutive 
members  of  the  standard  potassium  nitrate  series,  the  estimation 
may  be  considered  at  an  end,  and  the  mean  of  these  solutions 
taken  as  representing  the  nitrogen  present. 

The  greatest  neatness  should  be  observed  in  all  steps  of  the 
analysis.  The  quantity  of  nitric  acid  to  be  estimated  is  so  small 
that  if  the  greatest  care  be  not  exercised  throughout,  sources  of 
error  may  be  readily  introduced.  The  test-tube  should  be  rinsed 
out  with  nitrate-free  water  before  being  used,  and  dried.  The 
tint  is  determined  by  looking  through  the  tube  and  not  through 


460  AGRICULTURAL  ANALYSIS 

the  length  of  the  column  of  liquid.    A  comparison  camera  such 
as  is  described  in  Volume  I,  page  591,  may  be  used  to  advantage. 

Influence  of  Nitrites. — If  the  quantity  of  nitrous  acid  in  the 
water  is  known  a  correction  can  be  applied  for  nitrates  by  deduct- 
ing one-fifth  of  the  number  found  for  nitrites  when  estimated  as 
nitrates. 

Influence  of  Iron. — Although  ferrous  salts  give  no  reaction 
with  carbazol,  nitrates  are  apt  to  be  overestimated  in  their  pres- 
ence. On  the  other  hand,  ferric  compounds,  like  other  oxidiz- 
ing agents,  may  give  a  characteristic  green  color  with  carbazol. 
In  all  cases  when  iron  is  present  in  any  considerable  quantity  it 
is  best  to  remove  it  by  rendering  the  sample  slightly  alkaline, 
evaporating  to  dryness,  and  redissolving  the  soluble  residue 
until  the  solution  reaches  the  original  volume. 

Influence  of  Chlorids. — The  presence  of  chlorids  furnishes  by 
far  the  most  serious  source  of  error  in  the  process  by  intensifying 
the  action  of  the  nitric  acid.  If,  however,  nitrates  be  absent, 
chlorids  give  no  reaction  with  carbazol.  The  chlorids  are  re- 
moved by  the  standard  silver  sulfate  solution,  the  quantity  of 
chlorids  present  having  been  first  determined  by  a  standard  sil- 
ver nitrate  solution.  For  this  purpose  an  ordinary  sugar  flask 
can  be  employed,  marked  at  100  and  no  cubic  centimeters. 
This  flask  is  filled  to  the  100  cubic  centimeter  mark  with  the 
sample  to  be  examined;  the  necessary  quantity  of  silver  sulfate 
is  added  and  then  two  cubic  centimeters  of  the  solution  of  alumi- 
num sulfate,  previously  described,  and  the  contents  of  the 
flask  brought  up  to  no  cubic  centimeters  by  the  addition  of 
pure  distilled  water.  The  whole  is  shaken  up  and  filtered,  the 
first  portion  of  the  filtrate  being  rejected.  The  aluminum  sul- 
fate, by  reacting  with  the  carbonates  usually  present  in  the  water 
and  producing  the  precipitation  of  alumina,  facilitates  the  re- 
moval of  the  precipitated  silver  chlorid. 

The  above  described  method,  on  account  of  its  delicacy,  is  not 
well  suited  to  aqueous  solutions  of  soils  and  fertilizers  except 
where  the  quantity  of  nitric  nitrogen  present  is  extremely  minute. 

Spiegel  also  first  suggested  the  use  of  diphenylamin  for  de- 


METHOD  OF  GILL  461 

tecting  the  presence  of  nitrates,78  a  method  afterwards  worked 
out  by  Hooker.79 

395.  Phenylsulfuric  Acid  Method. — Rideal     also     proposes  a 
variation  of  the  method  described  by  Hooker,  which  consists  in 
the  substitution  of  phenylsulfuric  acid  for  carbazol.80 

The  solutions  required  are: 

(a)  A  standard  solution  of  potassium  nitrate  containing  0.7215 
gram  of  the  pure  crystallized  salt  in  a  liter  of  water. 

(b)  Phenylsulfuric   acid    (acid  phenyl   sulfate),  prepared   by 
dissolving   15  grams  of  pure  crystallized  phenol  in  92.5   cubic 
centimeters  of  pure,  redistilled  sulfuric  acid  free  from  nitrates 
and  diluted  with  seven  and  one-half  cubic  centimeters  of  water. 

The  process  is  conducted  as  follows: 

A  known  volume  of  the  sample,  from  25  to  100  cubic  centi- 
meters, according  to  its  richness  in  nitrates,  is  evaporated  to 
dryness  in  a  porcelain  dish,  one  cubic  centimeter  of  phenylsul- 
furic acid,  one  cubic  centimeter  of  pure  water  and  three  drops 
of  strong  sulfuric  acid  added,  and  the  mixture  gently  warmed. 
A  yellow  color  shows  the  presence  of  nitrates.  Dilute  to  about 
25  cubic  centimeters  with  water  and  add  ammonia  in  slight  ex- 
cess. Pour  into  a  narrow  nessler  tube,  adding  the  washings, 
and  make  up  to  100  cubic  centimeters.  Imitate  the  color  of  the 
solution  with  the  standard  potassium  nitrate  treated  with  the 
same  reagents. 

The  phenylsulfuric  acid  should  be  prepared  some  time  before 
use,  as  the  fresh  solution  imparts  a  greenish  tint  to  the  yellow 
of  the  ammonium  picrate  formed. 

396.  Method  of  Gill. — The  phenyl  sulfate  process,  as  described 
by  Leffman,  is  conducted  as  follows:81 

Solutions  Required. — Acid  phenyl  sulfate  (Phenoldisulfonic 
Acid}  :  Thirty-seven  grams  of  strong  sulfuric  acid  are  added 
to  three  grams  of  pure  phenol  and  heated  for  six  hours  in,  not 
upon  the  water  bath,  and  preserved  in  a  tightly  stoppered  bottle. 

7*  Zeitschrift  fur  Hygiene,  1887,  2  :  163. 

19  Journal  of  the  Franklin  Institute,  1889,  127  :  61. 

80  Chemical  News,  1889,  60  :  261. 

81  Examination  of  Water  for  Sanitary   and   Technical   Purposes,   5th 
Edition,  1903  :  50. 


462  AGRICULTURAL   ANALYSIS 

Standard  potassium  nitrate:  0.722  gram  of  potassium  nitrate, 
previously  heated  to  a  temperature  just  sufficient  to  fuse  it,  is 
dissolved  in  water,  and  the  solution  made  up  to  1000  cubic  centi- 
meters. One  cubic  centimeter  of  this  solution  contains  o.oooi 
gram  of  nitrogen. 

Analytical  Process. — A  measured  volume  of  the  sample  is  evap- 
orated just  to  dryness  in  a  platinum  or  porcelain  basin.  One 
cubic  centimeter  of  the  phenoldisulfonic  acid  is  added  and  thor- 
oughly mixed  with  the  residue  by  means  of  a  glass  rod.  One 
cubic  centimeter  of  water  and  three  drops  of  strong  sulfuric  acid 
are  added,  and  the  dish  gently  warmed.  The  liquid  is  then  di- 
luted with  about  25  cubic  centimeters  of  water,  ammonium  hy- 
droxid  added  in  excess,  and  the  solution  made  up  to  50  cubic 
centimeters. 

The  reactions  are: 

Acid  phenyl  Trinitrophenol 

sulfate.  (picric  acid). 

HC6H5SO4+3HNO3=HC6H2(NO2)3O+H2SO4+2H2O. 

Ammonium  picrate. 

HC6H2(NO2)3O+NH4HO=NH4C6H2(NO2)3O+H2O. 

The  ammonium  picrate  imparts  to  the  solution  a  yellow  color, 
the  intensity  of  which  is  proportional  to  the  amount  present. 

One  cubic  centimeter  of  the  standard  solution  of  potassium 
nitrate  is  similarly  evaporated  in  a  platinum  dish,  treated  as 
above,  and  made  up  to  50  cubic  centimeters.  The  color  pro- 
duced is  compared  to  that  given  by  the  water,  and  one  or  the 
other  of  the  solutions  diluted  until  the  tints  of  the  two  agree. 
The  comparative  volumes  of  the  liquids  furnish  the  necessary 
data  for  determining  the  amount  of  nitrate  present,  as  the  follow- 
ing example  shows: 

One  cubic  centimeter  of  standard  nitrate  is  treated  as  above 
and  made  up  to  100  cubic  centimeters,  representing  o.oooi  gram 
nitrogen. 

Suppose  loo  cubic  centimeters  of  the  sample  similarly  treated 
are  found  to  require  dilution  to  150  cubic  centimeters  before  the 
tint  will  match  that  of  the  standard ;  then 

loo   :  150   ::  o.ooi    :  0.0015 


METHOD   OF   GILL  463 

i.  e.,  the  sample  contains  one  and  one-half  milligrams  of  nitro- 
gen as  nitrate  per  liter. 

The  ammonium  picrate  solution  keeps  very  well,  especially  in 
the  dark.  A  good  plan,  therefore,  is  to  make  up  a  standard  solu- 
tion equivalent  to  10  milligrams  of  nitrogen  as  nitrate  per  liter, 
to  which  the  color  obtained  from  the  sample  may  be  directly 
compared. 

The  results  obtained  by  this  method  are  quite  accurate.  Care 
should  be  taken  that  the  same  quantity  of  phenoldisulfonic  acid  be 
used  for  the  sample  and  for  the  comparison  liquid,  otherwise  dif- 
ferent tints  instead  of  depths  of  tints  are  produced. 

With  subsoil,  fertilized  and  other  solutions  probably  containing 
much  nitrate,  10  cubic  centimeters  of  the  sample  are  sufficient 
for  the  test,  but  with  river  and  spring  waters,  25  to  100  cubic 
centimeters  may  be  used.  When  the  organic  matter  is  sufficient 
to  color  the  residue,  it  will  be  well  to  purify  the  sample  by  addi- 
tion of  aluminum  hydroxid  and  subsequent  filtration,  before 
evaporating.  This  method  may  also  be  used  to  determine  small 
quantities  of  nitrates  when  the  amount  is  too  small  for  estima- 
tion by  the  ferrous  chlorid  or  reduction  processes. 

Mason  calls  attention  to  the  fact  that  chlorids  interfere  with 
the  delicacy  of  the  process,  giving  readings  decidedly  lower 
than  the  truth.82  The  method  is  so  easy  and  convenient,  how- 
ever, that  Mason  was  led  to  add  salt  to  the  comparison  stand- 
ards rather  than  to  abandon  the  process.  In  the  conduct  of  this 
method  the  chlorin  in  the  water  to  be  examined  is  first  to  be 
determined  and  the  standard  solution  is  treated  with  sodium 
chlorid  in  sufficient  quantity  to  afford  the  same  quantity  of 
chlorin  as  in  the  sample.  The  results  are  found  to  be  very  satis- 
factory. If  the  chlorin  be  less  than  10  parts  per  million  it  does 
not  interfere  with  the  determination.  The  solutions  are  pre- 
pared as  follows: 

Phenol-sulfonic  acid — 

Sulfuric  acid,  pure  and  concentrated 370  grams 

Pure  phenol 30  grams 

These  reagents  are  placed  in  a  flask  and  kept  surrounded  by 
88  Examination  of  Water,  3rd  Edition,  1906  =50. 


464  AGRICULTURAL  ANALYSIS 

boiling  water  for  6  hours.  Disulfonic  instead  of  monosulfonic 
acid  is  thus  produced  by  the  prolonged  high  temperature,  and 
this  reacts  readily  upon  the  nitrate. 

Standard  potassium  nitrate — prepared  as  described  above. 

397.  Variation  of  Johnson. — The  ammonium  picrate  method 
has  given  very  satisfactory  results  as  practiced  by  Johnson,  who 
varies  the  process  as  described  below:83 

The  standard  solution  of  potassium  nitrate  is  prepared  by  dis- 
solving 0.7215  gram  of  the  pure  salt  in  a  liter  of  distilled  water, 
and  diluting  100  cubic  centimeters  of  this  solution  to  one  liter 
with  distilled  water.  Ten  cubic  centimeters  of  this  dilute  solu- 
tion contain  nitrogen  equivalent  to  one  part  as  nitrates  in  100,000. 

The  Solution  of  Acid  Phenyl  Sulfate. — This  is  prepared  by 
pouring  two  parts,  by  measure,  of  pure  crystallized  phenol  lique- 
fied by  hot  water  into  five  parts,  by  measure,  of  pure  concentrated 
sulfuric  acid  and  digesting  in  the  water-bath  for  eight  hours. 
After  cooling,  add  one  and  one-half  volumes  of  distilled  water  and 
one-half  volume  of  strong  hydrochloric  acid  to  each  volume  of 
the  above  mixture. 

The  analytical  processes  are  carried  on  as  follows:  Ten  cubic 
centimeters  of  the  sample  or  extract  under  examination  and  10 
cubic  centimeters  of  the  standard  potassium  nitrate  are  placed  in 
small  beakers  and  put  near  the  edge  of  a  hot  plate.  When  nearly 
evaporated  they  are  put  on  the  top  of  the  water-bath  and  left 
there  until  completely  dry.  The  residue,  in  each  case,  is  treated 
with  one  cubic  centimeter  of  the  acid  phenyl  sulfate  and  the 
beakers  placed  on  the  top  of  the  water-bath.  In  an  extract  very 
poor  in  nitric  acid  a  red  color  ought  not  to  appear  for  about  10 
minutes. 

After  standing  about  15  minutes,  the  beakers  are  removed, 
and  the  contents  of  each  washed  successively  into  100  cubic  centi- 
meter flasks ;  about  20  cubic  centimeters  of  0.96  per  cent,  ammo- 
nia are  then  added,  the  100  cubic  centimeters  made  up  by  the 
addition  of  water,  the  yellow  liquid  transferred  to  the  nessler 
glass  and  the  tints  appropriately  compared. 

M  Chemical  News,  1890,  61  :  15. 


ESTIMATION  OF  NITRIC  465 

398.  Estimation  of  Nitric  in  Presence  of  Nitrous  Acid. — The 
detection  of  nitrous  in  presence  of  nitric  acid  can  be  accom- 
plished by  the  method  proposed  by  Griess,  as  described  further 
on,  through  the  development  of  azocolors  with  metaphenylene- 
diamin  and  other  bodies,  which  are  not  produced  under  similar 
conditions  by  nitric  acid.  The  detection  and  estimation  of  nitric 
in  the  presence  of  nitrous  acid,  however,  is  not  so  easy.  Lunge 
and  Lwoff  propose  brucin  for  this  purpose,  which,  contrary  to 
most  authorities,  does  not  give  the  red-yellow  color  with  nitrous 
acid.84  The  reagent  is  prepared  by  dissolving  0.2  gram  of  brucin 
in  100  cubic  centimeters  of  pure  and  concentrated  sulfuric  acid. 
It  is  almost  impossible  to  prepare  a  sulfuric  acid  which  does  not 
give  a  trace  of  color  with  brucin ;  but  with  the  purest  acids  this 
trace  may  be  neglected. 

A  solution  of  nitrate  is  also  prepared  containing  o.oi  milli- 
gram of  nitrogen  as  nitric  acid  in  one  cubic  centimeter.  It  is 
made  by  dissolving  0.0721  gram  of  pure  potassium  nitrate  in  100 
cubic  centimeters  of  distilled  water,  and  diluting  10  cubic  centi- 
meters thereof  with  pure  concentrated  sulfuric  acid  to  100  cubic 
centimeters.  Both  solutions  are  conveniently  preserved  in  burettes 
with  glass  stop-cocks.  The  liquid  to  be  tested  for  nitric  acid 
is  mixed  with  sulfuric  acid  in  such  a  way  that  the  mixture  will 
have  a  specific  gravity  of  1.7.  If  the  liquid  to  be  tested  is  water, 
this  concentration  is  reached  by  adding  three  times  its  volume  of 
the  strong  acid.  For  the  comparison  of  colors,  cylinders  of  color- 
less glass  are  employed,  marked  at  50  cubic  centimeters.  They 
are  about  24  centimeters  high  and  extend  about  10  centimeters 
above  the  mark.  There  is  placed  in  the  cylinder  one  cubic  centi- 
meter of  the  solution  of  nitrate  in  sulfuric  acid,  and  the  same 
quantity  of  the  brucin  mixture,  and  it  is  filled  to  the  mark  with 
pure  sulfuric  acid.  The  contents  of  the  cylinder  are  poured  into 
a  flask  and  warmed  at  from  70° -80°,  until  the  final  yellow  tint 
is  secured,  and  then  poured  into  the  cylinder  again.  The  liquid 
to  be  tested  is  treated  in  exactly  the  same  way.  The  tints  are 
then  equalized  by  pouring  out  a  part  of  the  contents  of  the 
deeper  colored  cylinder,  taking  account  of  the  volume,  and  filling 
up  with  pure  concentrated  sulfuric  acid. 

M  Zeitschrift  fiir  angewandte  chetnie,  1894,  7  :  347- 


4-66  AGRICULTURAL  ANALYSIS 

In  this  manner  the  content  of  nitric  acid  in  the  liquid  under 
examination  can  be  compared  directly  with  the  solution  of  potas- 
sium nitrate  of  known  strength.  The  coloration  is  distinctly  pro- 
duced with  o.oi  milligram  in  50  cubic  centimeters  of  liquid,  at 
least  three-fourths  of  which  must  be  sulfuric  acid. 

399.  Piccini  Process. — The  method  proposed  by  Piccini  may 
also  be  used.85 

About  five  cubic  centimeters  of  the  nitrite  solution  are  placed 
in  a  small  beaker,  some  pure  urea  dissolved  therein  and  a  few 
drops  of  sulfuric  acid,  and  then  held  in  boiling  water  for  three 
minutes.  The  nitrous  acid  is  thus  completely  destroyed.  Ammo- 
nium chlorid  may  be  substituted  for  urea.  The  reaction  is  repre- 
sented by  the  equation,  NH4NO2=N2-}-2H2O.  The  nitric  acid 
present  is  then  determined  by  diphenylamin  or  other  suitable  re- 
agents. Diphenylamin  reacts  both  with  nitrous  and  nitric  acids, 
producing  a  blue  or  violet  tint.  Warington  calls  attention  to  a 
slight  difference,  however,  in  its  deportment  with  these  two  acids. 
When  the  solution  of  the  reagent  is  not  too  strong  a  drop  of  it 
produces  but  little  turbidity  when  added  to  water  or  to  a  solu- 
tion containing  nitric  acid.  When,  however,  nitrous  acid  is  pres- 
ent, a  cream-colored  turbidity  is  produced.  The  violet  color  also 
appears  at  once  on  adding  sulfuric  acid  when  a  nitrite  is  present, 
while  in  the  case  of  nitrates,  more  sulfuric  acid  is  required,  ex- 
cept when  the  solution  is  very  strong.  In  this  connection,  it 
must  not  be  forgotten  that  in  heating  nitrites  with  urea  or  am- 
monium chlorid  in  the  presence  of  a  slight  excess  of  sulfuric  acid, 
a  trace  of  nitric  acid  may  be  formed. 

400.  Colors  Produced  by  Diphenylamin. — In  some  descriptions 
of  the  color  reactions  produced  by  diphenylamin  in  the  presence 
of  nitrates  and  nitrites  and  sulfuric  acid,  the  distinctive  color 
produced  is  described  as  blue.    This  color  is  actually  produced  in 
certain  conditions,  which  are  not  always  easy  to  secure.    Atten- 
tion is  called  to  this  variation  in  tint  in  Volume  I,  page  532.  With 
nitrites,  the  blue  color  is  rather  easily  produced  with  varying 
proportions  of  nitrous  acid,  but  such  is  not  the  case  with  nitrates 

85  Journal  of  the  Chemical  Society,  1891,  59  :  489. 
Gazzetta  chimica  italiana,  1879,  9  :  395. 


METAPHENYLENEDIAMIN    METHOD  467 

and  chlorates.  The  prevailing  colors  developed  with  nitrates  are 
reddish  yellow,  green  and  dirty  violet,  and  with  chlorates,  red- 
brown,  green  and  gray.  The  reactions,  therefore,  as  usually  pro- 
duced are  not  always  reliable,  and  Alvarez  has  proposed  modi- 
fications of  the  process  as  follows  :86 

The  reagent  is  prepared  by  dissolving  o.i  gram  of  diphenyl- 
amin  and  the  same  quantity  of  re-sublimated  resorcin  and  add- 
ing five  or  six  drops  of  the  solution  to  a  fragment  of  the  salt 
to  be  tested  (nitrites,  nitrates  or  chlorates  of  the  alkalies),  placed 
in  a  flat-bottomed  porcelain  capsule. 

The  following  phenomena  are  observed:  With  nitrates  a  very 
permanent  yellowish  green  tint  is  obtained,  and  after  spreading 
out  over  the  surface  of  the  dish  the  edges  of  the  spot  become 
blue.  By  the  addition  of  alcohol  an  orange  color  is  obtained. 
With  nitrites  a  deep  blue  violet  color  is  produced  and  by  moving 
the  liquid  so  as  to  wet  the  whole  interior  of  the  dish,  the  edges 
become  red.  On  adding  alcohol  a  red  color  is  formed.  With 
chlorates  the  results  are  not  satisfactory. 

ESTIMATION  OF  NITROUS  ACID  BY  COLORIMETRIC 
COMPARISON 

401.  Application  of  the  Method. — The  most  minute  traces  of 
nitrous  acid  may  be  detected  by  colorimetric  methods,  and  the 
determination  of  the  quantity  present  may  be  approximated  with 
great  exactness  by  comparison  with  a  solution  of  a  nitrite  of 
known  strength.     Especially  in  following  the  progress  of  nitri- 
fication is  this  method,  in  some  of  its  forms,  of  essential  import- 
ance.   In  delicacy  and  celerity  it  has  the  same  advantages  as  the 
colorimetric  methods   for  the  determination  of  nitric  acid,  and 
the  same  skill  must  be  exhibited  and  the  same  precautions  ob- 
served as  in  the  case  of  nitric  acid  in  order  to  avoid  errors. 

402.  Metaphenylenediamin   Method. — This     process     depends 
upon  the   development   of  a  yellow  color  in   water  containing 
nitrous  acid  on  the  addition  of  a  reagent  containing  metaphenyl- 
enediamin;  (m — CGH4(NH2)2).     This  variety  of  the  phenylene- 
diamins  is  readily  obtained  from  common  dinitrobenzene.  It  melt? 

**  Chemical  News,  1905,  91  :  155. 


AGRICULTURAL  ANALYSIS 

at  63 9  and  boils  at  287°.  In  order  to  preserve  the  reagent  in 
shape  for  use  it  should  be  prepared  in  the  following  manner: 

Dissolve  two  grams  of  the  chlorid  in  10  cubic  centimeters  of 
ammonia,  and  place  the  solution  in  a  glass-stoppered  flask.  To 
this  solution  are  added  five  grams  of  powdered  animal-black,  and 
the  whole  vigorously  shaken.  After  allowing  to  settle,  the  shak- 
ing is  repeated  at  intervals  of  an  hour,  three  or  four  times,  and 
the  flask  then  allowed  to  remain  at  rest  for  24  hours. 

The  supernatant  liquid  is  generally  sufficiently  decolorized  by 
this  treatment.  If  not,  the  shaking  and  subsidence  must  be  re- 
peated until  a  completely  colorless  liquid  is  obtained.  The  solu- 
tion can  be  kept  indefinitely  in  contact  with  the  animal-black. 
Aqueous  and  alcoholic  solutions  of  the  salt  can  not  be  kept. 

The  test  is  made  by  mixing  five  drops  of  the  reagent  with  five 
cubic  centimeters  of  sulfuric  acid.  The  mixture  must  be  color- 
less. To  the- mixture  add  100  cubic  centimeters  of  the  water  or 
solution  to  be  tested,  and  heat  on  the  water  bath  for  five  minutes. 
A  yellow  coloration  indicates  the  presence  of  nitrous  acid. 

The  metaphenylenediamin  test  is  fairly  satisfactory  in  perfectly 
colorless  waters  and  aqueous  extracts.  Many  waters  and  soil 
and  fertilizer  extracts,  however,  have  a  yellowish  tint,  and  this 
interferes  in  a  marked  way  with  a  proper  judgment  of  the  yellow 
triaminazobenzol  developed  in  the  application  of  the  above  test. 

The  decoloration  of  such  waters  by  means  of  sodium  carbonate 
or  aluminum  hydroxid  is  a  matter  of  some  difficulty,  and  not 
wholly  without  action  on  the  nitrites  which  may  be  present.  The 
method,  therefore,  is  inferior  to  the  one  next  described. 

403.  Sulfanilic  Acid  and  Naphthylamin  Test  for  Nitrous  Acid. 
— A  very  delicate  test  for  the  presence  of  nitrous  acid,  first  de- 
scribed by  Griess,  is  the  coloration  produced  thereby  in  an  acid 
solution  of  sulfanilic  acid  and  naphthylamin.87 

87  Berichte  der  deutschen  chemischen  Gesellschaft,  1879,  12  :  426. 
Zeitschrift  fur  analytische  Chemie,  1879,  1 8  :  597. 
Zeitschrift  fur  angewandte  Chemie,  1889,  2  :  666. 
Bulletin  de  la  socie*te*  chimique  de  Paris,  1889,  [3],  2  :  347. 
This  work,  1  :  533. 


TEST  FOR  NITROUS  ACID  469 

Sulfuric  or  acetic  acid  may  be  used  as  the  acidifying  agent, 
preferably  the  latter.  The  solutions  are  prepared  as  follows : 

(1)  Dissolve  one-half  gram  of  sulfanilic  acid  in  150  cubic  cen- 
timeters of  dilute  acetic  acid. 

(2)  Boil  o.i  gram  of  naphthylamin  with  20  cubic  centimeter? 
of  water,  decant  the  colorless  solution  from  the  residue  and  acid- 
ify it  with  150  cubic  centimeters  of  dilute  acetic  acid. 

The  two  solutions  may  at  once  be  mixed  and  preserved  in  a 
well-'stoppered  flask.  The  action  of  light  on  the  mixture  is  not 
hurtful,  but  air-  should  be  carefully  excluded  because  of  the 
traces  of  nitrous  acid  which  it  may  contain.  Whenever  the  mixed 
solutions  show  a  red  tint  it  is  an  indication  that  they  have  ab- 
sorbed some  nitrous  acid.  The  red  color  may  be  discharged  and 
the  solution  again  fitted  for  use  by  the  introduction  of  a  little 
zinc  dust,  and  shaking. 

The  water,  or  aqueous  solution  of  a  soil  or  fertilizer,  to  be 
tested  for  nitrites,  is  treated  in  portions  of  about  20  cubic  centi- 
meters with  a  few  cubic  centimeters  of  the  mixed  reagent  and 
warmed  to  7O°-8o°.  If  nitrous  acid,  in  the  proportion  of  one 
part  to  one  million  be  present,  the  red  color  will  appear  in  a  few 
minutes.  If  the  content  of  nitrous  acid  be  greater,  e.  g.,  one  part 
in  one  thousand,  only  a  yellow  color  will  be  produced,  unless  a 
greater  quantity  of  the  reagent  be  used. 

Leffmann  recommends  the  following  method  of  conducting 
the  determinations  :88 

Solutions  required:  i-^-amidobensenesulfonic  acid  solution 
(sulfanilic  acid). — Dissolve  0.5  gram  in  150  cubic  centimeters 
of  diluted  acetic  acid,  sp.  gr.  1.04. 

a-amidonaphthalene  acetate  solution. — Boil  o.i  gram  of  solid 
a-amidonaphthalene  (a-naphthylamin)  in  20  cubic  centimeters 
of  water,  filter  the  solution  through  a  plug  of  washed  absorbent 
cotton,  and  mix  the  filtrate  with  180  cubic  centimeters  of  dilut- 
ed acetic  acid.  All  water  used  must  be  free  from  nitrites,  and 
all  vessels  must  be  rinsed  out  with  such  water  before  tests  are 
applied,  since  appreciable  quantities  of  nitrites  may  be  taken 
up  from  the  air. 

M  Examination   of   Water   for  Sanitary  and   Technical   Purposes,   5th 
edition,  1903  :  54. 


47O  AGRICULTURAL  ANALYSIS 

Standard  Sodium  Nitrite. — 0.275  gram  pure  silver  nitrite  is 
dissolved  in  pure  water,  and  a  dilute  solution  of  pure  sodium 
chlorid  added  until  the  precipitate  ceases  to  form.  It  is  then 
diluted  with  pure  water  to  250  cubic  centimeters  and  allowed  to 
stand  until  clear.  For  use,  10  cubic  centimeters  of  this  solution 
are  diluted  to  100.  It  is  to  be  kept  in  the  dark. 

One  cubic  centimeter  of  the  dilute  solution  is  equivalent  to 
o.ooooi  gram  of  nitrogen. 

The  silver  nitrite  is  prepared  in  the  following  manner :  A  hot 
concentrated  solution  of  silver  nitrate  is  added  to  a  concentrated 
solution  of  the  purest  sodium  or  potassium  nitrite  available,  fil- 
tered while  hot  and  allowed  to  cool.  The  silver  nitrite  will 
separate  in  fine  needle-like  crystals,  which  are  freed  from  the 
mother-liquor  by  filtration  with  the  aid  of  a  filter  pump.  The  crys- 
tals are  dissolved  in  the  smallest  possible  quantity  of  hot  water, 
allowed  to  cool  and  crystallize,  and  again  separated  by  means  of 
the  pump.  They  are  then  thoroughly  dried  in  the  water  bath,  and 
preserved  in  a  tightly-stoppered  bottle  away  from  the  light.  Their 
purity  may  be  tested  by  heating  a  weighed  quantity  to  redness  in  a 
tared,  porcelain  crucible  and  noting  the  weight  of  the  metallic 
silver.  One  hundred  and  fifty-four  parts  of  silver  nitrite  leave  a 
residue  of  108  parts  of  silver. 

Analytical  Process. — Twenty-five  cubic  centimeters  of  the 
water,  soil  or  fertilizer  solution  are  placed  in  a  color-comparison 
cylinder,  the  measuring  vessel  and  cylinder  having  previously 
been  rinsed  with  the  water  to  be  tested.  By  means  of  a  pipette 
two  cubic  centimeters  each  of  the  test  solutions  are  dropped  in. 
It  is  convenient  to  have  three  pipettes  for  this  test,  and  to  use 
them  for  no  other  purpose.  In  any  case  the  pipette  must  be 
rinsed  out  thoroughly  with  nitrite-free  water  each  time  before 
using,  as  nitrites,  in  quantity  sufficient  to  give  a  distinct  reaction, 
may  be  taken  up  from  the  air. 

One  cubic  centimeter  of  the  standard  nitrite  solution  is  placed 
in  another  clean  cylinder,  made  up  with  nitrite-free  water  to  25 
cubic  centimeters  and  treated  with  the  reagents,  as  above. 

In  the  presence  of  nitrites  a  pink  color  is  produced,  which,  in 
dilute  solutions,  may  require  half  an  hour  for  complete  develop- 


TEST  FOR  NITROUS  ACID  471 

ment.  At  the  end  of  this  time  the  two  solutions  are  compared, 
the  colors  equalized  by  diluting  the  darker,  'and  the  calculation 
made  as  explained  under  the  estimation  of  nitrates. 

The  reactions  consist  in  the  conversion  of  the  sulfanilic  acid 
into  diazobenzenesulfonic  anhydrid,  by  the  nitrite  present;  this 
compound  is  then  in  turn  converted  by  the  amidonaphthalene 
into  azo-a-amidonaphthalene-i-4-benzenesulfonic  acid.  The  last 
named  body  gives  the  color  to  the  liquid. 

The  method  pursued  by  Tanner,  in  the  preparation  of  the 
reagents,  is  as  follows : 

Sulfanilic  acid  is  prepared  by  mixing  30  grams  of  anilin 
slowly,  with  60  grams  of  fuming  sulfuric  acid,  in  a  porcelain 
dish.  The  brown,  sirupy  liquid  formed  is  carefully  heated  until 
quite  dark  in  color,  and  until  the  evolution  of  sulfurous  fumes  is 
noticed.  After  cooling,  the  thick,  semi-fluid  mass  is  poured  into 
half  a  liter  of  cold  water  and  allowed  to  stand  for  some  hours. 
The  liquid  portion  is  decanted  from  the  nearly  black  undis- 
solved  crystalline  mass.  To  the  residue  half  a  liter  of  hot  water 
is  added  and  allowed  to  stand  until  cold,  and  the  liquid  again 
decanted.  The  undissolved  portion  is  treated  with  one  liter  of 
hot  water  and  filtered.  The  filtrate  is  treated  with  animal  char- 
coal to  decolorize  it,  and  allowed  to  stand  for  24  hours  and  again 
filtered,  the  filtrate  diluted  to  1500  cubic  centimeters  and  used  as 
required.  This  solution  tends  to  turn  pink  on  keeping,  and  thus 
its  color  interferes  with  the  delicacy  of  the  test,  and  a  small 
amount  of  animal-char  is  kept  in  a  small  bottle  containing  the 
portion  for  immediate  use,  and  this  bottle  is  filled,  from  time  to 
time,  from  the  larger  one. 

The  solution  of  naphthylamin  hydrochlorate  is  made  with  one 
gram  of  the  salt  dissolved  in  100  cubic  centimeters  of  water. 
The  solution  is  to  be  occasionally  filtered,  and  not  more  than 
100  cubic  centimeters  should  be  prepared  at  a  time. 

The  analytical  operations  are  carried  on  as  follows : 

A  standard  solution  of  pure  potassium  nitrite,  made  from  tht 
silver  salt  in  distilled  water  perfectly  free  from  nitrites,  is  placed 
in  a  color-glass,  similar  to  those  used  in  the  nessler  reaction, 


472  AGRICULTURAL  ANALYSIS 

together  with  a  second  glass  containing  the  water  to  be  tested. 
These  glasses  should  be  marked  to  hold  100  cubic  centimeters  at 
the  same  depth.  To  each  of  the  tubes  a  few  drops  of  pure  hydro- 
chloric acid  are  added  and  two  cubic  centimeters  of  the  sulfanilic 
solution.  Afterwards,  to  each  tube  are  added  two  cubic  centi- 
meters of  the  solution  of  naphthylamin  hydrochlorate,  and  it 
is  allowed  to  stand  for  20  minutes,  at  the  end  of  which  time 
the  color  is  fully  developed.  Each  tube  is  covered  by  a  piece  of 
glass  in  order  to  prevent  access  of  air.  It  is  unnecessary  to  add 
that  the  standard  solutions  of  nitrite  of  different  strength  should 
be  employed  until  the  one  is  found  which  resembles,  as  nearly 
as  possible,  the  color  developed  in  the  sample  of  water  or  extract 
under  examination.  The  application  of  this  test  in  ascertaining 
the  progress  of  nitrification  is  described  in  Volume  I,  page  532. 

404.  Method  of  Mason. — Mason  prefers  the  old  method  of 
using  as  reagents  azobenzolnaphthlamin  sulfonic  acid.89  He 
prepares  his  reagents  as  fallows : 

Sulfanilic  acid. — Dissolve  one  gram  of  the  salt  in  100  cubic 
centimeters  of  hot  water.  The  solution  keeps  well. 

Naphthylamin  hydrochlorid. — Boil  one-half  gram  of  the  salt 
with  100  cubic  centimeters  of  water  for  ten  minutes,  keeping  the 
volume  constant.  Place  in  a  glass  stoppered  bottle.  The  solu- 
tion tends  to  grow  slightly  pink  on  standing,  but  not  sufficient- 
ly so  as  to  interfere  with  its  use. 

Standard  solution  of  sodium  nitrite. — Pure  sodium  nitrite  may 
be  used  but  the  silver  nitrite  as  prepared  above  is  preferred. 

Determination. — To  determine  nitrites  place  100  cubic  centi- 
meters of  the  water  to  be  examined  (decolorized  with  aluminum 
hydrate  if  necessary)  in  a  nessler  tube.  Acidify  with  one  drop 
of  concentrated  HC1.  The  addition  of  too  much  acid  might 
cause  the  nitrates  to  respond  to  the  reaction.  Add  two  cubic 
centimeters  of  the  sulfanilic  acid  solrtion  of  hydrochlorid  of 
naphthylamin,  mix,  cover  with  a  watch  glass,  and  set  aside 
for  30  minutes.  Prepare  at  the  same  time  other  nessler  tubes 
containing  known  amounts  of  the  standard  solution  of  sodium 
nitrite  and  diluted  to  the  TOO  cubic  centimeter  mark  with 
*  Examination  of  water,  3rd  edition,  1906  :  42. 


LUNGE  AND  IAVOFF'S  PROCESS  473 

nitrite-free  distilled  water,  adding  the  reagents  as  above.  At 
the  end  of  the  time  stated  (30  minutes)  examine  the  depth  of 
the  pink  color  formed,  and  by  comparing  the  unknown  with 
the  known  an  accurate  determination  of  the  amount  of  nitrogen 
present  as  nitrites  may  be  made. 

If  much  gas  be  burning  in  the  room,  nitrites  will  be  in  the 
atmosphere.  Hence,  cover  the  tubes  or  remove  them  from  the 
room  during  the  half-hour  interval  before  reading. 

It  may  be  worth  while  to  call  attention  to  the  fact  that  the 
error  due  to  the  presence  of  burning  lamps  is  often  much  great- 
er than  is  suspected.  In  Mason's  water  laboratory  the  pure 
distilled  water  is  prepared  by  the  use  of  a  large  copper  retort 
heated  by  a  very  broad  bunsen  burner.  Only  one  ether  lighted 
burner  is  constantly  in  the  room,  and  that  a  small  one. 

405.  Lunge  and  Lwoff's  Process  for  Nitrous  Acid. — The  re- 
action of  nitrous  acid  with  a-naphthylamin,  first  described  by 
Griess,  may  be  made  reliable,  quantitatively,  by  proceeding  as 
below  :90 

Boil  o.ioo  gram  of  pure  white  a-naphthylamin  for  15  min- 
utes with  loo  cubic  centimeters  of  water,  add  five  cubic  centi- 
meters of  glacial  acetic  acid,  or  its  equivalent  of  dilute  acid,  and 
afterwards  one  gram  of  sulfanilic  acid  dissolved  in  100  cubic  centi- 
meters of  hot  water.  The  mixture  is  kept  in  a  well  closed  flask. 
A  slight  red  tint  in  the  mixture  is  of  no  significance,  inasmuch  as 
this  completely  disappears  when  one  part  of  it  is  mixed  with  50 
parts  of  the  liquid  to  be  examined.  If  the  coloration  be  very  strong 
it  can  be  removed  by  adding  a  little  zinc  dust.  One  cubic  centi- 
meter of  this  reagent  will  give  a  distinct  coloration  with  o.ooi 
milligram  of  nitrous  nitrogen  in  100  cubic  centimeters  of  water. 

The  analysis  is  conducted  in  cylinders  of  white  glass  marked 
at  50  cubic  centimeters.  One  cubic  centimeter  of  the  above 
reagent  is  placed  in  each  of  two  cylinders  with  40  cubic  centi- 
meters of  water  and  five  grams  of  solid  sodium  acetate.  In  one 
of  the  cylinders  is  placed  one  cubic  centimeter  of  a  normal  solu- 
tion of  a  nitrite  prepared  by  dissolving  0.0493  gram  of  pure 
sodium  nitrite  corresponding  to  10  milligrams  of  nitrogen  in  100 
cubic  centimeters  of  water,  and  adding  10  cubic  centimeters  of 
»°  Zeitschrift  fur  angewandte  Chemie,  1894,  7  :  349- 


474  AGRICULTURAL  ANALYSIS 

this  solution  to  90  cubic  centimeters  of  pure  sulfuric  acid. 
This  secures  a  normal  solution  of  nitrosylsulfuric  acid,  of  which 
each  cubic  centimeter  corresponds  to  o.oi  milligram  of  nitrogen. 

In  the  other  cylinder  is  placed  one  cubic  centimeter  of  the 
solution  to  be  examined,  and  the  contents  of  both  cylinders  are 
well  mixed  so  that  the  nitrous  acid  in  a  nascent  state  may  act  on 
the  reagent.  The  colors  are  compared  after  any  convenient 
period,  but,  as  a  rule,  after  five  minutes. 

The  chief  improvement  made  by  Lunge  and  Lwoff  on  the 
method  of  Griess  is  in  keeping  the  reagent  in  a  mixed  state 
ready  for  use,  by  means  of  which  any  nitrous  impurities  in  the 
components  thereof  are  surely  indicated.  Its  advantage  over 
the  method  of  Ilosvay  consists  in  using  the  comparative  normal 
nitrite  solution  as  nitrosylsulfuric  acid,  in  which  state  it  is  much 
more  stable.91 

406.  Estimation   of  Nitrous   Acid   with    Starch   as    Indicator. 
— The  method  of  procedure,  depending  on  the  blue  color  pro- 
duced in  a  solution  of  starch  in  presence  of  a  nitrite  and  zinc  iodid, 
when  treated  with  sulfuric  acid,  is  not  of  wide  application  on  ac- 
count of  the  interference  produced  by  organic  matter.     The  soil 
or  fertilizer  extract  or  water  is  treated  in  a  test-tube,  with  a  few 
drops  of  starch  solution  and  some  zinc  iodid,  to  which  is  added 
some  sulfuric  acid.     The  decomposition  of  the  nitrite  is  attended 
with  the  setting  free  of  an  equivalent  amount  of  iodin  which  gives 
a  blue  coloration  to  the  starch  solution.     The  depth  of  the  tint  is 
imitated  by  treating  a  standard  solution  of  nitrite  in  a  similar 
way  until  the  proper  quantity  is  found,  which  gives  at  once  the 
proportion  of  nitrite  in  the  sample  examined.     This  process,  how  • 
ever,  is  scarcely  more  than  a  qualitative  one. 

407.  Estimation  of  Nitrites  by  the  Method   of  Chabrier. — In 
order  to  make  the  estimation  of  the  evolved  nitrous  acid  more 
definite  by  the  iodin  method,  Chabrier  has  elaborated  a  plan  for 
titrating  it  with  a  reducing  agent.92 

The  substance  chosen  for  this  purpose  is  sodium  hyposulfite. 
In  point  of  fact,  it  is  not  the  nitrous  acid  which  is  attacked  by 

91  Bulletin  de  la  Soci^te"  chimique  de  Paris,  1894,  [3],  11  :  218. 
91  Encyclopedic  chimique,  1888,  4  :  262. 


ESTIMATION    OF    NITRITES 


475 


the  hyposulfite,  but  the  equivalent  amount  of  free  iodin  repre- 
senting it.  In  the  case  of  a  soil  or  fertilizer  where  the  quantity 
of  nitrites  is  usually  very  small,  it  is  well  to  use  as  much  as  one 
kilogram  for  making  the  extract.  The  extraction  should  be  made 
rapidly,  with  water  free  of  nitrites,  in  order  to  avoid  any  reducing 
action  on  the  nitrates  which  may  be  present.  In  the  case  of  water, 


Figure  37.    Apparatus  of  Chabrier. 

from  five  to  10  liters  should  be  evaporated  to  a  small  volume.  The 
concentration  should  take  place  in  a  large  flask,  rather  than  in  an 
open  dish,  in  order  to  avoid  any  possibility  of  the  absorption  of 
nitrites  produced  by  combustion  in  the  flame  of  the  burner.  When 
the  volume  has  been  reduced  to  about  100  cubic  centimeters, 
it  is  transferred  to  a  small  flask  and  the  concentration  con- 
tinued until  only  10  or  15  cubic  centimeters  are  left.  The  residue 
is  filtered  into  a  woulff  bottle,  shown  in  Fig.  37,  of  about  100 
cubic  centimeters  capacity. 


476  AGRICULTURAL  ANALYSIS 

One  of  the  side  tubules  carries  a  burette,  containing  five  per 
cent,  sulfuric  acid,  the  other  one  is  filled  with  a  hyposulfite  solution 
of  known  strength.  The  middle  tubule  serves  to  introduce  a 
glass  tube  through  which  carbon  dioxid  or  illuminating  gas 
passes  for  the  purpose  of  driving  out  the  air  from  the  solution 
and  the  flask.  If  carbon  dioxid  be  used  it  should  be  generated 
by  the  action  of  sulfuric  acid  on  marble.  The  cork  holding 
this  is  furnished  with  a  slot  or  valve  to  permit  the  exit  of  the 
air  and  the  excess  of  the  gas. 

Before  inserting  the  middle  stopper,  a  few  cubic  centimeters 
of  potassium  iodid  solution  and  a  few  drops  of  thin  starch  paste 
are  added,  the  potassium  salt  being  always  used  in  excess  of 
the  nitrite  supposed  to  be  present. 

After  the  air  has  all  been  expelled  from  the  flask,  the  ana- 
lytical process  is  commenced,  the  carbon  dioxid  current  being 
slowly  continued.  At  first,  a  few  drops  of  the  dilute  sulfuric 
acid  are  allowed  to  flow  into  the  flask.  As  soon  as  the  liquid  is 
colored  blue,  a  sufficient  quantity  of  the  thiosulfate  solution  is 
added  to  discharge  the  color.  The  successive  addition  of  acid 
and  thiosulfate  is  continued  until  another  portion  of  the  acid 
fails  to  develop  the  blue  color,  thus  indicating  that  all  the  nitrite 
has  been  decomposed.  From  the  volume  of  thiosulfate  used,  the 
quantity  of  nitrite  is  calculated. 

The  Thiosulfate  Solution. — The  thiosulfate  solution  is  con- 
veniently prepared,  when  a  large  number  of  analyses  is  to  be 
made,  by  dissolving  25  grams  of  pure  crystallized  sodium  thio- 
sulfate in  loo  cubic  centimeters  of  water  and  diluting  any  con- 
venient part  thereof  to  100  or  1000  cubic  centimeters,  accord- 
ing to  the  supposed  strength  of  nitrite  solution  under  examination. 

For  fixing  the  strength  of  the  solution  dissolve  3.348  grams  of 
pure  iodin  in  a  solution  of  potassium  iodid  and  make  the  volume 
up  to  one  liter.  Each  cubic  centimeter  of  this  solution  corre- 
sponds to  one  milligram  of  nitrous  acid.  A  given  volume  of  the 
iodin  solution  is  titrated  against  the  thiosulfate,  but  it  is  best 
not  to  add  the  starch  paste  until  the  greater  part  of  the  iodin  has 
been  removed.  The  starch  paste  is  then  added  and  the  titra- 
tion  continued  until  the  blue  color  has  been  discharged.  Ten 


ESTIMATION   OF   NITROUS  ACID  477 

cubic  centimeters  of  the  iodin  solution  is  a  convenient  quantity 
for  the  titration  and  the  thiosulfate  should  be  diluted  by  adding 
to  10  cubic  centimeters  of  the  solution  mentioned  above,  990 
cubic  centimeters  of  water.  Each  liter  of  this  dilute  solution 
contains  two  and  a  half  grams  of  the  sodium  thiosulfate. 

Example. — Suppose  that  it  has  required  21.3  cubic  centimeters 
of  thiosulfate  to  absorb  10  cubic  centimeters  of  the  iodin  solu- 
tion; further,  that  10  liters  of  water  have  been  evaporated  and 
titrated  as  described  above,  and  that  the  volume  of  thiosulfate 
employed  is  13.8  cubic  centimeters.  From  this  is  derived  the 

following  formula :  — —          -  =  6.48  milligrams  of  nitrous  acid  ; 

or  0.648  milligram  per  liter. 

408.  Estimation  of  Nitrous  Acid  by  Coloration  of  Solution  of 
Ferrous  Salt. — This  method,  due  to  Piccini,  is  based  on  the  pro- 
duction of  the  well-known  brown  color  formed  by  the  action  of 
nitric  oxid  on  a  ferrous  salt.93     The  nitrite  is  decomposed  by 
heating  with  acetic  acid  while  nitrates  thus  treated  do  not  develop 
the  reaction.  The  tint  produced  is  imitated,  as  above,  by  testing 
against  a  standard  solution  of  nitrite.     Ferrous  chlorid  is  to  be 
preferred  to  other  ferrous  salts  for  the  above  purpose.   The  pro- 
cess should  be  carried  on  in  solutions  free  of  air. 

VOLUMETRIC  METHOD  FOR  NITROUS  ACID 

409.  Estimation  of  Nitrous  Acid  by  Decomposition  with  .Potas- 
sium Ferrocyanid. — The  method  of  Schaeffer  was  first  described 
in  1851,  but  little  attention  has  been  paid  to  it  since.  The  method 
was  brought  into  notice  again  by  Deventer:94 

The  reaction  depends  upon  the  decomposition  of  nitrous  acid 
by  potassium  ferrocyanid  in  the  presence  of  acetic  acid  with  the 
formation  of  potassium  ferricyanid  and  acetate,  and  nitric  oxid. 
The  reaction  is  expressed  by  the  following  equation: 

2K4FeCy0-f2HNO2+2C2H4O2 
=K6Fe2Cy12+2KC2H3O2+2NO+2H2O. 
A  eudiometer  with  a  glass  stop-cock  is  arranged  as  shown  in 

93  p^Hgot,  Trait^  de  Chimie  analytique  appliqu£e  &  1' Agriculture,  1883  : 
261. 

94  Berichte  der  deutschen  chemischen  Gesellschaft,  1893,  26  :  589. 


AGRICULTURAL,   ANALYSIS 


Fig.  38.  The  lower  part  of  the  eudiometer  is  closed  with  a  rub- 
ber stopper  carrying  a  glass  tube  which  ends  in  the  pan  /  as 
shown  at  e.  The  eudiometer  is  filled  to  the  stop-cock  with  a 
solution  of  potassium  ferrocyanid  of  about  14  per  cent,  strength. 
The  dish  /  is  also  filled  up  to  the  height  indicated  in  the  figure 
with  the  same  solution.  The  solution  of  nitrite  is  used  in  such 


Figure  38.     Schaeffer's  Nitrous  Acid  Method. 

quantities  that  the  nitric  oxid  evolved  will  occupy  a  space  of  about 
20  cubic  centimeters.  The  whole  eudiometer  should  contain 
about  57  cubic  centimeters.  The  nitrite  solution  is  added  to  the 
eudiometer  by  means  of  a  funnel  a.  The  vessel  containing  it  is 
washed  out  with  a  little  water  and  with  acetic  acid  and  finally 
with  a  few  cubic  centimeters  of  strong  potassium  ferrocyanid  so- 
lution. The  last  fluid  flows  through  the  solution  of  nitrite  and 
acetic  acid  and  thus  mixes  it  with  the  solution  already  in  the 
eudiometer.  The  liquids  reacting  on  each  other  float  together  on 
the  strong  ferrocyanid  solution  and  each  one  of  them  is  at  once 
pressed  downward  by  the  gases  which  are  evolved.  When  the 
evolution  of  gas  becomes  slower  the  apparatus  should  be  shaken 


COLLECTING  SAMPLES  OF  RAIN  WATER  479 

for  about  20  minutes,  moving  it  back  and  forth  without  taking  the 
bottom  of  it  out  of  the  dish.  When  there  is  no  longer  any  evolu- 
tion of  gas,  water  is  added  through  a  slowly,  until  the  heavy  potas- 
sium ferrocyanid  solution  is  almost  completely  driven  out  of  the 
eudiometer.  The  opening  of  the  tube  at  e  is  then  closed  with  the 
thumb,  the  apparatus  is  taken  out  of  the  dish,  shaken  for  some 
time  in  a  vertical  direction  and  again  placed  in  the  dish.  Water 
of  any  required  temperature  is  now  allowed  to  flow  through  the 
jacket  gh,  until  the  temperature  is  constant,  when  the  volume 
of  nitric  oxid  is  read.  The  whole  experiment  can  be  performed 
in  less  than  an  hour.  Operating  in  this  way,  at  the  end  there 
is  in  the  eudiometer  a  liquid  which  is  not  very  different  from 
water  and  one  whose  coefficient  of  solubility  for  nitric  oxid 
is  practically  the  same  as  that  of  water.  The  gas  volume  read  is 
to  be  corrected  for  temperature,  pressure,  tension  of  the  aqueous 
vapor,  height  of  the  water  column  in  the  eudiometer,  and,  after 
the  end  of  the  calculation,  five  per  cent,  of  the  volume  of  water 
remaining  in  the  eudiometer  is  to  be  added  to  the  volume  of  gas 
obtained.  This  is  to  compensate  for  the  volume  of  the  gas 
absorbed  by  the  water.  The  method  gives  good  quantitative  re- 
sults. 

410.  General  Observations. — The  determination  of  nitrous  acid 
in  itself  is  of  little  interest  in  fertilizer  examinations.     It  exists 
in  fertilizers  only  in  negligible  quantities.     Its  determination  is  of 
greater  importance  in  sanitary  water  analysis  than  in  fertilizer 
control.     It  is  of  some  importance,  however,  in  connection  with 
the  occurrence  of  nitric  acid,  and  this  fact  warrants  the  space 
which  has  been  given  to  its  discussion. 

411.  Method  of  Collecting  Samples  of  Rain  Water  for  Analysis. 
— In  pot  and  field  experiments  with     fertilizers     the    study     of 
the  drainage  waters  is  of  supreme  importance.     For  this  reason 
the  methods  for  determining  nitrous  and  nitric  acids  have  been 
given   in  detail.     The  collection  of  the  drainage  waters  is  an 
important  factor  of  this  study.    Warington  collects  rain  water  in 
a  large  leaden  gauge  having  an  area  of  o.ooi  of  an  acre.95     Of 
the  daily  collection  of  rain,  dew  and  snow  water,  an  aliquot 

95  Journal  of  the  Chemical  Society,  1889,  55  :537- 


480  AGRICULTURAL  ANALYSIS 

part,  amounting  to  a  gallon  for  each  inch  of  precipitation,  is 
placed  in  a  carboy;  at  the  end  of  each  month  the  contents  of 
the  carboy  are  mixed,  and  a  sample  removed  for  analysis.  In 
the  carboy,  receiving  the  rain  for  nitric  acid  estimation,  a  little 
mercuric  chlorid  is  placed  each  month  with  the  view  of  pre- 
venting any  change  of  ammonia  into  nitric  acid.  It  may  be 
doubted,  however,  if  this  precaution  is  necessary,  as  the  rain 
water  thus  collected  always  contains  a  very  appreciable  amount 
of  lead;  and  experiments  have  shown  that  on  the  whole  rain 
water  more  frequently  gains  than  loses  ammonia  by  keeping. 

Preparation  of  the  Sample. — The  method  first  employed  by 
Warington  was  to  concentrate  10  pounds  of  the  rain  water  in  a 
retort,  a  little  magnesia  being  used  to  decompose  any  ammonium 
nitrite  or  nitrate  present.  Concentration  by  evaporation  in  the 
open  air,  and  especially  over  gas,  results  in  a  distinct  addition 
to  the  nitrites  present.  When  concentrated  to  a  small  bulk,  the 
water  is  filtered  and  evaporated  to  dryness  in  a  very  small  beaker. 
The  nitrogen,  as  nitrates  and  nitrites,  is  then  determined  by 
the  methods  already  described. 

DETERMINATION  OF  FREE   AND   ALBUMINOID    AMMONIA 

IN  RAIN  AND  DRAINAGE  WATERS  AND 

SOIL  AND  FERTILIZER  EXTRACTS 

412.  Nessler  Process. — The  quantities  of  free  ammonia  in 
rain  and  most  drainage  waters  are  minute,  but  may  reach  con- 
siderable magnitude  in  some  sewages.  By  reason  of  these  mi- 
nute proportions,  gravi-  and  volumetric  methods  are  not  suita- 
ble for  its  quantitative  determination.  Recourse  is,  therefore, 
had  to  the  delicate  colorimetric  reaction  first  proposed  by  Ness- 
ler. This  reaction  is  based  on  the  yellowish  brown  coloration 
produced  by  ammonia  in  a  solution  of  mercuric  iodid  in  potas- 
sium iodid.  The  coloration  is  due  to  the  formation  of  oxydi- 
mercuric  ammonium  iodid,  NH2Hg2OI,  and  the  reaction  takes 
place  between  the  molecule  of  free  ammonia  and  the  mercuric 
iodid  dissolved  in  the  alkaline  potassium  iodid  as  represented  by 
the  following  equation: 

/Hg-O-Hg— I  /Hg, 

O<  +  2H3N  =  2O<         >NH2I  +  H2O. 

\Hg-0-Hg-I  \Hg/ 


NESSLER   PROCESS  481 

Nessler  Reagent. — Dissolve  35  grams  of  potassium  iodid  in 
100  cubic  centimeters  of  water.  Add  gradually  to  this  solu- 
tion, a  solution  of  17  grams  of  mercuric  chlorid  in  300  cubic  centi- 
meters of  water  until  a  permanent  precipitate  of  mercuric  iodid 
is  formed.  Add  enough  of  a  20  per  cent,  solution  of  sodium 
hydroxid  to  make  1000  cubic  centimeters. 

The  mixed  solutions,  at  room  temperature,  are  treated  with 
additional  mercuric  chlorid  until  the  precipitate  formed,  after 
thorough  stirring,  remains  undissolved.  This  precipitate  is  al- 
lowed to  subside,  and  when  the  supernatant  liquid  is  perfectly 
clear,  it  is  decanted  or  filtered  through  asbestos  and  kept  in  a 
well-stoppered  bottle  in  a  dark  place.  The  part  in  use  should 
be  transferred  to  a  smaller  bottle  as  required.  The  solution 
should  be  made  for  a  few  days  before  using,  since  its  delicacy  is 
increased  by  keeping.  The  nessler  reagent  should  show  a  faint 
yellow  tint.  If  colorless  it  is  not  delicate,  and  shows  the  addi- 
tion of  an  insufficient  quantity  of  mercuric  chlorid.  When 
properly  prepared,  two  cubic  centimeters  of  the  reagent  poured 
into  50  cubic  centimeters  of  water  containing  0.05  milligram  of 
ammonia  will  at  once  develop  a  yellowish  brown  tint. 

Preparation  of  Ammonia-Free  Water. — To  pure  distilled 
water  add  pure,  recently-ignited  sodium  carbonate,  from  one  to 
two  grams  per  liter,  and  distil.  When  one-fourth  of  the  whole 
has  passed  over,  the  distillate  may  be  regarded  as  free  from  am- 
monia, and  50  cubic  centimeters  of  the  following  distillate  should 
give  no  reaction  with  the  nessler  reagent.  The  distillation  is 
continued  until  the  residual  volume  in  the  retort  is  about  one- 
fourth  of  the  original,  and  the  distillate  free  of  ammonia  is  care- 
fully preserved  in  close  glass-stoppered  bottles  previously  washed 
with  ammonia-free  water.  Pure  water,  free  of  ammonia,  may 
also  be  obtained  by  distilling  with  sulfuric  acid. 

Comparative  Solution  of  Ammonium  Chlorid  Containing 
o.ooooi  Gram  Ammonia  in  One  Cubic  Centimeter. — Dissolve  3.15 
grams  H4NC1  in  ammonia-free  water  and  make  the  volume  up  to 
one  liter.  Dilute  10  cubic  centimeters  of  the  above  solution  to 
1000  with  water,  free  from  ammonia. 

Solution   Containing   o.ooooi   Gram   Nitrogen   in   One   Cubic 
16 


482 


AGRICULTURAL  ANALYSIS 


Centimeter. — Dissolve  3.82  grams  H4NC1  in  water,  free  from  am- 
monia and  dilute  to  1000  cubic  centimeters.  Dilute  10  cubic 
centimeters  of  the  above  solution  to  1000. 

The  Distillation. — Any  kind  of  suitable  retort   or  flask  con- 


Fig.  39.    Water  Distilling  Apparatus,  Bureau  of  Chemistry. 

nected  with  a  good  condenser  may  be  used.     The  capacity  of 
the  retort  should  be  from  700  to  1000  cubic  centimeters.     The 


PROCESS  483 

retorts  and  condensers  used  by  the  water  laboratory  of  the  Bu- 
reau of  Chemistry  are  shown  in  Fig.  39.  The  retorts  having 
been  previously  rinsed  with  distilled  water,  receive  500  cubic 
centimeters  of  the  liquid  to  be  tested  for  ammonia,  together  with 
a  few  pieces  of  recently  ignited  pumice  stone,  to  prevent  bump- 
ing, and  five  cubic  centimeters  of  the  20  per  cent, 
sodium  carbonate  solution  to  render  the  contents  alka- 
line. The  water  is  raised  to  the  boiling-point  and  with  gentle 
ebullition  50  cubic  centimeters  of  distillate  collected.  The  dis- 
tillate is  conveniently  collected  in  a  color-comparison  cylinder 
of  thin  white  glass  and  flat  bottom,  about  two  and  a  half  centi- 
,  meters  in  diameter,  and  marked  at  50  and  100  cubic  centimeters. 
Two  cubic  centimeters  of  the  nessler  reagent  are  added,  and  if 
ammonia  be  present  a  yellowish-brown  color  will  be  developed, 
the  intensity  of  which  is  matched  by  taking  portions  of  the  am- 
monium chlorid  solution,  diluting  to  50  cubic  centimeters  with 
pure  water  and  treating  with  the  same  quantity  of  the  nessler 
reagent.  The  process  is  repeated  until  a  distillate  is  obtained 
which  gives  no  reaction  for  ammonia.  The  sum  of  the  quan- 
tities obtained  in  the  several  distillates  gives  the  total  amount 
of  ammonia  in  the  500  cubic  centimeters  of  the  water.  In  most 
cases  practically  all  the  ammonia  is  obtained  in  three  or  four 
portions  of  the  distillate. 

Albuminoid  Ammonia. — The  residue  from  the  process  just 
described  is  employed  for  the  purpose  of  determining  the  albu- 
minoid ammonia.  Two  hundred  grams  of  potassium  hydroxid 
and  eight  grams  of  potassium  permanganate  are  dissolved  in 
1000  parts  of  distilled  water.  Fifty  cubic  centimeters  of  the 
solution  are  placed  in  a  porcelain  dish  with  100  cubic  centimeters 
of  distilled  water  and  evaporated  to  50  cubic  centimeters.  This 
liquid  is  placed  in  the  retort  and  the  distillation  resumed  and 
continued  until  an  ammonia-free  distillate  is  obtained.  The  total 
albuminoid  ammonia  is  determined  by  taking  the  sum  of  the 
quantities  in  the  several  distillates. 

Mason  varies  the  nesslerizing  process  from  the  above  in  the 
following  detail  :96 

M  Examination  of  Water,  3rd  Edition,  1906  :  56. 


AGRICULTURAL  ANALYSIS 

Preparation  of  the  Nessler  Solution. — Sixteen  grams  of  mer- 
curic chlorid  are  dissolved  in  about  one-half  liter  of  pure  water 
and  35  grams  of  potassium  iodid  in  about  200  cubic  centimeters 
of  pure  water  and  the  first  solution  is  poured  slowly  into  the 
second  until  a  slight  excess  is  indicated  by  the  appearance  of  a 
color  or  a  precipitate.  To  the  mixture  are  added  160  grams  of 
solid  potassium  hydrate,  and  when  this  is  dissolved,  the  volume  is 
made  up  to  one  liter.  A  strong  solution  of  mercuric  chlorid  is 
added  little  by  little  until  the  red  mercuric  iodid  which  is  formed 
is  not  redissolved.  The  precipitate  should  not  be  removed  by 
filtration  but  allowed  to  subside,  and  the  completed  reagent 
shows  a  pale  straw  color.  The  reaction  which  takes  place  in 
the  presence  of  ammonia  is  represented  as  follows : 


(22KI,    HgI2)+NH8+3KOH=NHgJH2O+7KI+2H2O. 

Pure  Water. — Mason  prepares  pure  water  in  a  live  gallon  cop- 
per retort  using  good  spring  water  which  is  treated  with  a 
few  crystals  of  potassium  permanganate  and  subjected  to  dis- 
tillation until  50  cubic  centimeters  when  nesslerized  give  no 
brown  color  in  10  minutes.  The  distillation  should  not  be  push- 
ed too  far  otherwise  ammonia  may  be  generated  from  any  or- 
ganic matter  which  may  be  present  in  the  water. 

413.  Nessler  Reagent  of  Ilosvay. — To  secure  greater  delicacy 
in  nesslerizing,  Ilosvay  uses  a  reagent  prepared  as  follows  :97 

Dissolve  two  grams  of  potassium  iodid  in  five  cubic  centi- 
meters of  water,  heat  the  solution  gently,  and  add  three  grams 
of  mercuric  iodid.  After  the  solution  is  cooled,  add  another 
portion  of  three  grams  of  the  mercury  salt,  and  then  20 
cubic  centimeters  of  water,  and  wait  until  the  precipitation  is 
complete.  After  filtering,  there  are  added  to  the  filtrate  from  20 
to  30  cubic  centimeters  of  a  20  per  cent,  solution  of  potassium 
hydroxid.  Only  the  limpid  supernatant  liquid  is  used  in  the 
analytical  work.  With  this  reagent,  Ilosvay  has  been  able  to  de- 
tect 0.02  milligram  of  ammonia  in  1 10  cubic  centimeters  of  water. 


97  Bulletin  de  la  Soci£te  chimique  de  Paris,  1894,  [3],  11  :  216. 


PART  THIRD 


POTASH  IN  FERTILIZING  MATERIALS  AND 
FERTILIZERS 

414.  Introduction. — The  potash  present  in  unfertilized  soils 
has  been  derived  from  the  decay  of  rocks  containing  potash  min- 
erals. Among  these  potash  producers  feldspars  are  perhaps  the 
most  important.  For  a  discussion  of  the  nature  of  their  decom- 
position and  the  causes  producing  it,  the  first  part  of  Volume  I 
may  be  consulted.  Potash  is  quite  as  extensively  distributed  as 
phosphoric  acid,  and  no  true  soils  are  without  it  in  some  propor- 
tion. Its  presence  is  necessary  to  plant  growth  and  it  forms,  in 
combination  with  organic  and  mineral  acids,  an  essential  part  of 
the  vegetable  organism,  existing  in  exceptionally  rich  quantities 
in  the  seeds.  It  is  possible  that  potash  salts,  such  as  the  chlorid. 
sulfate,  and  phosphate,  may  be  assimilated  as  such,  but,  as  with 
other  compounds,  we  must  not  deny  to  the  plant  the  remarkable 
faculty  of  being  able  to  decompose  its  most  stable  salts  and  to 
form  from  the  fragments  thus  produced  entirely  new  compounds. 
This  is  certainly  true  of  the  potash  compounds  existing  in  plants 
in  combination  with  organic  acids.  The  potash  which  is  assim- 
ilated by  plants  exists  in  the  soil  chiefly  in  a  mineral  state,  and 
that  added  as  fertilizer  is  chiefly  in  the  same  condition.  That 
part  of  the  potash  in  a  soil  arising  directly  from  the  decomposi- 
tion of  vegetable  matters  may  exist  partly  in  organic  combina- 
tion, but  this  portion,  in  comparison  with  the  total  quantity  ab- 
sorbed by  the  plant,  is  insignificant. 

It  is  then  safe  to  assume  that  at  least  a  considerable  part  of 
the  potash  absorbed  by  the  plant  is  changed  from  its  original 
form  of  combination  by  the  vegetable  biochemical  forces,  and  is 
finally  incorporated  in  the  plant  tissues  in  forms  determined  by 
the  processes  of  vegetable  metabolism. 

The  analyst  is  not  often  called  upon  to  investigate  the  forms 


486  AGRICULTURAL,  ANALYSIS 

in  which  the  potash  exists  in  plants,  when  engaged  in  investiga- 
tion of  fertilizers.  It  is  chiefly  found  in  combination  with  or- 
ganic and  phosphoric  acids,  and  on  ignition  will  appear  as  phos- 
phate or  carbonate  in  the  ash. 

POTASH  IN  MINERAL  DEPOSITS 

415.  Occurrence  and  History. — The  generally  accepted  the- 
ories of  the  manner  in  which  potash  has  been  collected  into  de- 
posits suited  to  use  as  a  fertilizer  are  described  below. 

The  most  extensive  potash  deposits  known  are  those  in  the 
neighborhood  of  Stassfurt,  in  Germany.  The  following  descrip- 
tion probably  represents  the  method  of  formation  of  these  de- 
posits :98 

The  Stassfurt  salt  and  potash  deposits  had  their  origin,  thou- 
sands of  years  ago,  in  a  sea  or  ocean,  the  waters  of  which  grad- 
ually receded,  leaving  near  the  coast,  lakes  which  still  retained 
communication  with  the  great  ocean  by  means  of  small  channels. 
In  that  part  of  Europe  the  climate  was  then  tropical,  and  the 
waters  of  these  lakes  rapidly  evaporated,  but  were  constantly  re- 
plenished through  these  small  channels  connecting  them  with 
the  main  body.  Decade  after  decade  this  continued,  until  by 
evaporation  and  crystallization  the  various  salts  present  in  the 
sea  water  were  deposited  in  solid  form.  The  less  soluble  material, 
such  as  sulfate  of  lime  or  "anhydrite,"  solidified  first  and  formed 
the  lowest  stratum.  Then  came  common  rock  salt,  with  a  slowly 
thickening  layer  which  ultimately  reached  3000  feet,  and  is  esti- 
mated to  have  been  13,000  years  in  formation.  This  rock  salt 
deposit  is  interspersed  with  lamellar  deposits  of  "anhydrite," 
which  gradually  diminish  towards  the  top  and  are  finally  re- 
placed by  the  mineral  "polyhalit,"  which  is  composed  of  sul- 
fate of  lime,  sulfate  of  potash,  and  sulfate  of  magnesia.  The 
situation  in  which  this  polyhalit  predominates  is  called  the 
"polyhalit  region,"  and  after  it  comes  the  "kieserit  region,"  in 
which,  between  the  rock  salt  strata,  kieserit  (sulfate  of  mag- 
nesia) is  embedded.  Above  the  kieserit  lies  the  "potash  region," 
consisting  mainly  of  deposits  of  carnallit,  a  mineral  compound 
96  Potash,  Published  by  the  German  Kali  Syndicate,  1906. 


OCCURRENCE   AND   HISTORY  487 

of  chlorids  of  potash  and  magnesia.  The  carnallit  deposit  is 
from  50  to  130  feet  thick  and  yields  the  most  important  of  the 
crude  potash  salts  and  that  from  which  are  manufactured  most 
of  the  concentrated  articles,  including  muriate  of  potash. 

Overlying  this  region  is  a  layer  of  impervious  clay  which  acts 
as  a  water-tight  roof  to  protect  and  preserve  the  very  soluble 
potash  and  magnesia  salts,  which,  had  it  not  been  for  the  pro- 
tection of  this  overlying  stratum,  would  have  been  long  ages 
ago  washed  away  and  lost  by  the  action  of  the  water  percolating 
from  above.  Above  this  clay  roof  is  a  stratum  of  varying  thick- 
ness of  anhydrite,  and  still  above  this  is  a  second  salt  deposit, 
piobably  formed  under  more  recent  climatic  and  atmospheric 
influences  or  possibly  by  chemical  changes  resulting  in  dissolv- 
ing and  subsequent  precipitation  of  the  compounds.  This  salt 
deposit  contains  98  per  cent,  (often  more)  of  pure  salt,  a  degree 
of  purity  rarely  elsewhere  found.  Finally,  above  this  are  strata 
of  gypsum,  tenacious  clay,  sand  and  limestone,  which  crop  out 
at  the  surface. 

The  perpendicular  distance  from  the  lowest  to  the  upper  sur- 
face of  the  Stassfurt  salt  deposits  is  about  5000  feet  (a  little  less 
than  a  mile),  while  the  horizontal  extent  of  the  bed  is  from  the 
Harz  Mountains  to  the  Elbe  River  in  one  direction,  and  from 
the  city  of  Magdeburg  to  the  town  of  Bernburg  in  the  other. 

According  to  Fuchs  and  de  Launay  the  saline  formation  near 
Stassfurt  is  situated  at  the  bottom  of  a  vast  triassic  deposit  sur- 
rounding Magdeburg."  The  quantity  of  sea  water  which  was 
evaporated  to  produce  saline  deposits  of  more  than  500  meters  in 
thickness  must  have  been  enormous  and  the  rate  of  evaporation 
great.  It  appears  that  a  temperature  of  100°  would  have  been 
quite  necessary,  acting  for  a  long  time,  to  produce  this  result. 

These  authors,  therefore,  admit  that  all  the  theories  so  far  ad- 
vanced to  explain  the  magnitude  of  these  deposits  are  attended 
with  certain  difficulties.  What,  for  instance,  could  have  caused 
a  temperature  of  100°  ?  The  most  reasonable  source  of  this  high 
temperature  must  be  sought  for  in  the  violent  chemical  action 
produced  by  the  double  decompositions  of  such  vast  quantities 
99  Trait^  des  Giles  mineraux,  1893,  1  :  429. 


AGRICULTURAL,  ANALYSIS 

of  salts  of  different  kinds.  There  may  also  have  been  at  the 
bottom  of  this  basin  some  subterranean  heat  such  as  is  found  in 
certain  localities  where  boric  acid  is  deposited. 

Whatever  be  the  explanation  of  the  source  of  the  heat,  it  will 
be  admitted  that  at  the  end  of  the  permian  period  there  was 
thrown  up  to  the  northeast  of  the  present  saline  deposits  a  ridge 
extending  from  Helgoland  to  Westphalia.  This  dam  estab- 
lished throughout  the  whole  of  North  Germany  saline  lagoons 
in  which  evaporation  was  at  once  established,  and  these  lagoons 
were  constantly  fed  from  the  sea. 

There  was  then  deposited  by  evaporation,  first  of  all,  a  layer 
of  gypsum  and  afterwards  rock  salt,  covering  with  few  excep- 
tions the  whole  of  the  area  of  North  Germany. 

But  around  Stassfurt  there  occurred  at  this  time  geologic  dis- 
placements, the  saline  basin  was  permanently  closed  and  then  by 
continued  evaporation  the  more  deliquescent  salts,  such  as  poly- 
halit,  kieserit,  and  carnallit,  were  deposited. 

These  theories  account  with  sufficient  ease  for  the  deposition 
of  the  saline  masses,  but  do  not  explain  why  in  those  days  the 
sea  water  was  so  rich  in  potash  and  why  potash  is  not  found  in 
other  localities  where  vast  quantities  of  gypsum  and  common 
salt  have  been  deposited.  It  may  be  that  the  rocks  composing 
the  shores  of  these  lagoons  were  exceptionally  rich  in  potash 
and  that  this  salt  was,  therefore,  in  a  certain  degree,  a  local 
contribution  to  the  products  of  concentration. 

416.  Sources  of  Supply. — The  Stassfurt  deposits,  which  have  for 
many  years  been  almost  the  sole  source  of  potash  in  fertilizers, 
were  first  known  as  mines  of  rock  salt.  In  1839,  having  pre- 
viously been  acquired  by  the  Prussian  treasury,  they  were  aban- 
doned by  reason  of  the  more  economical  working  of  rock  salt 
quarries  in  other  localities.  It  was  determined  thereafter  to  ex- 
plore the  extent  of  these  mines  by  boring,  and  a  well  was  sunk  to 
the  depth  of  246  meters,  when  the  upper  layer  of  the  salt  deposit 
was  reached.  The  boring  was  continued  into  the  salt  to  a  total 
depth  of  581  meters  without  reaching  the  bottom.  The  results 
of  these  experiments  were  totally  unexpected.  Instead  of  get- 
ting a  brine  saturated  with  common  salt,  one  was  obtained  con- 


MINING    THE    SALTS  489 

taining  large  quantities  of  potassium  and  magnesium  chlorids.1 
Shafts  were  sunk  in  other  places,  and  with  such  favorable  results 
that  in  1862  potash  salts  became  a  regular  article  of  commerce 
from  that  locality.  At  first  these  salts  were  regarded  as  trouble- 
some impurities  in  the  brine  from  which  common  salt  was  to 
be  made,  but  at  this  time  the  common  salt  has  come  to  be  re- 
garded as  the  disturbing  factor.  At  the  present  time  the  entire 
product  is  controlled  by  a  syndicate  of  nine  large  firms  located 
at  Stassfurt  and  vicinity.  Outside  of  the  syndicate  properties 
a  shaft  has  been  sunk  at  Sonderhausen  and  also  at  Anderbeck 
(Halberstadt),  which,  however,  have  produced  only  carnallit. 

It  is  thus  seen  that  the  potash  deposits  extend  over  a  wide  area 
in  Germany,  and  there  is  little  fear  of  the  deposits  becoming  ex- 
hausted in  many  centuries.  In  this  country  no  potash  deposits 
of  any  commercial  importance  have  been  discovered;  but  the 
geological  conditions  requisite  to  these  formations  have  not  been 
wanting,  and  their  future  discovery  is  not  improbable. 

417.  Deposits  of  Potash  Salts  in  Alsace. — Up  to  the  present 
time  it  has  been  supposed  that  the  deposits  of  potash  salts  in 
Germany  were  confined  to  Saxony  and  to  the  Duchy  of  Anhalt.2 
The  investigations  of  recent  years  have  shown  also  that  there  are 
deposits  in  Mecklenburg,  in  the   Duchy  of  Brunswick  and  in 
the  provinces  of  Hanover  and  Oldenburg.     It  has  also  been  re- 
ported recently  that  extensive  deposits  have  been  found  in  Al- 
sace between  the  towns  of  Soultz  and  Regisheim,  on  the  north, 
and  Niedermonchviller  on  the  south.     These  deposits  were  found 
at  the  depths  of  500  and  700  meters,  consisting  of  a  layer  of 
potash  salts  of  superior  quality  one  meter  in  thickness,  and  of 
an  inferior  quality  of  five  meters  in  thickness.     The  crude  salts 
were  found  to  contain  from  20  to  40  per  cent,  of  potassium 
chlorid.     The  total  quantity  of  potash  salts  produced  in   Ger- 
many in  1906  is  estimated  at  5,500,000  tons  and  of  a  value  of 
$20,500,000. 

418.  Mining  the  Salts. — The  potash-bearing  strata,  from  1200 
to  2500  feet  below  the  earth's  surface,  are  reached  by  ordinary 

'  Maercker,  Die  Kalidiingung,  2nd  Edition,  1893  :  i. 
*  The  American  Fertilizer,  1908,  28  :  15. 


49°  AGRICULTURAL  ANALYSIS 

mine  shafts.  In  sinking  these  shafts  great  care  is  taken  to  pre- 
serve unbroken  the  cap  materials  impervious  to  water,  and  thus 
to  prevent  the  highly  soluble  potash-bearing  salts  from  being 
rapidly  leached  or  washed  away.  This  inflow  of  water  is  made 
impossible  by  sinking  iron  tubes  or  lining  the  shafts  with  con- 
crete. Water  is  the  great  danger  in  potash  mining,  and  has 
destroyed  valuable  mines.  Generally,  potash  mines  have  a  re- 
serve or  emergency  shaft,  some  distance  from  the  working  shaft, 
protected  by  strong  safety-pillars.  Another  mining  difficulty  is 
the  "pillaring"  or  supporting  the  mine-roof  as  its  mineral  sup- 
ports are  cut  away.  Formerly  pillars  of  salt  were  left  for  this 
purpose,  but  they  disintegrated  so  rapidly  as  to  be  dangerous, 
and  the  safer  system  was  adopted  of  completely  filling  up  the 
excavations  with  the  waste  salts  and  rock  salt.  Within  the 
mines,  potash  salts  are  broken  down  by  blasting  as  in  ordinary 
mining.  In  many  of  the  works  electricity  is  used  for  motor 
power  and  in  lighting.  The  mines  are  necessarily  kept  perfectly 
dry,  and  visitors  are  free  from  the  inconvenience  and  discom- 
fort usual  to  underground  workings.  The  carnallit  blastings  tear 
off  large  blocks,  which  are  broken  up  by  the  miners  and  trans- 
ported in  small  cars  to  the  shafts,  thence  to  be  hoisted  to  the  sur- 
face and  delivered  to  the  chemical  works  for  grinding  and  fur- 
ther treatment. 

419.  Methods  of  Conducting  the  Mining  Operations. — These  are 
shown   in  the   accompanying   illustrations.     Fig.   40   shows   the 
general  appearance  of  the  interior  of  a  mine,  especially  the  man- 
ner in  which  the  strata  after  deposition  have  been  twisted  and  dis- 
placed by   seismic   disturbances.     In   Fig.   41    is   illustrated   the 
manner  of  drilling  preparatory  to  a  blast,  and  also  the  debris  of 
the  blasting  and  other  mining  operations.     The  tunnels  are  so 
driven  as   to  support  the   superincumbent   mass.     A   noon-day 
luncheon  party  is  shown  in  Fig.  42.     The  illustrations  are  from 
photographs  furnished  by  the  German  Kali  Syndicate. 

420.  Manufacturing  the  Concentrated  Salts. — As  has  been  in- 
timated, at  the  mine  mouths  are  extensive  and  completely  equipped 
chemical  works  which  refine  the  crude  salts  and  separate  their 
constituents  into  products  best  suited^ to  the  various  chemical  in- 


MANUFACTURING    THE    CONCENTRATED    SALTS  4QI  ' 

dustries.3  A  most  important  feature  of  the  refining  is  the  re- 
duction in  weight  by  rejecting  useless  constituents  of  the  salts, 
thus  securing  the  valuable  potash  in  a  small  bulk — an  essential 
consideration  for  the  man  who  pays  the  freight  or  handles  the 
products.  Yet  to  refine  closely  is  an  expensive  process,  and 
much  study  and  great  care  are  necessary  to  balance  properly  the 
amount  of  concentration  against  the  diverse  uses  and  the  cost  of 
shipping  and  handling  the  various  materials.  In  estimating  the 
quantity  of  potash  in  the  different  products,  chemists  are  accus- 
tomed to  make  use  of  the  term  "actual  potash,"  that  is,  potas- 
sium oxid  (K2O).  The  object  of  this  is  to  establish  a  basis  of 
comparison  of  all  potash  salts ;  therefore,  when  "potash"  is  named 
in  potash  products,  it  is  understood  that  the  word  refers  to  the 
amount  of  actual  potash  present,  and  not  the  quantity  of  sulfate 
or  chlorid  of  potash,  as  the  case  may  be.  As  a  matter  of  fact, 
potash  is  not  sold  commonly  in  the  form  of  "actual  potash" 
(K2O),  but  as  sulfate  of  potash,  muriate  (chlorid)  of  potash, 
sulfate  of  potash-magnesia,  etc.  Sulfate  of  potash  is  simply  actual 
potash  combined  with  sulfuric  acid ;  and  muriate  of  potash,  actual 
potash  combined  with  muriatic  (hydrochloric)  acid. 

In  manufacturing  muriate  of  potash  from  the  crude  minerals 
found  in  the  Stassfurt  mines,  all  lime,  soda,  magnesia  and  other 
salts  are  removed.  Crude  carnallit,  as  it  comes  from  the  mines, 
contains  on  an  average  1 5  per  cent,  muriate  of  potash ;  the  manu- 
facturing process  consists  in  separating  this  15  per  cent,  from 
the  85  per  cent,  of  other  crude  ores,  and  makes  use  of  the  chemical 
knowledge  that  these  other  salts  are  either  more  soluble  or  less 
soluble  in  water  and  other  solutions  than  pure  muriate  of  potash. 
The  coarsely  ground  carnallit  is  "charged"  into  a  large  dissolv- 
ing vat  containing  a  boiling,  saturated  solution  of  magnesium 
chlorid  (  a  by-product  of  the  process,  as  shown  below).  The 
mixture  is  agitated  thoroughly  by  means  of  a  "blow-up,"  or  live 
steam  jet,  and  is  boiled  until  it  shows  a  degree  of  concentration 
equal  to  32°  Beaume.  The  contents  are  drawn  off  into 
settling  tanks,  from  which  the  clear  solution  is  run  into  crystal- 
lizing vats  and  left  three  or  four  days  to  cool  and  crystallize, 

3  German  Kali  Works,  The  Stassfurt  Industry,  1902  :  29. 


492  AGRICULTURAL  ANALYSIS 

the  deposit  containing  about  60  per  cent,  pure  muriate  of  potash. 
The  liquors  drawn  from  the  crystallizing  vats  are  boiled  down 
(now  almost  exclusively  in  a  vacuum  apparatus,  but  formerly  in 
open  pans),  during  which  process  some  chlorid  of  sodium  and 
sulfate  of  magnesium  are  separated.  This  second  solution  is 
settled  and  run  into  crystallizing  vats  where  practically  all  the 
potash  separates  as  crystals  of  pure  artificial  mineral  carnallit 
(KC1,  MgCl2,  6H2O),  which  is  treated  precisely  as  was  the  crude 
carnallit  and  gives  a  nearly  pure  muriate  of  potassium  in  one 
crystallization. 

The  crystallized  muriate  of  potash  thus  produced  is  contam- 
inated by  chlorids  of  sodium  and  magnesium,  through  adhering 
solutions,  and  these  impurities  are  removed  by  a  series  of  wash- 
ings with  water.  The  liquor  from  these  washings  of  the  crystals 
is  saved  and  used  on  fresh  batches  of  the  mineral  ore.  The  crys- 
tals of  muriate  of  potash  are  dried  and  are  from  70  to  99  per 
cent,  pure  (KC1).  The  last  "mother  liquors,"  or  solutions  from 
the  crystallizing  vats  (from  which  all  the  potash  has  been  sep- 
arated), are  used  for  the  manufacture  of  bromin  and  chlorid  of 
magnesium. 

The  muriate  of  potash  (chlorid  of  potassium)  manufactured 
at  Stassfurt  is  of  various  grades  and  contains  actual  potash  in 
the  following  proportions : 

Pure  Muriate  of  Potash.  Actual  Potash. 

70  to  75  per  cent,     contains  46.7  per  cent. 

So  to  85  per  cent,     contains  52.7  per  cent. 

90  to  95  per  cent,     contains  57.9  per  cent. 

98  per  cent,     contains  62.0  per  cent. 

When  sold  for  fertilizing  purposes  it  is  on  the  basis  of  80 
per  cent,  pure  muriate  of  potash,  corresponding  to  50.5  per  cent, 
actual  potash.  The  price  is  based  on  this  average  and  is  in- 
creased or  decreased  according  to  the  percentage  above  or  below 
it  of  pure  muriate  contained,  as  shown  by  chemical  analysis. 
Muriate  of  potash  serves  as  a  basis  for  the  manufacture  of  many 
other  potash  salts,  such  as  nitrates,  chlorates,  etc. 

There  are  many  by-products  in  the  manufacture  of  muriate 
of  potash,  notably  magnesium  chlorid  and  sulfate  of  soda,  which 
latter,  owing  to  its  purity  and  freedom  from  acid  salts,  is  largely 


MANUFACTURING    THE    CONCENTRATED    SALTS  493 

used  in  the  manufacture  of  the  cheaper  grades  of  glass.  From 
the  residuum  of  the  first  solution  of  carnallit,  treated  with  cold 
water,  kieserit  (sulfate  of  magnesia)  settles  out  in  fine  crystalline 
particles,  and  is  moulded  into  blocks.  Large  quantities  of  bromin 
and  iron  bromid  are  obtained  at  the  end  of  the  process.  Some 
of  the  Stassfurt  factories  also  prepare  calcined  magnesia,  hydrate 
of  magnesia,  calcium  chlorid,  carbonate  of  potash,  carbonate  of 
potash-magnesia,  etc. 

In  order  to  obtain  the  complete  extraction  of  potash,  the  pro- 
cesses of  manufacture  are  complex,  and  solutions  and  salts  re- 
quire repeated  handling.  It  naturally  follows  that  the  separa- 
tion of  commercially  pure  salts  from  solutions  of  other  salts  is 
an  expensive  process,  and  that  it  is  only  by  the  most  painstaking 
care  and  full  utilization  of  every  possible  by-product  that  potash 
salts  can  be  produced  and  sold  at  the  present  low  prices. 

Sulfate  of  potash  is  manufactured  in  less  quantities  than  muri- 
ate, owing  to  the  smaller  demand  for  it  in  the  market;  but  its 
consumption  is  rapidly  increasing.  There  are  several  processes 
of  manufacture.  The  one  in  general  use  is  to  concentrate  a  solu- 
tion of  kainit  to  a  certain  specific  gravity,  and  then  allow  it  to 
cool  slowly  in  large  crystallizing  vats.  The  resulting  crystals  are 
washed  and  dried,  and  form  the  commercial  salt  sulfate  of  potash- 
magnesia,  containing  generally  40  per  cent,  of  sulfate  of  potash, 
but  when  calcined,  48  per  cent.  In  the  manufacture  of  sulfate 
of  potash  a  solution  of  sulfate  of  potash-magnesia  and  a  given 
quantity  of  muriate  of  potash  are  boiled  together,  whereupon 
the  less  soluble  sulfate  of  potash  separates  and  falls  as  a  precipi- 
tate, after  which  the  solution  is  boiled  down  to  a  certain  specific 
gravity,  and  cooled  slowly  in  crystallizing  vats,  where  the  residual 
potash  separates  as  crystals  of  sulfate  of  potash.  As  it  is  sold, 
it  varies  from  90  to  96  per  cent,  pure,  equivalent  to  46  to  52  per 
cent,  actual  potash. 

The  following  tables  give  the  average  analyses  of  the  more 
important  Stassfurt  potash  salts.  The  figures  show  the  pounds 
of  various  substances  in  100  pounds  of  the  different  salts. 

The  numerous  by-products  obtained  in  refining  the  crude  potash 
salts  are  utilized  in  many  ways  and  for  various  purposes.  Some 


494  AGRICULTURAL  ANALYSIS 

of  them  contain  from  20  to  30  per  cent,  actual  potash,  but  in 
most  cases  in  such  combination  as  not  to  pay  for  the  necessarily 
expensive  extraction.  Because  of  this  comparatively  large  con- 
tent of  potash,  however,  they  are  dried,  calcined,  pulverized,  and 
mixed  with  crude  salts,  or  other  poorer  forms  of  potash,  to  in- 
crease the  potash  content  of  these  salts  and  give  them  added 
value  for  agricultural  purposes. 

Besides  the  agricultural  use  of  potash  salts,  large  quantities 
are  consumed  by  the  chemical  industry  in  Germany,  the  United 
States  and  other  countries,  in  the  manufacture  of  caustic  potash, 
carbonate,  nitrate,  chlorate,  chromate,  bichromate,  alum,  cyanid, 
bromid,  permanganate  and  yellow  prussiate  of  potash  and  of  other 
compounds. 

COMPOSITION  OF  CRUDE  SALTS  (NATURAL  PRODUCTS). 

Kainit.        Carnallit.        Sylvinit. 
Per  cent.       Per  cent.        Per  cent. 

Actual  Potash  (K2O) 12.8  9.8  17.4 

Minimum  Guarantee  (K2O) 12.4  9.0  12.4 

Sulfate  of  Potash  (K2SOJ 21.3            1.5 

Muriate  of  Potash  (KC1) 2.0  15.5  26.3 

Sulfate  of  Magnesia  (MgSOJ 14.5  12.1  2.4 

Chlorid  of  Magnesia  (MgClj) 12.4  21.5  2.6 

Chlorid  of  Sodium  (NaCl) 34-6  22.4  56.7 

Sulfate  of  Lime  (CaSO4)    1.7  1.9  2.8 

Insoluble  Substances 0.8  0.5  3.2 

Water 12.7  26.1  4.5 


SULFATES  (NEARLY  FREE  OF  CHLORIDS). 

Sulfate  of  Potash. 


Sulfate 


90                    96  of  Potash 

per  cent.  per  cent.  Magnesia. 

Actual  Potash  (K,O) 49-9  52-7  27.2 

Minimum  Guarantee  (K,O) 48.6  51.8  25.9 

Sulfateof  Potash  (K,SO<) 90.6  97.2  50.4 

Muriate  of  Potash  (KC1) 1.6  0.3 

Sulfate  of  Magnesia  (MgSO4) 2.7  0.7  34.0 

Chlorid  of  Magnesia  (MgCl,) i.o  0.4 

Chlorid  of  Sodium  (NaCl) 1.2              0.2  2.5 

Sulfate  of  Lime  (CaSO4) 0.4              0.3  0.9 

Insoluble  Substances 0.3              0.2  0.6 

Water 2.2              0.7  n.6 


KAINIT 


COMPOSITION  OF  SALTS  CONTAINING  CHIX>RIDS. 


495 


Potash  Manure  Salts. 


.  »  1  U 

litllC     U  1      i    Ul. 

aau. 

'  .     . 

M'     '            ' 

90/95 
per  cent. 

C7  O 

80/85 
per  cent. 

r-5  n 

70/75 

per  cent. 

Aft   *7 

20 

per  cent. 

^  T  n 

3° 
percent. 

^rt  fi 

Minimum  Guarantee 
Sulfate  of  Potash 

0/-9 
56.8 

Oz-7 
50.5 

40.7 
44.1 

T    1 

•  A»W 

20.0 
2.O 

yj.  o 
30.0 
1.2 

Muriate  of  Potash  .  . 

91.7 

83.5 

••/ 

72-5 

31-6 

47-6 

Sulfate  of  Magnesia 

O.2 

0.4 

0.8 

10.6 

9-4 

Chlorid  of  Magnesia 

0.2 

°-3 

0.6 

5-3 

4.8 

Chlorid  of  Sodium  .  . 

7-1 

14-5 

21.2 
O.  2 

40.2 

2.1 

26.2 

2.2 

Insoluble  Substances 
Water.. 

O.2 
0.6 

0.2 
I.  T 

0.5 

2.K 

4.0 
X.2 

3-5 
«:.T 

421.  Detailed  Description  of  the  Principal  Salts  Used  in  the 
Manufacture  of  Fertilizers. — Some  of  the  salts  of  potash  such  as 
kainit,  are  used  as  fertilizers  just  as  they  are  taken  from  the  mine. 
Others,  such  as  carnallit  and  sylvinit,  may  be  used  directly  as  fer- 
tilizer, but  more  commonly  are  subjected  to  a  process  of  manu- 
facture or  concentration  whereby  other  compounds  are  produced. 
A  description  of  the  more  important  salts  follows. 

422.  Kainit. — The  most  important  of  the  natural  salts  of  potash 
for  fertilizing  purposes  is  the  mixture  known  as  kainit.     It  is 
composed  in  a  pure  state  of  a  molecule  each  of  potassium,  sul- 
fate,  magnesium  sulfate,  magnesium  chlorid,  and  water.     Chem- 
ically it  is  represented  by  the  symbols : 

K2SO4.MgSO4.MgCl2.H2O.  Its  theoretical  percentage  of  pot- 
ash (K2O),  oxygen— 1 6,  is  23.2. 

Pure  kainit,  however,  is  never  found  in  commerce.  It  is  mixed 
naturally  as  it  comes  from  the  mines  with  common  salt,  potassium 
chlorid,  gypsum,  and  other  bodies.  The  content  of  potash  in  the 
commercial  salt  is,  therefore,  only  a  little  more  than  half  that  of 
the  pure  mineral.  In  general  it  may  be  taken  at  12.5  per  cent., 
of  which  more  than  one  per  cent,  is  derived  from  the  potassium 
chlorid  present.  The  following  analysis  given  by  Maercker  may 
be  regarded  as  typical:4 

4  Die  Kalidiingung,  2nd  Edition,  1893  :  5. 


AGRICULTURAL  ANALYSIS 

Per  cent. 

Potassium  sulfale 21.3 

»  J 

Magnesium  sulfate 14.5 

Magnesium  chlorid 12.4 

Potassium  chlorid , 2.0 

Sodium  chlorid 34.6 

Calcium  sulfate  (gypsum)  1.7 

Water 12.7 

Alumina 0.8 

Kainit  occurs  as  a  crystalline,  partly  colorless,  partly  yellow- 
red  mass.  When  ground,  in  which  state  it  is  sent  into  com- 
merce, it  forms  a  fine,  gray-colored  mass  containing  many  small 
yellow  and  red  fragments.  It  is  not  hygroscopic,  and  if  it  be- 
comes moist  it  is  due  to  the  excess  of  common  salt  which  it  con- 
tains. 

According  to  Maercker,  kainit  was  formerly  regarded  as  a 
potassium  magnesium  sulfate.  But  this  conception  does  not  even 
apply  to  the  pure  salt,  much  less  to  that  which  comes  from  the 
mines.  If,  therefore,  the  agronomist  desires  a  fertilizer  free  from 
chlorin  he  would  be  deceived  in  choosing  kainit,  which  may 
sometimes  contain  nearly  50  per  cent,  of  its  weight  of  chlorids. 
Where  a  fertilizer  free  of  chlorin  is  desired,  as,  for  instance,  in 
the  culture  of  tobacco,  kainit  cannot  be  considered.  In  many 
other  cases,  however,  the  chlorin  content  of  this  body,  instead  of 
being  a  detriment,  may  prove  positively  advantageous,  the  chlo- 
rids, on  account  of  their  easy  diffusibility  through  the  soil,  serving 
to  distribute  the  other  ingredients. 

Kainit  is  regarded  in  some  localities  as  a  check  against  the 
ravages  of  insects  and  as  a  preventative  of  cotton  blight. 

By  reason  of  the  presence  of  common  salt  and  magnesium 
chlorid,  the  ground  kainit  delivered  to  commerce  tends  to  harden 
into  compact  masses.  To  prevent  this,  in  Germany  it  is  recom- 
mended to  mix  it  with  about  two  and  a  half  per  cent,  of  fine- 
ly ground,  dry  peat. 

Such  a  mixture  is  recommended  in  all  cases  where  the  freshly 
ground  kainit  is  not  to  be  immediately  applied  to  the  soil. 

The  greater  part  of  the  crude  kainit  mined  is  sold  directly  as 
a  fertilizer,  but  a  part  is  used  also  in  the  manufacture  of  high 
grade  sulfate. 


CARNALUT  497 

In  some  of  the  recently  opened  mines  a  mixture  of  sylvin, 
kieserit  and  rock  salt  is  formed,  known  as  Hartsalz.  This  mix- 
ture contains  almost  the  same  percentage  of  potash  as  kainit.5 

423.  Carnallit. — This  mineral  is  a  mixture  of  even  molecules 
of  potassium  and  magnesium  chlorids  crystallized  with  six  mole- 
cules of  water.  It  is  represented  by  the  symbols  KCl.MgCl2.6H2O. 
As  it  comes  from  the  mines  it  contains  small  quantities  of  potas- 
sium and  magnesium  sulfates  and  small  quantities  of  other  acci- 
dental impurities.  Existing,  as  it  does,  in 'immense  quantities  in 
strata  averaging  more  than  85  feet  in  thickness,  it  has  been  ex- 
tensively used  for  the  manufacture  of  the  commercial  potassium 
chlorid  (muriate  of  potash).  As  mined  its  color  varies  through 
white,  red,  yellow  and  gray.  In  the  strong  light  of  the  electric 
lamp  the  brilliancy  of  carnallit  crystals  and  their  varied  colorings 
produce  a  strikingly  beautiful  effect  in  the  galleries  of  the  mines. 
For  many  purposes  in  agriculture,  for  instance,  fertilizing  to- 
bacco fields,  it  is  not  suited,  and  it  is  less  widely  used  as  a  fer- 
tilizer in  general  than  its  alteration  product,  kainit.  Its  direct 
use  as  a  fertilizer,  however,  is  rapidly  increasing  since  later  ex- 
perience has  shown  that  chlorin  compounds  are  capable  of  a  far 
wider  application  in  agriculture  without  danger  of  injury  than  was 
formerly  supposed.  As  it  comes  from  the  mines,  the  Stassfurt 
carnallit  has  the  following  composition :° 

Per  cent. 

Potassium  chlorid 15.5 

Magnesium  chlorid 21.5 

Magnesium  sulfate 12. 1 

Sodium  chlorid 22.4 

Calcium  sulfate 1  -o 

Water 26.1 

Undetermined 0.5 

Pure  carnallit  would  have  the  following  composition: 

Per  cent. 

Chlorin 38-3 

Potassium 14-0 

Magnesium 8.7 

Water 39-° 

5  German  Kali  Works,  The  Slassfurt  Industry,  1902  :  12. 

6  Maercker.Die  Kalidiingung,  2nd  Edition,  1893  :  7. 


49^  AGRICULTURAL  ANALYSIS 

Equivalent  to 

Per  cent. 

Potassium  chlorid 26.8 

Magnesium  chlorid     34.2 

Water 39.0 

The  commercial  article  as  taken  from  the  mines,  as  is  seen 
above,  has  less  potash  (K2O)  than  kainit,  the  mean  content  being 
about  nine  per  cent.  Those  proposing  to  use  this  body  for  fer- 
tilizing purposes  should  bear  in  mind  that  it  contains  less  potash 
and  more  chlorin  than  kainit. 

Carnallit  occurs  in  characteristic  brown-red  masses.  On  ac- 
count of  its  highly  hygroscopic  nature  it  should  be  kept  as  much 
as  possible  out  of  contact  with  moist  air  and  should  not  be  ground 
until  immediately  before  using. 

By  reason  of  the  greater  bulk  in  proportion  to  its  content  of 
potash  and  its  hygroscopic  nature  and  consequent  increased  dif- 
ficulty in  handling,  the  cost  per  unit  of  potash  in  carnallit  is 
greater  than  in  kainit. 

In  some  localities  small  quantities  of  ammonium  chlorid  have 
been  found  with  carnallit,  but  not  to  exceed  one-tenth  per  cent. 
It  has,  therefore,  no  practical  significance  to  the  farmer,  but  may 
be  of  interest  to  the  analyst. 

424.  Polyhalit. — Polyhalit  is  a  mineral  occurring  in  the  Stass- 
furt  deposits  consisting  of  a  mixture  of  potassium,  magnesium, 
and  calcium  sulfates,  with  a  small  proportion  of  crystal  water. 
This  mineral,  on  account  of  its  being  practically  free  of  chlorin, 
is  one  especially  desirable  for  use  in  those  cases,  as  in  the  culture 
of  tobacco,  where  chlorids  are  injurious.  Unfortunately,  it  does 
not  occur  in  sufficient  quantities  to  warrant  the  expectation  of 
its  ever  being  found  in  masses  large  enough  to  become  a  gen- 
eral article  of  commerce.  It  is  found  only  in  pockets  or  seams 
among  the  other  Stassfurt  deposits,  and  there  is  no  assurance 
given  on  finding  one  of  these  deposits  of  polyhalit  that  it  will 
extend  to  any  great  distance.  The  composition  of  the  mineral 
is  shown  by  the  following  formula:  K2SO4.MgSO4.(CaSO4)2. 
H2O.  Its  percentage  composition  is  shown  by  the  following  num- 
bers: 


SYLVIN  IT  499 

Per  cent. 

Potassium  sulfate 28.90 

Magnesium  sulfate 19-93 

Calcium  sulfate 45- 18 

Water 5.99 

The  percentage  of  potash  corresponding  to  the  above  formula 
is  15.62.  It,  therefore,  contains  a  considerable  excess  of  potash 
over  kainit,  and  on  account  of  its  freedom  from  chlorids  is  pre- 
ferred for  many  purposes. 

425.  Krugit. — This  mineral   occurs   associated  with   polyhalit 
and  differs  from  it  only  in  containing  four  molecules  of  calcium 
sulfate  instead  of  two.  Its  formula  is:   K,SO4.MgSO4.(CaSO4)4. 
H2O.    As  it  comes  from  the  mines  it  is  frequently  mixed  with  a 
little  common  salt.    Its  mean  percentage  composition  as  it  comes 
from  the  mines  is  given  in  the  following  numbers : 

Per  cent. 

Potassium  sulfate 18.60 

Magnesium  sulfate 14. 70 

Calcium  sulfate 61 .00 

Sodium  chlorid i  .50 

Water 4.20 

The  percentage  of  potash  corresponding  to  the  above  formula 
is  10.05.  It  is,  therefore,  less  valuable  than  kainit  in  so  far  as  its 
content  of  potash  is  concerned.  This  salt  also  exists  in  limited 
quantities  and  is  not  likely  to  become  an  important  article  of 
commerce. 

426.  Sylvin. — One  of  the  alteration  products  of  carnallit  is  a 
practically  pure  potassium  chlorid,  which  as  it  occurs  in  the  Stass- 
furt  mines  is  known  as  sylvin.     The  alteration  of  the  carnallit 
arises   from  its  solution   in  water,   from   which,   on   subsequent 
evaporation,  the  potassium  chlorid  is  deposited  alone.    This  min- 
eral is  found  in  only  limited  quantities  in  the  Stassfurt  deposits, 
and  it  therefore  does  not  have  any  great  commercial  importance. 

427.  Sylvinit. — This  mineral  has  been  mined  in  recent  years 
in  considerable  quantities.     It  is,  in  fact,  only  common  salt  car- 
rying large  quantities  of  potassium  chlorid  together  with  certain 
other  accidental  impurities.     It  was  probably  formed  by  the  dry- 
ing up  of  a  saline  mass  in  such  a  way  as  not  to  permit  the  com- 
plete separation  of  its  mineral  constituents.     The  average  com- 


5OO  AGRICULTURAL,  ANALYSIS 

position  of  sylvinit  as  it  comes  from  the  mines  is  given  in  the 
following  table: 

Per  cent. 

Potassium  chlorid 30.55 

Sodium  chlorid 46.05 

Potassium  sulfate 6.95 

Magnesium  sulfate 4.80 

Magnesium  chlorid 2.54 

Calcium  sulfate i  .80 

Water  and  insoluble 7.29 

This  salt  is  richer  in  chlorin  than  any  other  of  the  Stassfurt 
potash  minerals,  containing  altogether  79.14  per  cent,  of  chlo- 
rids.  Its  potash  content  amounts  to  23.04  per  cent.,  but  in  pro- 
portion to  the  potash  which  it  contains,  it  is  relatively  poorer  in 
chlorin  than  kainit  and  carnallit.  On  account  of  its  high  con- 
tent of  potash  the  cost  of  a  unit  thereof  as  contained  in  sylvinit 
is  less  than  in  kainit  and  carnallit. 

428.  Kieserit. — The  mineral  kieserit  is  essentially  magnesium 
sulfate     and   it  does  not  necessarily   contain  any  potash   salts. 
Under  the  name  of  kieserit,  however,  or  bergkieserit,  there  is 
mined  a  mixture  of  carnallit  and  kieserit,  which  is  a  commercial 
source  of  potash.     The  mixture  contains  the  following  average 
content  of  the  bodies  named : 

Per  cent. 

Potassium  chlorid 11.80 

Magnesium  sulfate 2 1 . 50 

Magnesium  chlorid 17.20 

Sodium  chlorid 26. 70 

Calcium  sulfate 0.80 

Water •  20.70 

Insoluble 1.30 

This  mixture  contains  only  about  seven  per  cent,  of  potash 
and  would  not  prove  profitable  when  used  at  a  distance  from 
the  mines  on  account  of  the  cost  of  freight.  It  has  proved  val- 
uable, however,  for  a  top  dressing  for  meadow  lands  in  the 
vicinity  of  Stassfurt. 

429.  Schonit. — Among  the  Stassfurt  deposits  there  occurs  in 
small  quantities  a  mineral,  schonit,  which  is  composed  of  the  sul- 
fates  of  potassium  and  magnesium.    The  quantity  of  the  mineral 


POTASSIUM   SULFATE  5OI 

occurring  naturally  is  very  small,  and,  therefore,  it  has  no  com- 
mercial importance.  When,  however,  kainit  is  washed  with  water 
the  common  salt  and  magnesium  chlorid  which  it  contains  being 
more  soluble,  are  the  first  leached  out,  and  the  residue  has  ap- 
proximately the  composition  of  the  pure  mineral.  This  mixture, 
as  prepared  in  the  way  mentioned  above,  has  the  following  aver- 
age composition: 

Per  cent. 

Potassium  sulfate 50.40 

Magnesium  sulfate 34.00 

Sodium  chlorid 2.50 

Water 11.60 

The  percentage  of  potash  corresponding  to  the  above  compo- 
sition is  27.2.  This  substance  being  so  rich  in  potash,  and  prac- 
tically free  of  chlorids,  is  well  suited  to  transportation  to  great 
distances  and  for  general  use  in  the  field.  Since,  however,  a 
considerable  expense  attends  the  manufacture  of  the  artificial 
schonit,  the  advantages  above  named  give  it  very  little,  if  any, 
advantage  in  competition  with  the  other  potash  salts,  as  they 
come  from  the  mines.  It  has,  however,  an  especial  value  for  the 
fertilization  of  tobacco  and  vines. 

430.  Potassium  Sulfate. — Several  grades  of  potassium  sulfate 
are  found  in  the  market  for  fertilizing  purposes,  some  of  them 
quite  pure,  containing  over  97  per  cent,  of  the  pure  sulfate.  The 
following  data  show  the  composition  of  a  high  grade  and  low 
grade  potassium  sulfate  of  commerce : 

High  grade.     Low  grade. 
Per  cent.  Per  cent. 

Potassium  sulfate 97-2O  90.60 

Potassium  chlorid 0.30  1.60 

Magnesium  sulfate 0.70  2.70 

Magnesium  chlorid 0.40  1 .00 

Sodium  chlorid 0.20  1.20 

Insoluble 0.20  0.30 

Water 0.70  2.20 

Naturally,  high  grade  sulfates  of  this  kind  can  only  be  pre- 
pared in  chemical  factories  built  especially  for  the  work.  The 
result  is  that  the  potash  per  unit  is  raised  greatly  in  price.  When, 
however,  the  fertilizers  are  to  be  transported  to  a  great  distance, 


5O2  AGRICULTURAL   ANALYSIS 

the  saving  in  freight  often  more  than  compensates  for  the  higher 
price  of  the  potash.  It  therefore  happens  that  there  are  many 
places  in  this  country  where  the  actual  price  of  potash  per  pound 
is  less  in  high  grade  sulfates  than  in  kainit  or  carnallit.  When, 
in  addition  to  this,  the  especial  fitness  of  the  high  grade  sulfates 
for  certain  kinds  of  fertilization,  especially  tobacco  growing,  is 
considered,  it  is  seen  that  at  this  distance  from  the  mines  these 
high  grade  salts  are  of  no  inconsiderable  importance.  The  per- 
centage of  potash  in  the  high  grade  sulfates  often  exceeds  50. 

431.  Potassium-Magnesium  Carbonate. — This    salt    has    lately 
been  manufactured  and  used  to  a  considerable  extent,  especially 
for  tobacco  fertilizing.     As  furnished  to  the  trade  it  has  the  fol- 
lowing average  composition : 

Per  cent. 

Potassium  carbonate 35  to  40 

Magnesium  carbonate 33  to  36 

Water  of  crystallization 25 

Potassium  chlorid,  potassium  sulfate,  and  insoluble- •       2  to    3 

The  content  of  potash,  as  is  seen  from  the  above  formula, 
amounts  to  from  20  to  25  per  cent.  The  compound  is  completely 
dry,  is  not  hygroscopic,  and  is,  therefore,  always  ready  for  distribu- 
tion. It  is  especially  to  be  recommended  for  all  those  intensive 
cultures  where  it  is  feared  that  chlorids  and  sulfates  will  prove 
injurious,  especially  in  the  cultivation  of  tobacco. 

432.  Potash  in  Factory  Residues. — The  residues  from  the  potash 
factories  in  Stassfurt  and  vicinity  contain  considerable  quantities 
of  potash  and  attempts  have  been  made  to  recover  this  waste  and 
put  it  into  form  for  fertilizing  uses.     The  waste  waters  of  the 
factories  are  sometimes  collected  and  evaporated,  and  the  residue 
incinerated.     The  content  of  potash  in  these  residues  is  extremely 
variable,  usually  quite  low,  and  they,  therefore,  can  not  be  recom- 
mended for  fertilizing  purposes,  especially  if  they  are  to  be  trans- 
ported to  any  distance. 

433.  Production  of  Crude  Salts. — The     following    table    gives 
the  production  of  crude  salts,  in  the  Stassfurt  region  from  1888 
to  the  close  of  1901 : 


PRODUCTION    OF    CONCENTRATED    POTASH    SALTS 


503 


Rock 

Year 

Carnallit 

kieserit 

1888 

849,603 

10,754 

1889 

798,721 

9,354 

1890 

838,526 

6,951 

1891 

818,862 

5,816 

1892 

736,751 

5,783 

1893 

794,660 

4,807 

1894 

851,339 

3,865 

1895 

782,944 

3,012 

1896 

856,223 

2,841 

1897 

851,272 

2,619 

1898 

990,998 

2,444 

1899 

1,317,948 

2,066 

1900 

1,697,803 

2,047 

1901 

1,860,189 

2,335 

Kainit  and 

hartsalz 

Total 

375,574 

1,238,151 

362,611 

1,199,015 

401,871 

1,279,265 

512,794 

1,369,833 

585,775 

1,360,978 

689,994 

1,538,601 

729,301 

1,648,000 

669,532 

1,531,585 

833,025 

1,782,479 

1,012,186 

1,950,182 

I,I20,6l6 

2,208,328 

1,063,195 

2,483,862 

1,189,394 

3,037,035 

1,432,136 

3,484,694 

(METRIC  TONS  OF  2204  POUNDS.) 

Sylvinit 
2,220 
28,329 

3I.9I7 
32,66l 
32,669 
49,140 

63.495 
76,097 
90,390 
84.105 
94,270 
100,653 

147,791 
190,034 

Carnallit  leads  in  the  total  quantity  mined,  followed  closely  by 
kainit  and  hartsalz.  The  relative  quantity  of  carnallit,  however, 
is  decreasing,  while  that  of  kainit  and  sylvinit  is  increasing. 

These  salts  were  either  sold  directly  from  the  mines  for  agricul- 
tural purposes,  or  manufactured  into  more  concentrated  potash 
products  for  use  in  agriculture,  or  in  the  arts  and  other  manu- 
factures. The  greater  part  of  the  crude  salts  manufactured  into 
concentrated  products  was  converted  into  muriate  of  potash. 

434.  Production  of  Concentrated  Potash  Salts. — The  following 
table  gives  full  detailed  data  as  to  the  various  concentrated  salts 
produced  from  1884  to  the  close  of  1901 : 

(METRIC  TONS  OF  2204  POUNDS). 

Sulfate  of 


. 

Sulfate  of 

potash-magnesia 

Potash 

Kieserit 
Kieserit      jjround 

potash,  80 

potash,  90 

Crystallized,   Calcined 

manure 

in              and 

Year 

per  cent. 

per  cent. 

40  per  cent 

48  per  cent.        salt 

blocks      calcined 

1884 

106,330 

3.000 

400 

8,000 

9,500 

17,800 

1885 

104,500 

4,000 

450 

9,OOO 

8,400 

l8,500 

1886 

IIO.2OO 

3.639 

472 

10,111 

8,161 

19,500 

1887 

130,000 

10,528 

500 

6,285 

8,163 

24,018 

1888 

132,000 

10,916 

522 

11,380 

13-918 

28,325 

1889 

I31,  593 

7,321 

67I 

9,215 

17,285 

31,824 

1890 

134,760 

13,839 

907 

10,830 

17,620 

32,005 

1891 

143,488 

18,981 

1,053 

II,4OO 

16,045 

28,559 

1892 

121,028 

15,466 

708 

11,842 

16.895 

23,855                 II 

1893 

132,529 

16,361 

739 

",643 

17,344 

24,386               105 

1894 

147,936 

15,243 

1,780 

I2JI8 

19,728 

26,440            216 

1895 

145,027 

13.403 

898 

8,249 

19,724 

25,115        142 

1896 

155-805 

13,889 

1,051 

4,622 

19,253 

24,987               211 

1897 

158,863 

15,403 

922 

7,415 

23,042 

25,669               214 

1898 

I74,38o 

17,781 

914 

io,535 

24,284 

19.934               728 

1899 

180,672 

24,656 

579 

8,459 

70,916 

28,2l6               260 

1900 

206,471 

31,255 

932 

12,150 

129.863 

28,508               358 

1901 

211,421 

28,196 

936 

",750 

147,170 

26,727               361 

504  AGRICULTURAL  ANALYSIS 

435.  Consumption  of  Potash  for  Agricultural  Purposes  in  Dif- 
ferent Countries. — The  following  tables  show  the  consumption 
of  potash  for  agricultural  purposes  in  the  principal  countries  of 
the  world  for  six  years,  and  the  relative  quantity  used  per  acre 
of  land  under  cultivation  : 

(a)  TOTAL  CONSUMPTION  IN  TONS  CALCULATED  IN  PURE  POTASH  (K2O). 

Country   .        1895       1896       1897       1898      1899  1900 

Germany 60,182        75,585        89,683        96,414       107,688       117,712 

United  States ...     33,907        38,018        46,628        51,663        50,855  66,595 

France 5,033          5,892          7,266          6,532          8,772  8,229 

Sweden 5,061          5,719          6,869          7,637          6,892  8,197 

Holland 2,542          2,964          4,091          5,032          6,021  7,106 

England -|              ~\                         3,165          3,871          4,014  4,020 

Scotland j-  4,088  I      4,569           1,487          1,782          2,584  3,370 

Ireland •  .  J                                            297             285             412  600 

Belgium 2,881           2,681          2,829          3,  no          3,367  3,607 

Austria-Hungary       1,045          1,196          i,349          1,630          2,256  2,389 

Spain 369             456             770          1,128          1,953  2,428 

Denmark 834           1,071           1,030          1,375          1,320  1,692 

Russia 467             620             625          i,on           1,037  1,597 

Italy 883             792             938          1,235          1,197  1,380 

Switzerland 833             876             953             931           1,038  1,026 

Finland 181             332          §  466             566             505  382 

Norway 69             107             164             252             238  286 

Portugal 68               46               44             119               13  43 

(6)    CONSUMPTION  OF  PURE  POTASH  (K,O)  CALCULATED  IN 
POUNDS  PER  loo  ACRES  ARABLE  LAND. 

Arable  land 

Country                          in  acres              1895           1896           1897           1898           1899  1900 

Germany 86,971,300       152.5       191.6      227.3       244.3      273.0     298.3 

Holland 5,012,100       111.7       J3°-3       J79-9      212.3      264.7  312.5 

Sweden 8,622,000      129.3       146.2       175.5       I95-2      176.2  209.5 

Scotland 3,641,200        77.3        86.3        90.0       107.8      156.5  204.0 

Belgium 5,232,800      121.3       112.9      119.2       131.0      141.8  151.9 

Denmark 6,305,000        29.2        37.5        36.0        48.1        46.1  59.1 

England 16,915,400        33.3        37.2        41.2        50.4        52.3  52.4 

Norway 1,412,900         10.7         16.7         25.7         39.3        37.1  44.7 

Switzerland 5,258,700        35.0        36.8        40.0        39.0       43.5  43.0 

United  States ...  348,212,300        21.5        24.1         29.5        32.7        32.2  42.2 

Finland 2,755,100        14.5        26.3        37.3        45.3       40.4  30.6 

Ireland 5,322,500        10.6        11.9        12.3         n.8        17.0  24.8 

France 92,649,800        12.0        14.0        17.3        15.5        20.9  19.5 

Spain 72,201,100          1.2          1.4          2.3          3.5         6.0  7.4 

Italy 50,421,000          3.8          3.5          4.1           5.4         5.3  6.1 

Austria-Hungary    99,416,900          2.3          2.7          3.0          3.7         50  5.3 

Portugal 11,329,000          1.3          0.9          0.9          2.3         0.3  0.8 

Russia 515,055,200          0.2       '  0.3          0.3          0.4         0.4  0.7 


ACTUAL   POTASH    USED    IN   DIFFERENT    STATES 


505 


It  is  seen  that  Germany  is  the  greatest  consumer  of  these  salts, 
and  the  United  States  the  next  in  actual  quantity  used.  Other 
countries  use  comparatively  small  quantities,  but  some  of  them  use 
larger  quantities  per  acre  of  land  under  cultivation  than  are  used 
in  this  country. 

436.  Amount  of  Actual  Potash  Used  in  Different  States. — The 
relative  quantities  of  potash  used  in  the  different  states  are  shown 
in  the  following  table : 

DATE  OF  COMPILATION,  JULY  8,  1901. 

Tons  actual  potash  sold  in  the 
various  states  in  1899,  as  per 


State 


NORTH 

Connecticut 

Delaware 

Illinois 

Indiana 

Maine 

Massachusetts  •  • 

Michigan 

Missouri 

New  Hampshire 

New  Jersey 

New  York 

Ohio 200,000 

Pennsylvania...       125,000 
Rhode  Island ...          5,000 

Vermont 13,000 

Wisconsin 2co 

Canada 4,000 


Tons  of 

total 
fertilizer 
consumed 

in  1900 

22,500 
6,OOO 

25,000 

75,000 
6,000 

30,000 
7,000 
7,000 
5,000 

42,929 
125,000 


Total 698,629 


SOUTH 

Alabama 

Arkansas 

Florida 

Georgia 

Kentucky 

Louisiana 

Maryland 

Mississippi 

North  Carolina 
South  Carolina 

Tennessee 

Texas 

Virginia 

West  Virginia  . 


155,746 

1,200 
4O,000 

412,755 
32,6OO 
25,OOO 
85,000 
66,667 

275,000 

250,000 

25,000 

3,900 

200,000 
25,000 


Per 
cent. 

K20 
(Esti- 
mated) 

5-0 

4.0 

I.O 

3-o 
5-o 
2.6 
o.S 
3-0 
6.0 
4.0 

2.0 

3-0 
4.0 
5-0 

2.O 

3-o 


1-5 
i-5 
8.0 

2.O 

3-o 

0.8 
3-8 


2.O 
I.O 
2.0 
2-5 


agent's  statement 


Total 1,597,868 

Grand  total.    2,296,497 


Tons 

KoO 

1,125 

240 

250 

1,125 

180 
1,500 

182 
35 

150 
2,576 
5,000 
4,000 
3,750 

200 

650 
4 

120 

2I,o87 

2,336 

18 
3,200 

8,255 
978 

200 
2,550 
I.OOO 
4,125 
3,750 

500 

39 
4,000 

625 
31,576 
52,663 


For 
agricul- 
tural 
purposes 

565 
118 

659 

Chemical 
purposes 

14 
224 

Total 
579 
'      342 
659 

47 
106 

.... 

47 
1  06 

3,099 

275 

3,374 

252 

252 

20 

M 

34 

1,245 
8,096 
1,026 

3 
3,36o 

1,248 
",456 
1,026 

4,?  84 

200 

4,584 

140 

140 

86 

.... 

86 

19.843 

4,090 

23,933 

724 

.... 

724 

821 

.... 

'821 

4.895 

.... 

4,895 

79 

398 
6,968 

952 

79 
398 
7,920 

449 
2,986 
10,381 
587 

.... 

449 
2,986 
10,381 
587 

4,535 

4,535 

i 

I 

32-824 

952 
5,042 

33,776 
57.7C9 

52,667 

506  AGRICULTURAL,  ANALYSIS 

The  southern  states,  it  is  seen,  use  more  than  twice  as  much 
potash  as  the  northern,  and  this  is  due  chiefly  to  the  application 
of  this  plant  food  to  the  cotton  and  sugar  cane  crops. 

437.  Changes  in  Potash  Salts  in  Situ. — The  deposits  of  potash 
salts     are     not     all    found  at  the  present  in  the  same  condi- 
tion in  which  they  were  first  deposited  from  the  natural  brines. 
The  layers  of  salt  have  been  subjected  to  the  usual  upheavals 
and  subsidences  peculiar  to  geological  history.     The   layers  of 
salt  were  thus  tilted  and  the  edges  often  brought  to  the  surface. 
Here  they  were  exposed  to  solution,   and  the  dissolved  brine 
afterwards  separated  its  crystallizable  salts  in  new  combinations. 
For  instance,  kieserit  and  the  potassium  chlorid  of  the  carnallit 
were  first  dissolved  and  there  was  left  a  salt  compound  chiefly  of 
potassium  and  sodium  chlorids  sylvinit.  In  some  cases  there  was  a 
mutual  reaction  between  the  magnesium  sulfate  and  the  potassium 
chlorid  and  the  magnesium  potassium  sulfate,  schonit,  was  thus 
produced.     This  salt  is  also  prepared  at  the  mines  artificially. 
The  most  important  of  these  secondary  products  however,  from 
the   agricultural   standpoint,   is   kainit.     This   salt   arose  by   the 
bringing  together  of  potassium  sulfate,  magnesium  sulfate,  and 
magnesium  chlorid,  and  was  formed  everywhere  about  the  borders 
of  the  layers  of  carnallit  wherever  water  could  work  upon  them. 
In  quantity  the  kainit,  as  might  be  supposed,  is  far  less  than  the 
carnallit,  the  latter  existing  in  immense  deposits.     There  is,  how- 
ever, quite  enough  of  it  to  satisfy  all  the  demands  of  agriculture 
for  an  indefinite  time.     In  fact  for  many  purposes  the  carnallit 
can  take  the  place  of  kainit  without  detriment  to  the  growing 
crops.     The   relative   positions   and  quantities   of  the  layers   of 
mineral  matters  in  the  potash  mines,  and  the  depth  in  meters  at 
which  they  are  found  is  shown  in  Fig.  43. 7 

438.  Theory  of  Deposition  of  Potash   Salts. — The   conditions 
which  obtained  in  the  evolution  of  the  earth's  crust  upon  which 
the  deposition  of  soluble  salts  depends,  are  of  great  interest  to  ag- 
riculture in  so  far  as  the  laying  down  of  the  stores  of  phosphoric 
acid,  nitrates  and  potash  are  concerned.     Deposits  of  phosphoric 

Maercker,  Die  Kalidiingung,  2nd  Edition,  1893  :  3. 


THEORY   OF  DEPOSITION   OF   POTASH    SALTS 


507 


acid  which  are  stored  are  mostly  insoluble  or  difficultly  soluble 
in  water.     On  the  other  hand,  the  nitrates  which  are  deposited  are 


Fig.  43.     Geological  Relations  of  the  Potash  Deposits  near  Stassfurt. 

very  soluble  in  water  and  this  is  true,  though  to  a  less  extent, 
with  potash  compounds.     Nevertheless,  all  of  these  potash  depos- 


508  AGRICULTURAL  ANALYSIS 

its  have  been  deposited  according  to  the  conditions  of  concentra- 
tion and  temperature  to  which  the  original  solutions  have  been 
subjected.  The  laws  which  govern  the  cooling,  concentration  and 
deposition  of  chemical  compounds  in  different  degrees  of  solu- 
bility are  now  well  known.  The  theories  of  solution  have  been 
fully  expounded  and  verified  by  actual  demonstration. 

It  is  evident  that  the  depositions  of  potash  salts  must  have  come 
from  the  gradual  concentration  or  cooling,  or  both,  of  the  original 
solution.  It  is  further  evident  that  these  original  solutions  were 
secured  by  the  action  of  fresh  or  salt  water  upon  rock  deposits 
rich  in  potash.  In  going  into  solution  the  potash  salts,  in  re- 
sponse to  the  law  of  equilibrium,  have  combined  with  different 
acids,  producing  salts  of  different  degrees  of  solubility.  The 
salts  of  the  same  solubility,  obeying  a  well-known  law,  tend  to 
be  precipitated  in  certain  given  conditions  of  concentration  and 
temperature.  Thus,  nature  separates  sometimes  completely  and 
sometimes  incompletely,  not  only  the  similar  salts  of  potash,  but 
also  other  saline  compounds  whose  deposition  depends  upon  sim- 
ilar conditions.  By  the  combined  action  of  these  forces  the  vast 
potash  deposits  which  are  found  in  different  parts  of  the  world 
but  especially  near  Stassfurt,  in  Germany,  have  been  produced. 

It  is  well  known  that  almost  all  chemical  substances  which  exist 
in  rocks,  as  incidental  or  principal  constituents  thereof  are  found 
in  the  water  which  comes  in  contact  with  these  rocks,  whether 
fresh  or  salt.  It  is,  in  fact,  the  accumulation  of  these  dissolved 
portions  which  gradually  transforms  fresh  into  salt  water.  There 
are  found  in  this  solution,  therefore,  all  the  common  metallic 
oxids  in  combination  with  all  the  common  mineral  acids. 

The  principal  mineral  bases  are  those  of  calcium,  magnesium, 
potassium,  sodium,  iron,  etc.,  and  the  principal  acid  bases  are 
chlorin,  sulfur,  boron,  carbon,  bromin,  iodin,  etc.  The  deposits  of 
these  salts  may  be  regarded  as  having  arisen  in  two  series ;  namely, 
the  original  deposit  resting  upon  a  foundation  of  rock  salt  and 
which  consisted  primarily  of  compounds  of  calcium  or  calcium 
in  conjunction  with  magnesium  and  potash.  The  pure  deposits 
of  calcium  sulfate  are  known  as  anhydiit  and  the  compounds  of 
calcium  magnesium  and  potassium  sulfate  as  polyhalit  correspond- 


THEORY  OF  DEPOSITION   OF  POTASH  SALTS  509 

ing  in  their  pure  state,  to  the  formulae  2CaSO4.MgSO4.K2SO4. 
2H2O.  These  deposits  are  found  in  alternate  layers,  having  been 
intermingled  with  rock  salt  which  diminishes  in  quantity  as  the 
deposits  approach  the  surface.  Above  these  calcium  minerals  are 
found  other  layers  in  which  magnesium  plays  the  principal  part, 
consisting  of  kieserit  MgSO4.H2O,  and  carnallit  MgCL.KCl. 
6H2O.  These  may  be  regarded  as  the  primary  or  original  de- 
posits. By  the  action  of  water  of  a  less  degree  of  concentration 
these  primary  deposits  have  been  changed,  in  some  instances,  to 
those  of  a  secondary  character,  thus  potassium  chlorid  has  evi- 
dently been  derived  by  the  action  of  water  upon  carnallit  and 
kainit.  MgSO4.KC1.3H2O  is  evidently  derived  from  carnallit  and 
kieserit. 

A  study  of  these  deposits  both  from  the  theoretic  and  practical 
point  of  view  has  been  made  by  van't  Hoff  in  which  all  the  prob- 
lems of  a  theoretic  character  relative  to  the  depositions  of  these 
compounds  are  elaborated.8 

Van't  HofT  calls  attention  to  the  fact  that  in  considering  the 
natural  depositions  of  salts  of  this  kind,  a  commonly  accepted 
principle;  namely,  that  the  least  soluble  salts  in  a  mixture  of 
this  kind  are  the  first  deposited,  is  not  necessarily  correct.9  It  is 
true  that  if  the  formation  be  considered  as  a  whole,  the  deposits 
which  take  place  naturally  must  be  in  harmony  with  the  commonly 
accepted  principle  above  stated,  and,  therefore,  that  a  slightly  solu- 
ble calcium  salt  would  first  appear  and  afterwards  the  combina- 
tion of  such  a  salt  with  more  soluble  sul fates,  then  the  easily 
soluble  magnesium  sulfates,  and  finally  comes  the  very  soluble  car- 
nallit. This  principle,  however,  assumes  that  all  the  substances  are 
present  in  a  saturated  solution.  It  is  easy  to  imagine,  however, 
that  such  would  not  be  the  case  and  that  a  more  difficultly  solu- 
ble salt  being  present  in  small  quantities  would  not,  perhaps,  be 
precipitated  as  quickly  as  a  more  easily  soluble  salt  present  in  a 
saturated  solution  at  the  temperature  of  observation.  Therefore, 
it  would  be  quite  impossible  that  there  should  be  a  solution  so  rich 
in  magnesium  sulfate,  as  van't  Hoff  states,  and  so  poor  in  gypsum 

8  Zur  Bildung  der  ozeanischen  Salzablagerungen,  1905. 

9  Physical  Chemistry  in  the  Service  of  the  Sciences,  1903  :  97. 


510  AGRICULTURAL  ANALYSIS 

that  when  concentrated,  the  more  soluble  magnesium  salt  would 
first  be  deposited.  Thus,  the  actual  composition  of  the  salt  undex" 
observation  must  be  taken  into  consideration  when  applying  the 
theory  of  the  deposition  of  salt  solutions.  A  study  of  the  order 
in  which  these  solutions  have  been  deposited  leads  to  a  knowl- 
edge not  only  of  the  relative  degree  of  saturation  of  the  original 
salt  in  the  solution  but  also  to  the  conception  of  the  temperature 
under  which  the  deposits  were  laid  down. 

If,,  in  the  theoretic  consideration  of  this  problem  some  definite 
temperature,  pressure  and  method  of  crystallization  are  assumed, 
it  is  easy  to  pass  to  a  knowledge  of  the  relative  degree  of  con- 
centration in  the  different  constituents  under  those  conditions. 
In  sea  water,  naturally  the  amount  of  sodium  chlorid  pres- 
ent is  of  the  first  consideration,  because  that  is  always  the  most 
abundant  of  the  mineral  substances  in  solution.  The  next  most 
important  mineral  constituents  are  the  salts  of  magnesium  and  po- 
tassium, especially  the  chlorids  and  sulfates  thereof,  and  the  next 
series  of  salts  to  be  considered  are  those  of  calcium.  Van't  Hoff, 
in  order  to  give  a  clearer  idea  of  this  theory,  expresses  the  propor- 
tion of  the  constituents  in  sea  water,  which  are  found  to  be,  with 
the  exception  of  calcium,  the  same  everywhere,  as  follows :  100 
NaCl+2.2KCl+7.8MgCl2-f  3.8MgSO4.  Van't  Hoff  states  that  in 
a  problem  of  this  kind  if  only  one  salt  is  present  the  situation 
is  very  simple.  When  over  two  salts  are  present  it  is  important 
to  determine  which  will  crystallize  first  and  then  when  will  the 
second  salt  begin  to  be  deposited.  This  is  illustrated  by  con- 
sidering two  common  salts ;  namely,  potassium  and  sodium  chlorid 
in  solution  at  25°.  If  potassium  chlorid  be  near  the  point  of  satura- 
tion it  will  be  the  first  to  separate  into  salt  form  and  by  further 
concentrating  the  solution  the  content  of  the  sodium  chlorid  is 
gradually  increased  until  the  saturation  point  is  reached  and  then 
it  begins  to  come  down.  Further  concentration  does  not  change 
the  present  relation  of  the  two  salts  in  solution.  They  are  both 
deposited  at  the  same  rate  when  the  saturation  point  is  reached 
and  the  evaporation  continues,  with  a  gradual  deposit  of  the  two 
salts  until  the  water  is  all  gone.  If  the  experiment  be  started  in 
the  opposite  condition  of  the  sodium  chlorid  at  saturation  point 


THEORY  OF  DEPOSITION  OF  POTASH  SALTS 


C/  f< 


Fig.  44.    Diagram  Showing  I,aw  of  Crystal- 
lization of  Potash  Salts. 


the  same  result  will  be  secured  but  in  an  inverse  order.  A  solu- 
tion which  has  been  shaken  for  a  long  time  with  an  excess  of  both 
salts  so  as  to  become  thoroughly  saturated  will  give  the  follow- 
ing composition:  iooH2O4-8o,NaCl-f-39KCl.  (C  Fig.  44). 
Thus  solutions  which  contain 
a  greater  ratio  of  sodium 
chlorid  to  potassium  chlorid 
than  89x58.5:39x74.5  will 
first  deposit  chlorid  of  sodium. 
In  the  opposite  condition  of 
the  ratio  potassium  chlorid 
will  first  appear. 

A  consideration  of  this  prob- 
lem leads  to  the  formation  of 
the  law  which  even  in  the  most 
complicated  cases  governs 
the  process  of  crystallization. 
This  law,  as  formulated  by 
van't  Hoff,  shows  that  in  depositing  its  contents,  the  solution 
gradually  varies  its  composition  away  from  that  of  a  solution 
which  is  saturated  with  the  substance  being  deposited  at  the 
moment  and  contains  nothing  but  this  substance.  The  principle 
becomes  quite  clear  if  the  process  which  takes  place  during  crys- 
tallization from  an  evaporating  solution  is  reversed  and  water  be 
continually  added  together  with  the  salt  which  is  being  deposited. 

Under  these  circumstances  obviously  the  solution  tends  to  be- 
•come  more  and  more  a  saturated  solution  of  this  salt  alone,  since 
the  other  constituents,  whatever  they  may  be,  must  gradually  be- 
come relatively  negligible  in  quantity. 

Thus,  if  a  solution  which  is  practically  that  of  sea  water  be 
•considered  corresponding  to  the  formula  for  the  salt  in  sea  water, 
already  given,  it  is  evident  that  other  salts  could  be  added  in 
order  to  change  the  degree  of  concentration.  The  principle,  how- 
ever, may  be  more  briefly  defined  if  the  case  of  potassium  chlorid, 
magnesium  chlorid,  and  magnesium  sulfate  be  first  considered  and 
only  at  the  very  end  the  chlorid  of  sodium  which  is  always  pres- 
ent in  excess  in  sea  water  be  taken  into  consideration. 


512  AGRICULTURAL   ANALYSIS 

Proceeding  in  a  systematic  manner,  attention  may  first  be  called 
to  the  combination  of  potassium  chlorid  and  magnesium  chlorid, 
that  is  to  say,  a  combination  of  these  metallic  oxids  with  a  com- 
mon acid  and  then  a  combination  of  magnesium  chlorid  and  mag- 
nesium sulfate,  that  is  a  common  base  with  different  acids.  If, 
however,  the  problem  be  stated  in  a  general  form,  potassium  sul- 
fate which  has  not  yet  been  mentioned  in  this  connection,  must  be 
taken  into  account  since  this  salt  may  be  formed  from  the  potas- 
sium chlorid  and  magnesium  sulfate  already  in  the  solution.  This 
gives  a  third  combination  of  magnesium  sulfate  and  potassium 
sulfate,  that  is,  a  combination  of  the  same  acid  with  two  metallic 
bases  and  the  last  combination  will  be  that  of  potassium  sulfate 
and  potassium  chlorid,  the  same  metallic  oxids  with  different  acids. 
In  order  to  illustrate  this  problem  graphically,  van't  Hoff  gives 
a  table  of  the  solubilities  of  these  bodies,  in  convenient  form. 

In  mols.  per  looo  mols.  H.O 
Saturation  with  K2C12     MgClj        MgSO4       K,SO4 

A.  Potassium  chlorid 44  

E.  Potassium  chlorid  and  carnallit 5.5        72.5         ....          

F.  Magnesium  chlorid  and  carnallit i         105  •  •  •  • 

B.  Magnesium  chlorid 108  

G.  Magnesium  chlorid  and  MgSO4.6H2O 104  14 

H.  MgSO4.7H2O  and  MgSO4.6H2O 73  15 

C.  MgS04.7H20 55 

J.    MgSO«.7H2O  and  schonit 58.5  5.5 

K.  Potassium  sulfate  and  schonit 22  16 

D.  Potassium  sulfate 12 

L.  Potassium  sulfate  and  potassium  chlorid  ••     42  1.5 

The  explanation  of  these  diagrams  is  best  given  in  van't 
HofT's  words: — 

"The  presentation  of  the  whole  of  this  material  graphically 
makes  the  understanding  of  it  much  easier.  The  rectangular  axes 
in  the  plane  of  the  paper  can  be  retained  and  from  their  point  of 
intersection  at  O  (Fig.  45)  the  four  single  salts,  potassium  chlo- 
rid, magnesium  chlorid,  magnesium  sulfate  and  potassium  sulfate, 
can  be  laid  off  in  the  directions,  A,B,C,  and  D,  respectively.  The 
four  combinations  which  they  form,  two  by  two,  fall  then  within 
the  quadrants  lying  between  the  axes.  We  obtain  in  this  way,. 
a  fashion  of  representing  the  facts  something  like  Fig.  44  re- 


THEORY  OF  DEPOSITION  OF  POTASH  SALTS 


513 


peated  four  times.  In  this  case,  however,  in  three  of  the  quad- 
rants a  complication  arises  from  the  existence  of  an  interme- 
diate compound.  Between  A,  saturation  with  potassium  chlorid, 
and  D,  saturation  with  potassium  sulfate,  there  is  only  the  point 
!„.  where  the  solution  is  saturated  with  both.  Between  A  and 


F 


Fig.  45.    Graphic  Representation  of  Theory  of  Crystallization. 

B,  however,  carnallit  (KCl.MgCl2.6H2O)  appears,  and  thus  two 
determinations  are  necessary,  which  have  been  added  at  E  and  F 
and  stand  for  saturation  with  carnallit  and  potassium  chlorid  in 
the  one  case,  and  the  same  compound  with  magnesium  chlorid  in 

17 


AGRICULTURAL  ANALYSIS 


the  other.  In  the  same  fashion  between  B  and  C  magnesium 
sulfate  with  six  molecules  of  water  of  crystallization  appears  in  GH 
and  between  C  and  D  the  mineral  schonit  (K2Mg(SO4)26H2O) 
along  JK.  The  progress  of  crystallization,  using  the  same  prin- 
ciple as  before,  is  just  as  easy  to  follow,  and  is  indicated  by  the 
arrows  which  in  each  quadrant  are  directed  towards  a  so-called 


Fig.  46.    Graphic  Representation  of  the  Deposition  of  Different  Salts. 

final  point  of  crystallization.     In  this  diagram  these  points  are 
F,GJ,  and  L. 

So  far,  however  we  have  only  considered  a  part  of  the  pos- 
sibilities, for  solutions  are  entirely  lacking  which  contain  every- 


THEORY  OF  DEPOSITION   OF  POTASH  SALTS  515 

thing,  that  is  to  say,  chlorin  and  sulfuric  acid,  potassium  and  mag- 
nesium. The  experimental  treatment  of  this  question  may  be  best 
shown  by  means  of  an  example.  Let  us  start  from  L  (Fig.  45), 
where  the  solution  at  25°  is  saturated  with  potassium  chlorid  and 
potassium  sulfate  simultaneously.  Taking  care  that  both  potas- 
sium salts  are  present  in  excess  and  in  contact  with  the  solution, 
we  add  magnesium  in  the  form  of  chlorid  or  sulfate.  The  solu- 
tion then  takes  up  magnesium  but  remains  still  saturated  with 
potassium  sulfate  and  potassium  chlorid.  Finally  its  capacity 
for  taking  up  magnesium  becomes  exhausted,  and  a  solid  mag- 
nesium salt  is  deposited.  This  in  the  case  before  us  is  schonit 
(K2Mg(SO4)2.6H,O).  After  this,  further  addition  of  the  mag- 
nesium salt  will  not  lead  to  any  being  dissolved ;  the  consequence 
will  simply  be  an  increase  in  the  amount  of  schonit.  The  solu- 
tion will  retain  its  constant  composition,  since  it  is  and  remains 
saturated  with  potassium  sulfate  and  potassium  chlorid.  We  de- 
termine the  composition  of  this  solution  by  analysis,  using  a  mix- 
ture which  at  25°,  after  prolonged  agitation,  is  seen  to  be  in  contact 
with  all  the  three  salts  and  is  found  to  have  attained  a  constant 
composition.  The  result  is  represented  by  the  following  formula : 

ioooH20+25K2Cl2+iiMgS04+2iMgC!8. 

Our  task  is  thus  finally  limited  to  finding  the  solutions  satura- 
ted with  three  salts  and  analyzing  those  solutions.  Many  such 
are  a  priori  possible,  if  we  consider  the  seven  different  com- 
pounds which  have  to  be  taken  into  account.  The  possible  num- 
ber would  be : 

7  X6X  5_ 
1X2X3 

As  a  matter  of  fact,  however,  only  a  few  of  these  possibilities 
are  realized,  and  when  a  solution  obtained  in  the  above  manner  is 
systematically  evaporated  at  25°,  and  the  salt  deposits  are  con- 
tinually removed,  the  possibilities  which  are  actually  realized  are 
found  to  be  limited  to  four,  in  addition  to  the  one  described. 

After  potassium  chlorid  and  schonit  have  come  out,  magnesium 


516  AGRICULTURAL  ANALYSIS 

sulfate  with  seven  molecules  of  water  of  crystallization  appears  as 
an  additional  salt.  The  deposit  having  been  removed,  this  hy- 
drate of  magnesium  sulfate  and  potassium  chlorid  is  now  depos- 
ited until  finally  magnesium  sulfate  with  six  molecules  of  water 
of  crystallization  is  added  to  these  two  salts  as  a  new  constituent. 
From  this  point  onward  the  hexahydrate  of  magnesium  sulfate 
with  potassium  chlorid  crystallizes  until  carnallit  makes  its  ap- 
pearance. After  this  the  hexahydrate  of  magnesium  sulfate  with 
carnallit  constitutes  the  deposit  until  magnesium  chlorid  appears 
and  now  the  solution  dries  up  completely  to  a  mixture  of  the  three 
last  named  substances. 

Collecting  once  more  the  quantitative  measurements  connected 
with  these  deposits,  we  have  the  following  table: 

In  mols.  per  1000  mols.  HSO 
Saturation  with  K2C1S  MgCl2  MgSO4 

M.  Potassium  chlorid,  potassium  sulfate,  schonit  25  21  n 

N.  Potassium  chlorid,  MgSO4.7H2O,  schb'nit 9  55  16 

P.  Potassium  chlorid,  MgSO4.7H2O,  MgSO4.6H,O      8  62  15 

Q.  Potassium  chlorid,  carnallit,  MgSO4.6H2O-.  •  4.5  70  13.5 

R.  Magnesium  chlorid,  carnallit,  MgSO4.6H2O- •       2  99  12 

The  next  thing  is  to  represent  these  numbers  graphically,  and 
when  this  has  been  done  we  are  presented  with  a  complete  view 
of  the  whole  process  of  crystallization. 

To  do  this  a  third  dimension  is  obviously  required.  We  add 
a  third  axis  passing  through  O,  vertical  to  the  former  system  of 
axes  (Fig.  45),  and  along  this  we  lay  off  the  number  of  molecules. 
In  practice  this  may  be  done  conveniently  by  means  of  a  model 
consisting  of  a  piece  of  wood  in  which  vertical  needles  are  set 
at  the  proper  places,  with  their  lengths  adjusted  to  the  number  of 
molecules.  A  horizontal  projection  on  this  model  is  shown  in 
Fig.  46,  whose  border  obviously  coincides  with  the  outline  of  Fig. 
45,  and  whose  points,  M,N,P,Q,  and  R,  represent  the  above  data. 
This  having  been  done,  each  pair  of  points  representing  satura- 
tion with  the  same  two  salts,  for  example,  M  and  L,  where  in 
both  cases  saturation  with  the  sulfate  and  chlorid  of  potassium 
exists,  is  connected  by  a  line. 

These  lines  divide  the  figure  into  areas,  each  of  which  corres- 
ponds to  saturation  with  a  definite  salt,  as  follows : 


THEORY  OF  DEPOSITION  OF  POTASH  SALTS  517 

EQPNMLA Potassium  chlorid 

EQRF Carnallit 

FRGB Magnesium  chlorid 

RGHPQ MgS04.6H20 

PHCJN  MgS04.7H,0 

JKMN Schonit 

KMLD Potassium  sulfate 

The  progress  of  crystallization  is  given  in  each  area  by  lines 
which  proceed  away  from  the  points  which  represent  saturation 
with  the  body  itself,  as  a  single  constituent.  Thus  in  the  potas- 
sium chlorid  area,  these  lines  proceed  from  A  in  all  directions." 

In  the  application  of  a  theory  of  this  kind  to  a  solution  con- 
taining a  gram  molecule  of  magnesium  chlorid  and  a  gram  mole- 
cule of  potassium  sulfate  the  preliminary  evaporation  before  the 
appearance  of  any  deposit  corresponds  to  motion  from  the  origin 
in  the  vertical  direction,  until  the  area  line  immediately  above  it, 
that  is,  the  potassium  sulfate  area  is  reached.  In  this  condition, 
the  potassium  sulfate  should  separate  theoretically,  and  in  fact, 
this  phenomenon  actually  occurs.  Theoretically,  the  next  move- 
ment would  begin  at  D  and  move  away  from  D  until  the  limit  KM 
is  encountered  and  at  this  point  the  separation  of  schonit  would 
begin.  The  actual  experimental  data  in  this  case  also  correspond 
with  the  theory.  If  the  salts,  as  they  separate,  are  continuous- 
ly removed,  the  deposit  of  schonit  continues  as  indicated 
in  the  figure  until  the  limit  MX  is  reached  at  which  point,  theo- 
retically a  crystallization  of  potassium  chlorid  should  take  place. 
This  theory  is  also  corroborated  by  the  experimental  data. 

When  the  point  N  is  reached  on  the  line  MN,  theoretically 
magnesium  sulfate  begins  to  be  deposited.  By  consulting  the 
table  of  the  letters  at  the  different  points  in  order  to  understand 
just  what  they  represent,  the  progress  of  crystallization  can  be 
followed  theoretically  until  the  complete  deposit  of  the  salts  takes 
place.  Thus,  the  figure,  as  worked  out  in  detail,  furnishes  a 
means  of  comprehending  the  process  of  crystallization  of  these 
mixed  salts,  and,  theoretically,  of  predicting  in  a  very  certain 
manner,  the  entire  change  which  takes  place. 

In  a  similar  manner,  van't  Hoff  has  worked  out  the  influence 
of  time  and  the  variations  of  temperature  and  pressure  on  the 


518  AGRICULTURAL,  ANALYSIS 

deposition  of  these  salts.  In  the  natural  deposition  it  is  noticed 
that  there  are  often  compounds  found  which  do  not  appear  in  lab- 
oratory experiments  but  the  deposition  of  which  can  be  theoreti- 
cally ascertained.  By  change  of  temperature,  especially  going 
above  the  fixed  standard  of  25°  on  which  the  previous  predictions 
have  been  based,  new  combinations  of  minerals  take  place  and 
minerals  which  are  formed  at  25°  disappear.  The  dominant  fac- 
tors, therefore,  in  the  order  of  crystallization  and  the  rate  of  de- 
position, are  temperature  and  concentration.  The  variations  in 
pressure  to  which  the  salts  are  subjected  doubtless  have  some 
influence  but  these  influences  are  very  minute  when  compared 
with  those  above  mentioned. 

The  agricultural  analyst  who  desires  to  study  the  causes  which 
produce  these  deposits  and  the  order  in  which  the  phenomena 
occur,  is  directed  in  the  above  epitome  of  van't  HofTs  work  to 
the  principles  which  guided  his  investigations. 

Further  details  of  the  method  of  procedure  are  found  in  the 
paper  cited. 

439.  Potash  from  Feldspathic  Rocks. — The  question  of  the 
availability  of  potash  in  feldspathic  rocks  has  been  under  discus- 
sion at  intervals  for  many  years.  The  fact  that  in  all  virgin 
soils  potash  was  originally  derived  from  the  disintegration  of  the 
rocks  is  incontestable.  It  has,  however,  been  generally  supposed 
that  such  long  periods  of  time  were  necessary  in  order  to  carry 
on  the  decompositions,  that  feldspar  could  not  be  made  practical 
use  of  as  a  potash  fertilizer.  This  impression  has  been  confirmed 
by  the  fact  that  ground  feldspar  on  digestion  with  water  yields 
only  extremely  small  amounts  of  potash  to  the  solvent.  The  sys- 
tematic investigations  of  Cushman10  have  developed  facts  of  im- 
portance in  this  connection. 

Cushman  has  shown  that  a  typical  pegmatitic  feldspar  contain- 
ing 9-3  Per  cent,  of  potash  (K2O)  when  ground  to  a  2OO-mesh 
powder,  yielded  the  following  amounts  of  potash  to  solution  in 
water,  under  varying  conditions: 

10  Bureau  of  Chemistry,    Bulletin   92,   1905;   Office   of  Public   Roads 
Circular  38  :  1905. 


POTASH  FROM  FEUDSPATHIC  ROCKS  519 

K2O,  per  cent. 

Digestion  in  distilled  water 0.03 

Grinding  with  water  in  a  mill 0.32 

Digestion  in  dilute  solution  of  ammonia  salts 0.25 

Grinding  with  same  solution 0.57 

Digestion  with  limewater 0.50 

Grinding  wet  with  calcic  sulfate 0.35 

Grinding  wet  with  lime 0.70 

Removal  of  the  alkali  by  electrolysis 0.50 

Alternative  grinding  and  electrolysis 3.50 

These  results  indicate  that  the  action  of  water  alone,  as  well 
as  the  combined  action  of  water  and  other  substances  found  in 
the  soil,  carries  on  the  decomposition  of  fine  ground  feldspar  to 
a  very  considerable  extent.  The  high  yields  of  alkali  that  can  be 
obtained  by  means  of  wet  grinding  and  electrolysis  indicate  that 
the  decomposition  might  readily  go  on  to  complete  kaolinization 
of  the  feldspar,  if  any  tendency  were  at  work  to  remove  the  de- 
composition products  from  the  surfaces  of  the  particles  upon 
which  they  are  first  formed.  Since  electrolysis  does  not  produce 
decomposition  but  merely  aids  the  water  reactions  by  removal 
of  the  decomposition  products,  it  would  seem  probable  that  in 
the  soil  this  removal  may  be  done  by  the  plant  roots  themselves, 
thus  leading  to  a  continual  and  steady  decomposition  of  the  fine 
feldspathic  particles.  Until  a  comparatively  recent  time  the  fine 
grinding  of  rocks  was  a  costly  operation,  but  the  development  of 
improved  methods  used  in  the  cement  industry  now  makes  it  pos- 
sible to  grind  rocks  to  extremely  fine  powders  at  low  cost. 

In  1850  G.  Magnus  observed  that  plants  could  be  successfully 
grown  and  matured  in  ground  feldspar,  which  apparently  suf- 
fered decomposition  during  the  process.11  In  1887  Aitken  in 
Scotland  conducted  successful  plat  experiments  on  a  small 
scale,  using  Norwegian  feldspathic  rock  rich  in  potash,  ground  to 
I2o-mesh  powder.12  Peas  and  turnips  were  the  crops  used,  and  in 
all  cases  an  increased  yield  was  obtained  as  the  result  of  the  use 
of  feldspar. 

11  Journal  fur  praktische  Chemie,  1850,  50  :  65. 

11  Highland  and  Agricultural   Society  of  Scotland,  Transactions,  1887, 
19  :  253- 


52O  AGRICULTURAL  ANALYSIS 

In  1889  the  Maine  State  College  Experiment  Station  success- 
fully grew  oats  in  plats  using  ground  feldspar  in  connection  with 
nitrate  of  soda  and  superphosphate.13  In  1890  Headden  in  Colo- 
rado carried  on  a  similar  set  of  experiments  on  oats.14  The  conclu- 
sion was  reached  that  the  oat  plant  can  use  finely  divided  feldspar 
as  a  source  of  potash. 

At  about  the  same  time  Hensel  in  Germany  was  advocating  the 
use  of  stone  meal  as  a  fertilizing  agent.  Conflicting  reports  have 
been  made  as  to  the  results  of  these  experiments,  and  in  any  case 
it  would  appear  that  the  material  used  had  not  been  ground  fine 
enough  to  render  it  quickly  available. 

The  investigations  of  Cushman  have  reopened  the  question  and 
systematic  experiments  are  under  way  which  should  settle  this 
important  question  once  and  for  all.  E^en  should  it  appear  that 
such  material  is  directly  useful  as  a  fertilizer,  the  question  as  to 
its  wide  spread  use  will  necessarily  depend  upon  the  cost  in- 
volved in  grinding  and  transporting  it. 

440.  Cushman's  Later  Investigations. — Investigation  of  the 
availability  of  potash  in  feldspathic  rocks  has  been  continued  by 
Cushman  in  connection  with  the  experiments  in  the  actual  grow- 
ing of  crops.15  He  finds  that  a  cubic  foot  of  granite  weighs 
about  170  pounds  and  contains  about  8.5  pounds  of  potash,  and 
that  loo  feet  square  and  100  feet  in  depth  will  contain  about 
8,500,000  pounds  of  potash.  It  is  evident,  therefore,  that  feld- 
spathic rock  which  is  accessible  in  the  United  States  would  af- 
ford an  almost  inexhaustible  supply  of  potash  if  it  could  be  util- 
ized. Very  large  deposits  of  this  feldspathic  rock  are  found  in 
various  parts  of  the  country,  and  these  have  been  developed  for 
building  and  other  purposes  in  Maine,  Connecticut,  Pennsylvania 
and  Maryland.  The  feldspathic  rocks  obtained  from  these  mines 
have  been  ground  to  fine  powders,  chiefly  for  use  in  potteries. 

Orthophyric  feldspathic  rock  contains  16.8%  of  potash,  but 
the  feldspar  from  the  sources  above  mentioned  contains  only 
from  8%  to  10%. 

Cushman  says : 

13  Annual  Report  of  the  Maine  State  College  Agricultural  Experiment 
Station,  1889  :  143. 

14  Colorado  Agricultural  Experiment  Station,  Bulletin  65,  1901  :  28. 

15  Bureau  of  Plant  Industry,  Bulletin  104,  1907. 


CUSHMAN'S  LATER  INVESTIGATIONS  521 

"The  question  whether  fine-ground  feldspar  can  be  used  as 
a  potash  fertilizer  has  been  a  matter  of  controversy  for  many 
years.  There  is  a  large  and  widely  scattered  literature  on  the 
subject,  an  examination  of  which  shows  that  the  matter  has 
been  debated  with  much  vigor  and  sometimes  with  prejudice  and 
intolerance  on  both  sides.  It  is  easy  to  find  the  published  re- 
cords of  a  number  of  experiments,  made  by  trained  and  thor- 
oughly competent  agriculturists,  which  tend  to  show  that  ground 
feldspar  is  an  efficient  potash  fertilizer.  On  the  other  hand,  a 
number  of  experiments  seem  to  indicate  that  the  potash  is  only 
slightly  available,  while  others  would  appear  to  show  that  the 
ground  rock  is  entirely  useless.  On  account  of  the  large  inter- 
ests involved  in  the  settlement  of  this  question  it  is  not  difficult 
to  see  why  vigorous  differences  of  opinion,  and  even  unjust 
prejudice  should  have  arisen.  When,  however,  trained  investi- 
gators reach  opposite  conclusions,  based  upon  experimental  evi- 
dence, we  are  forced  to  the  opinion  that  while  ground  feldspar 
may  be  a  useful  fertilizer  under  certain  conditions  it  is  not  so 
under  others." 

Very  full  reference  to  the  literature  of  the  availability  of  rock 
potash  is  given  by  Cushman  in  the  work  above  cited,  and  in 
addition  to  these  data  experiments  were  undertaken  by  him  to 
test  anew  the  value  of  the  fine-ground  rocks  for  this  purpose. 
Tobacco  was  selected  as  the  plant  most  suitable  for  the  experi- 
ment, because  it  is  one  of  those  plants  which  requires  a  very 
large  quantity  of  potash  for  its  proper  nourishment.  Artificial 
soils  were  prepared  having  for  a  base  coarse  grained  white  sand 
and  finely  ground  feldspar  containing  about  8  per  cent,  of  potash. 
Seedlings  were  set  out  in  this  mixture  and  moistened  from  time 
to  time  with  solutions  of  ammonium  nitrate  and  ammonium 
phosphate  in  order  to  supply  the  necessary  amount  of  nitrogen 
and  phosphoric  acid. 

In  addition  to  these  field  experiments  others  were  made  in  a 
green  house,  in  which  the  effect  of  potassium  in  the  form  of 
carbonate  containing  about  67  per  cent,  of  potash  was  compared 
with  the  potash  in  fine-ground  feldspar,  containing  about  8.3 
per  cent  of  potash. 


522  AGRICULTURAL  ANALYSIS 

In  addition  a  third  experimental  plot  was  prepared,  to  which 
no  potash  was  added.  All  three  beds  were  supplied  with  a 
sufficient  quantity  of  nitrogen  for  the  purposes  of  crop  growth 
in  the  form  of  ammonium  nitrate. 

After  the  harvesting  of  the  crop  the  data  were  collected  with 
the  following  results : 

RESULTS  OF  GREENHOUSE  EXPERIMENTS  WITH  TOBACCO  PLANTS. 


No.                                                      Actual 
of           Source  of  potash.          weight  of 
plat.                                               green  crop. 
Pounds. 

Estimated 
weight  of 
green  crop 
per  acre. 
Pounds. 

Actual 
•weight  of 
cured  leaf. 
Pounds. 

Estimated 
weight  of 
cured  leaf 
per  acre. 
Pounds. 

i     Potassium   carbonate     154.0 

30,800 

5-70 

1,140 

2     Ground  feldspar  i55-o 
i                                              128.1; 

31,000 

21.7OO 

6.30 

S.7O 

I,26o 
i.nfio 

Cushman  calls  attention  to  the  fact  that  these  yields  are  not 
equal  to  those  obtained  in  the  field  under  good  conditions,  but 
are  satisfactory  for  a  winter  crop  in  a  green  house. 

441.  The  Effect  of  Fineness  of  Grinding. — In  the  study  of  these 
experiments  the  theoretical  contention  on  which  is  based  the  idea 
that  the  fineness  of  the  grinding  is  to  some  extent  the  measure  of 
the  availability  of  the  feldspar  in  feldspathic  rocks  was  thor- 
oughly tested.     The  conclusion  is  that  the  potash  in  these  rocks 
is  partially  available  even  during  the  first  season,  but  that  the 
availability  in  the  coarse  particles  is  not  very  great,  hence  fine- 
ness of  grinding  is  not  only  a  necessary  condition  to  the  utiliza- 
tion of  the  potash,  but  time   is  also   an  important   factor.     It 
would  be  unwise  in  the  present  state  of  our  knowledge  to  depend 
upon  the  finely  ground  potash  alone  for  the  production  of  a 
large  crop.     It  is  wiser  to  add  during  the  first  years  at  least  a 
sufficient  quantity  of  more  available  potash  to  supply  the  needs 
of  the  crop  until  the  weathering  of  the  finely  ground  rock  has 
somewhat  progressed. 

The  problem  of  cost  is  also  an  important  factor  in  these  in- 
vestigations. Unless  feldspar  can  be  reduced  to  a  fine  powder, 
transported  and  sold  at  a  small  price  per  ton,  it  is  evident  that  at 
least  for  the  present  it  can  not  play  any  important  role  as  a  plant 
food. 

442.  Mills  for  Grinding. — The  mills  which  are  used  for  grind- 


MILLS  FOR  GRINDING  .  523 

ing  feldspar  for  the  pottery  would  also  be  suitable  for  preparing 
it   for  agricultural  purposes.     Cushman   says: 

"For  fertilizer  purposes  the  fine  grinding  of  feldspar  could  be 
done  in  iron  mills  similar  to  those  which  are  used  for  grinding 
limestone  in  the  cement  industry.  The  only  important  points  to 
consider  would  be  the  percentage  of  total  potash  present  and  the 
fineness  of  grinding.  At  the  present  time  there  are  few  data 
available  on  the  cost  of  grinding  feldspar  to  a  2OO-mesh  powder, 
but  with  modern  machinery  there  is  little  doubt  that  it  can  be 
done  much  more  economically  than  would  have  been  considered 
possible  only  a  few  years  ago.  Under  the  stimulus  of  the  cement 
industry  a  great  development  has  been  made  in  recent  years  in 
the  methods  and  art  of  fine  grinding.  The  following  table  is 
of  interest,  as  it  shows  at  a  glance  what  the  potash  in  ground 
feldspar  would  cost  if  the  percentage  is  compared  with  a  cost 
of  grinding  varying  from  $i  to  $10  per  long  ton. 

PRICE  PER  POUND  OF  POTASH  UNIT  IN  FELDSPAR. 


Potash  contained 

Cost  of  ground  feldspar  per  ton  (2,240  pounds). 

in  the  feldspar. 

$i. 

$2. 

J3- 

$4- 

$5- 

$6. 

$7- 

$8. 

19- 

$10. 

3  per  cent.  .  .  . 

$0.015 

$0.030 

$0.044 

$0-059 

$0.074 

$0.089 

$0.104 

$0.119 

Jo-  '34 

$0.149 

4  per  cent.  .   .   . 

.Oil 

.022 

•°33 

.044 

•055 

.067 

.078 

.089 

.100 

.III 

5  per  cent.  .   .   . 

.009 

.018 

.027 

•035 

.044 

•053 

.062 

.071 

.080 

.090 

6  per  cent.  .  .   . 

.007 

•0'5 

.022 

.030 

•037 

•045 

•052 

•059 

.067 

.074 

7  per  cent.  .  .  . 

.006 

.012 

.019 

.025 

•03* 

.038 

•045 

-051 

•057 

.063 

8  per  cent.  .   .   . 

.005 

.Oil 

.017 

.022 

.028 

.032 

•039 

-045 

.050 

.056 

9  per  cent.  .   .   . 

.005 

.009 

.014 

.019 

.024 

.029 

•035 

•039 

.044 

.049 

10  per  cent.  .  .  . 

.004 

.009 

•015 

.018 

.022 

.027 

•031 

.035 

.040 

•045 

ii  per  cent.  .  .   . 

.004 

.008 

.on 

•015 

.020 

.023 

.028 

.030 

.024 

.040 

12  per  cent.  .  .  . 

.004 

.007 

.Oil 

•015 

.018 

.022 

.026 

.029 

•033 

•037 

13  per  cent.  .  .   . 

.003 

.007 

.010 

.014 

.017 

.021 

.024 

.027 

•031 

-034 

14  per  cent.  .  .  . 

.003 

.006 

.010 

•013 

.Ol6 

.019 

.022 

.026 

.029 

•03* 

15  per  cent.  .  .  . 

•0°3 

.006 

.009 

.012 

-015 

.018 

.021 

.024 

.027 

.030 

The  prices  are  given  in  cents  per  pound,  so  that  if,  for  in- 
stance, rock  carrying  eight  per  cent,  of  potash  could  be  de- 
livered for  $9  per  ton,  the  potash  contained  in  it  would  be  added 
to  the  land  at  a  cost  of  5  cents  per  pound.  At  $5  per  ton  the 
cost  per  pound  would  fall  to  28  mills.  The  figures  are  of  course 
only  applicable  provided  the  potash  in  the  ground  material  can 
be  proved  available  as  a  plant  food." 

On  this  subject  Cushman  makes  the  following  observation: 
"It  must  be  remembered  that  the  only  real  measure  of  avail- 
able potash  is  that  which  is  made  use  of  by  the  crop.     It  is  not 


524  AGRICULTURAL  ANALYSIS 

likely  that  all  the  potash  added,  even  in  the  form  of  soluble 
potash  salts,  is  actually  used,  and  the  amount  that  can  be  sup- 
plied by  ground  rock  is  still  an  unknown  quantity." 

The  quantity  of  feldspar  ground  in  short  tons  and  the  cost 
of  production  is  given  in  the  following  table  for  the  years  1901- 
5  inclusive: 

PRODUCTION  AND  VALUE  OF  FELDSPAR,  1901-1905. 

[Short  Tons] . 

Crude.  Ground.  Total. 

Year  Quantity.          Value.          Quantity.  Value.          Quantity.          Value. 

I9CI 9,960  $21,669  24,781  $198,753  34.741  $220,422 

1902 21,870  55,501  23,417  194,923  45,287  250,424 

I9°3 13,432  51,036  28,459  205,697  41,891  256,733. 

1904 19,413  66,714  25,775  199,612  45,188  266,326 

1905 14,517  57,976  20,902  I68,l8l  35,419  226,157 

443.  Possible  Harmful  Effects  of  Ground  Feldspar. — "The  ques- 
tion is  frequently  asked  whether  there  is  possible  danger  to  the 
land  in  experimenting  with  the  use  of  ground  feldspathic  rock. 
It  is  well  known  that  in  some  cases,  notably  with  tobacco,  in- 
jurious effects  are  produced  by  the  continued  use  of  the  soluble 
potash   salts,   particularly  the   sulphate  and   muriate.     Feldspar 
grains  of  various  sizes  are  normally  present  in  many  soils;  it 
does  not,  therefore,  seem  possible  that  any  harmful  effect  could 
follow  the  application  of  ground  rock.     As  has  been  pointed  out 
in  an  earlier  portion  of  this  paper,  feldspar  consists  of  the  al- 
kaline elements,  soda,  potash,  and  lime,  combined  with  alumina 
and  silica.     After  decomposition,  hydrated  aluminum  silicate,  the 
essential  base  of  all  clays,  is  left  behind,  the  alkalies  and  the 
silica  being  set  free  in  a  condition  in  which  they  can  be  ab- 
sorbed by  the  root  action  of  plants.     It  would  seem,  therefore, 
that  whatever  the  value  of  the  results  obtained  no  possible  harm 
can  follow  the  experimental  use  of  ground  felspar  in  reasonable 
quantities." 

444.  Extract  of  Potash  from  Ground  Rock. — "The  discussion  of 
the  use  of  ground  rock  as  a  source  of  potash  is  not  complete 
unless  it  includes  the  extraction  of  potash  by  chemical  and  elec- 
trical processes.     If  future  experiments  should  demonstrate  that 
fast-growing   crops   are    dependent   on    very   soluble    forms   of 


CONCLUSION  525 

potash  the  question  of  the  extraction  of  this  element  from  ground 
feldspar  becomes  a  matter  of  importance. 

The  extraction  of  potash  from  rock  has  not  as  yet  been  ac- 
complished on  a  commercial  basis,  but  it  has  been  done  in  the 
laboratory,  and  the  method  has  been  published  in  a  recent  bul- 
letin.16 The  full  details  of  the  investigation  are  too  technical 
for  insertion  here,  but  if  the  processes  described  could  be  car- 
ried on  at  a  cost  low  enough,  the  potash  in  ground  rock  could  be 
rendered  sufficiently  soluble  for  all  practical  purposes.  Brief- 
ly, the  method  consists  in  sliming  the  ground  feldspar  with 
water  to  which  a  small  quantity  of  hydrofluoric  acid  has  been 
added.  This  slime  is  placed  inside  a  suitable  wooden  vessel 
and  a  current  of  electricity  is  passed  through  it.  The  alkali  set 
free  by  the  action  of  the  acid  is  carried  away  by  the  electric 
current,  while  the  acid  appears  to  be  used  over  and  over  again. 
Finally,  by  combining  the  acid  and  alkaline  products,  a  material 
is  obtained  in  which  the  potash  which  has  been  set  free  is  solu- 
ble and  available. 

A  number  of  methods  for  extracting  potash  from  feldspathic 
rocks  by  means  of  fusions  with  various  substances  have 
been  devised  and  even  patented.  In  all  of  these  methods, 
however,  large  quantities  of  by-products  are  formed  which, 
though  made  from  more  or  less  costly  material,  are  generally  of 
no  value.  From  laboratory  investigations  it  would  seem  that  the 
use  of  potash  compounds  to  attack  the  feldspar  would  in  some 
measure  overcome  this  difficulty,  since  the  potash  used  is  just  as 
valuable  after  the  process  is  completed  as  it  was  before.  An- 
other method,  which  shows  some  promise  of  success  consists  in 
mixing  the  feldspar  with  lime  and  treating  the  mixture  with 
live  steam  under  pressure.  By  this  means  the  potash  is  made 
easily  acid  soluble.  It  is  hoped  that  further  investigation  will  re- 
sult in  some  method  based  on  these  principles  for  making  the 
vast  quantities  of  potash  contained  in  feldspathic  rocks  com- 
pletely available." 

445.  Conclusion. — "A  careful  reading  of  the  foregoing  pages 
will  show  that  no  claim  has  been  made  that  ground  feldspar  is 
an  efficient  substitute,  under  all  circumstances,  for  potash  salts. 
16  Bui.  28,  U.  S.  Dept.  of  Agriculture,  Office  of  Public  Roads. 


526  AGRICULTURAL   ANALYSIS 

The  effort  has  been  to  present  all  the  evidence  which  could  be 
collected,  both  for  and  against  the  use  of  ground  feldspar  as  a 
fertilizer.  The  question  is  still  open,  and  systematic  and  long- 
continued  experimentation  is  the  only  possible  method  of  ob- 
taining conclusive  information  on  the  subject.  The  evidence  so 
far  obtained  appears  to  indicate  that  under  certain  conditions 
and  with  certain  crops  feldspar  can  be  made  useful  if  it  is 
ground  sufficiently  fine.  On  the  other  hand,  it  is  highly  proba- 
ble that  under  other  conditions  the  addition  of  ground  feldspar 
to  the  land  would  be  a  useless  waste  of  money.  At  the  present 
stage  of  the  investigation  it  would  be  extremely  unwise  for 
anyone  to  attempt  to  use  ground  rock,  except  on  an  experimental 
scale  that  would  not  entail  great  financial  loss. 

The  subject  must  be  approached  conservatively,  with  due  re- 
gard to  business  economy.  Sensationalism  and  exaggeration  in- 
variably do  harm.  It  is  extremely  unlikely  that  ground  rock 
will  ever  entirely  displace  the  use  of  potash  salts  for  its  availa- 
bility must  inevitably  depend  upon  many  modifying  conditions, 
such  as  the  nature  of  the  soil,  the  amount  of  moisture  present, 
the  character  of  the  other  fertilizers  used,  and  the  varying  root 
action  of  different  crops.  With  tobacco  the  results  so  far  ob- 
tained have  been  encouraging,  but  it  is  possible  that  this  plant, 
which  is  a  voracious  feeder,  can  make  use  of  the  potash  in  fine- 
ground  feldspar  to  a  greater  extent  than  any  other  fast-growing 
crops,  such  as  potatoes  and  the  cereals,  some  of  which  mature 
in  practically  sixty  days  and  must  therefore  find  their  plant  food 
in  a  highly  available  condition." 

ORGANIC  SOURCES  OF  POTASH 

446.  Tobacco  Stems  and  Waste. — Until  within  a  few  years 
tobacco  stems  and  other  waste  from  factories,  were  treated  as  a 
nuisance  in  this  country  and  burned  or  dumped  into  streams. 
By  burning  and  saving  the  ash,  the  potash  contained  in  the  stems 
and  waste  is  recovered  in  a  form  suitable  for  field  use.  The 
nitrogen  contained  in  these  waste  materials,  both  in  the  form 
of  nicotin  and  of  albuminoids  is  lost.  Ignition  of  this  waste 
should  not  be  practiced.  It  should  be  prepared  for  use  by  grind- 
ing to  a  fine  powder.  Applied  to  the  soil  in  this  condition  the 


TOBACCO    STEMS    AND    WASTE  527 

powder  may  be  useful  as  an  insecticide  as  well  as  a  fertilizer.  To- 
bacco stems  contain  from  12  to  27  per  cent,  of  moisture,  and  from 
12  to  20  per  cent,  of  ash.  The  composition  of  the  stems  from  two 
celebrated  tobacco-growing  regions  is  subjoined:17 

Kentucky  stems       Connecticut  stems 
per  cent.  per  cent. 

Moisture 26.70  13-47 

Organic  and  volatile 60. 18  70.85 

Ash 13.12  15.68 

The  ash  calculated  to  the  original  substance  has  the  following 
composition : 

Kentucky  stems  Connecticut  stems 
per  cent.  per  cent. 

Phosphoric  acid  •< 0.67  0.53 

Potash 8.03  6.41 

It  is  thus  seen  that  about  half  the  ash  of  tobacco  stems  is  com- 
posed of  potash.  The  stalks  of  the  tobacco  have  almost  the  same 
•composition  as  the  stems,  but  the  percentage  of  ash  is  not  quite 
so  great.  In  three  samples  analyzed  at  the  Connecticut  station 
the  percentages  of  ash  found  in  the  water-free  substance  are  6.64, 
7.00,  and  7.46,  respectively.  The  pure  ash  of  the  stalks  is  found 
to  have  the  following  composition:18 

Description  of  samples. 
Cut  Aug.  22,       Cut  Sept.  17, 
Constituents  per  cent.  per  cent. 

Silica 0.82  0.57 

Iron  and  aluminum  oxids 1.38  1.38 

Lime 14.01  16.58 

Magnesia 6.64  7.36 

Potash 56.34  54-46 

Soda 1.28  1.16 

Sulfuric  acid 8.06  6.75 

Phosphoric  acid 6.37  6.27 

Chlorin 6.55  7.05 

101.45  101.58 

Deduct  oxygen  =  chlorin 1.48  1.58 

IOO.OO  IOO.OO 

The  leaves  of  the  tobacco  contain  more  ash  than  the  stalks  or 
stems,  but  the  percentage  of  potash  therein  is  less.     In  18  samples 

17  Connecticut  Agricultural  Experiment  Station,  Bulletin  97,  1889  :  7. 

18  Annual  Report  of  the  Connecticut  Agricultural  Station,  1892  :  32. 


528  AGRICULTURAL   ANALYSIS 

analyzed  at  the  Colorado  station  the  percentages  of  moisture  in 
the  leaf  varied  from  6.08  to  28.00,  and  those  of  ash  from  22.60  to 
28.OO.19  The  percentages  of  potash  in  the  ash  varied  from  15.20 
to  26.30.  In  these  data  the  carbon  dioxid,  sand,  etc.,  are  included 
while  in  those  quoted  from  the  Connecticut  station  they  are  ex- 
cluded. 

447.  Cottonseed  Hulls  and  Meal. — A  considerable  quantity  of 
potash  is  added  to  the  soil  in  cottonseed  meal  and  hulls.  The 
practice  of  burning  the  hulls  cannot  be  recommended,  although 
it  is  frequently  done,  for  the  incineration  does  not  increase 
the  quantities  of  phosphoric  acid  and  potash,  while  it  destroys 
the  availability  of  the  nitrogen.  Nevertheless,  the  analyst  will 
often  have  to  deal  with  samples  of  the  raw  materials  above  men- 
tioned, as  well  as  with  the  ash  of  the  hulls,  in  which  the  potash 
can  be  determined  by  some  one  of  the  standard  methods  to  be 
described.  In  general  it  is  found  that  the  hulls  of  seeds  and  the 
bark  and  leaves  of  plants  have  a  greater  percentage  of  ash 
than  the  interior  portions.  In  the  case  of  cottonseed,  how- 
ever, an  exception  is  to  be  noted.  The  cottonseed  meal  in  the 
air-dried  state  has  about  seven  per  cent,  of  ash,  while  the  hulls 
have  only  about  three.  When  it  is  remembered,  however,  that 
the  greater  part  of  the  oil  has  been  removed  from  the  meal  it  will 
be  seen  that  in  the  whole  seed  in  the  fresh  state  the  discrepancy 
is  not  so  marked. 

In  the  crude  ash  of  the  hulls  the  percentage  of  potash  varies 
generally  from  20  to  25,  but  in  numerous  cases  these 
limits  are  exceeded.  In  12  samples  of  cottonseed  hull  ashes 
examined  by  the  Connecticut  station  the  mean  percentage  of 
potash  in  the  crude  sample  was  22.47,  anc^  tne  extremes  15.57 
and  30.24  per  cent.,  respectively.20  In  determining  the  value  of 
the  ash  per  ton  the  content  of  phosphoric  acid  must  also  be  taken 
into  account. 

Cottonseed  meal  contains  about  1.75  per  cent  of  potash.  Since 
the  mean  percentage  of  ash  in  the  meal  is  seven,  the  mean  con- 
tent of  potash  in  the  crude  ash  is  about  25. 

19  Colorado  Agricultural  Experiment  Station,  Bulletin  10,  1890  :  13. 
w  Connecticut  Agricultural  Experiment  Station,  Bulletin  103,  1890  :  9. 


WOOD  ASHES  529 

448.  Wood  Ashes. — Unleached  wood  ashes  furnish  an  im- 
portant quantity  of  potash  fertilizer.  The  composition  of  the 
ash  of  woods  is  extremely  variable.  Not  only  do  different  varie- 
ties of  trees  have  varying  quantities  of  ash,  but  in  the  same 
variety  the  bark  and  twigs  will  give  an  ash  quite  different  in 
quantity  and  composition  from  that  furnished  by  the  wood  itself. 
In  general  the  hard  woods,  such  as  hickory,  oak,  and  maple, 
furnish  a  quality  of  ash  superior  for  fertilizing  purposes  to  that 
afforded  by  the  soft  woods,  such  as  the  pine  and  birch  trees. 

The  character  of  the  unleached  wood  ashes  found  in  the  trade 
is  indicated  by  the  subjoined  analyses.  The  first  table  contains 
the  mean,  maximum  and  minimum  results  of  the  analyses  of 
97  samples  by  Goessmann.21 

Composition  of  wood  ashes. 
Means        Maxima        Minima 

Potash 5-5  io-2  2.5 

Phosphoric  acid 1.9  4-°  °-3 

Lime 34'4  5°-9  l8-° 

Magnesia 3-5  7-5  2-3 

Insoluble 12.9  27.9  2.1 

Moisture 12.0  28.6  0.7 

Carbon  dioxid  and  undetermined 29.9 

In  1 6  analyses  made  at  the  Connecticut  station  the  data  ob- 
tained are  given  below:22 

Means        Maxima        Minima 

Potash 5-3  7-7  4-0 

Phosphoric  acid i-4  *-8  i-9 

In  15  analyses  of  ashes  from  domestic  wood-fires  in  New  Eng- 
land, the  following  mean  percentages  of  potash  and  phosphoric 
acid  were  found: 

Potash 9-63 

Phosphoric  acid 2'32       , 

In  leaching,  ashes  lose  chiefly  the  potassium  carbonate  and 
phosphate  which  they  contain.  Leached  and  unleached  Canada 
ashes  have  the  following  composition: 

21  Annual  Report  of  the  Massachusetts  Agricultural  Experiment  Station, 

1888  :  202. 

"  Annual  Report  of  the  Connecticut  Agricultural  Experiment  Station , 

1889  :  no. 


530  AGRICULTURAL   ANALYSIS 

Unleached        I,eached 
per  cent.         per  cent. 

Insoluble 13.0  13.0 

Moisture 12.0  30.0 

Calcium  carbonate  and  hydroxid 61.0  51.0 

Potassium  carbonate 5.5  i.i 

Phosphoric  acid 1.9  1.4 

Undetermined 6.6  3.5 

In  the  wood  ashes  of  commerce,  it  is  evident  that  the  propor- 
tion of  the  potash  to  the  lime  is  relatively  low. 

The  number  of  parts  by  weight  of  the  chief  ingredients  of  the 
ash  in  10,000  pounds  of  woods  of  different  kinds  is  given  in  the 
table  page  531,  with  the  percentage  composition  of  the  pure 
ash,  that  is  the  crude  ash  deprived  of  carbon  and  carbon  dioxid. 

449.  Statement  of  Results. — The  bases  which  are  found  pres- 
ent in  the  ashes  of  wood  and  other  vegetable  tissues  exist  with- 
out doubt  before  incineration,  chiefly  in  combination  with  in- 
organic acids.  Even  the  phosphorus  and  sulfur  which  after  igni- 
tion appear  as  phosphates  and  sulfates,  have  previous  thereto 
existed  in  an  organic  form  to  a  large  extent.  The  silica  itself 
is  profoundly  modified  in  the  organism  of  the  growing  plant,  and 
possibly  may  not  exist  there  in  the  purely  mineral  form  in 
which  it  is  found  in  the  ash.  During  the  progress  of  incineration, 
with  proper  precautions,  all  the  phosphorus  and  sulfur  are  oxi- 
dized and  appear  as  phosphoric  and  sulfuric  acids.  The  silica  is 
reduced  to  a  mineral  state,  and  if  a  high  heat  be  employed  sili- 
cates are  formed.  The  organic  salts  of  lime,  magnesia  and  other 
bases  at  a  low  temperature  are  converted  into  carbonates,  and  if 
a  higher  temperature  be  used,  may  appear  as  oxids.  The  organic 
compounds  of  alkalies  will  be  found  in  the  ash  as  carbonates. 
It  would  be  useless,  therefore,  to  try  to  state  the  results  of  ash 
analysis  in  forms  of  combination  similar  to  those  existing  in  the 
original  vegetable  tissues.  It  is  not  certain  even  that  we  can  in 
all  cases  judge  of  the  form  of  combination  in  which  the  different 
constituents  exist  in  the  ash  itself.  It  is,  therefore,  to  be  pre- 
ferred in  a  statement  of  ash  analysis  to  give  the  bases  in  the 
form  of  oxids,  and  the  sulfur  and  phosphorus  in  the  form  of  an- 
hydrides, and  the  chlorin  in  its  elementary  state.  In  this  case  an 


STATEMENT   OF    RESULTS 


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532  AGRICULTURAL   ANALYSIS 

equivalent  amount  of  oxygen  to  the  chlorin  found  must  be  sub- 
tracted from  the  total.  If  an  attempt  be  made  to  combine  the 
acid  and  basic  elements,  the  chlorin  should  first  be  united  with 
sodium,  and  any  excess  thereof  with  potassium,  and  the  amount 
of  base  so  combined  calculated  to  oxid  and  deducted  from  the 
total  of  such  base  or  bases  present.  The  carbonic  acid  present 
should  be  combined  first  with  alkalies  after  the  chlorin  has  been 
supplied.  The  phosphoric  acid  should  be  combined  first  with 
the  iron  and  afterwards  with  lime  or  magnesia.  In  all  cases 
the  percentages  should  be  based  upon  the  ash,  after  the  carbon 
and  sand  have  been  deducted,  or  it  is  also  convenient  at  times  to 
throw  out  of  the  results  the  carbon  dioxid  and  to  calculate  the 
other  constituents  to  the  ash  free  of  that  substance.  In  deter- 
mining the  quantities  of  mineral  matters  removed  from  soil  by 
crops,  the  ash  should  be  determined  with  great  care,  freed  of 
carbon  and  sand,  and  the  calculations  made  on  the  percentage 
thus  secured.  In  all  statements  of  percentages  of  the  essential 
constituents  of  ash,  as  regards  fertilizing  materials,  it  should  be 
specified  whether  the  percentage  is  calculated  on  a  crude  ash, 
the  pure  ash,  that  is  free  of  carbon  and  sand,  or  upon  a  basis 
excluding  the  carbon  dioxid.  For  the  purpose  of  fertilizer  control 
the  analyst  and  dealer  will  be  satisfied,  as  a  rule,  with  the  deter- 
mination of  the  percentages  of  phosphoric  acid  and  potash  alone. 
To  the  other  constituents  of  an  ash  is  not  assigned  any  commer- 
cial value. 

450.  Fertilizing  Value  of  Ashes. — Primarily,  the  fertilizing 
value  of  wood-ashes  depends  on  the  quantity  of  plant  food  which 
they  contain.  With  the  exception  of  lime,  potash,  and  phosphoric 
acid,  however,  the  constituents  of  wood-ashes  have  little,  if  any, 
commercial  value.  The  beneficial  effects  following  the  applica- 
tion of  ashes,  however,  are  greater  than  would  be  produced  by  the 
same  quantities  of  matter  added  in  a  purely  manurial  state.  The 
organic  origin  of  these  materials  in  the  ash  has  caused  them  to 
be  presented  to  the  plant  in  a  form  peculiarly  suited  for  absorp- 
tion. Land  treated  generally  'with  wood-ashes  becomes  more 
amenable  to  culture,  is  readily  kept  in  good  tilth,  and  thus 
retains  moisture  in  dry  seasons  and  permits  of  easy  drainage  in 


MOLASSES    FROM    SUGAR-BEETS  533 

wet.  These  effects  are  probably  due  to  the  lime  content  of  the 
ash,  a  property  moreover  favorable  to  nitrification  and  adapted 
to  correcting  acidity.  Injurious  iron  salts,  which  are  sometimes 
found  in  wet  and  sour  lands,  are  precipitated  by  the  ash  and 
rendered  innocuous  or  even  beneficial.  A  good  wood-ash  fer- 
tilizer, therefore,  is  worth  more  than  would  be  indicated  by  its 
commercial  value  calculated  in  the  usual  way. 

451.  Availability  of  Ash  Potash. — Harcourt  has  determined  the 
availability  of  the  potash  of  wood-ashes  by  the  citric  acid  method 
of  Dyer.23 

It  has  been  stated  by  those  interested  in  the  sale  of  potash  fer- 
tilizers that  the  potash  in  wood-ashes  is  not  all  in  an  available 
form,  i.  e.,  part  of  it  is  insoluble  and  is,  therefore,  of  no  use  to 
the  plant.  To  ascertain  what  truth  there  is  in  the  statement,  a 
number  of  ashes  was  treated  by  Dyer's  method  for  determining 
availability  of  plant  food.  The  following  table  gives  the  number 
of  pounds  of  potash  and  the  amount  that  would  be  immediately 
available  in  100  pounds  of  the  different  ashes  examined. 

Pounds  of        Pounds  of  potash        Per  cent. 

potash  in  available  in  100          of  potash 

Name  of  ash  100  Ibs.  ash  Ibs.  ash  available 

White  oak 9.39  7-64  82.33 

Birch 8.58  6.82  79.48 

Mixed  ash 13.40  12.72  94.92 

Walnut 4-62  4.61  99.87 

Red  oak 5-75  4-?2  82.09 

Poplar 10.42  8.78  84.26 

White  ash 16.88  15.24  90.20 

Butternut 3.99  3-56  89.22 

Willow 9-59  8.19  85.40 

Average 87.50 

According  to  this  method  nearly  80  per  cent,  of  the  total  potash 
of  the  birch  ash,  and,  practically,  all  that  of  the  walnut  ash,  or  an 
average  of  87.5  per  cent,  of  the  potash  of  all  the  ashes  examined 
was  found  to  be  immediately  available.  In  other  words,  an  aver- 
age of  the  nine  samples  experimented  with  shows  that  all  but  12.5 
per  cent,  of  the  total  potash  would  be  in  a  form  of  which  the 
growing  plant  could  make  use  at  once. 

452.  Molasses   from   Sugar-Beets. — The   residual   molasses   re- 
»  Ontario  Agricultural  College,  23rd  Annual  Report,  1897  :  27. 


534  AGRICULTURAL  ANALYSIS 

suiting  after  the  extraction  of  all  the  crystallizable  sugar  in 
beet-sugar  manufacture  is  very  rich  in  potash.  The  molasses 
contains  from  10  to  15  per  cent,  of  ash. 

The  composition  of  the  ash  varies  greatly  in  the  content  of 
potash  as  well  as  of  the  other  constituents.24  The  content  of 
potassium  carbonate  varies  from  22  to  55  per  cent,  and,  in  ad- 
dition to  this,  some  potassium  sulfate  and  chlorid  are  usually 
present. 

The  following  figures  give  the  composition  of  a  good  quality 
of  beet-molasses  ash : 

Per  cent. 

Potassium  carbonate 45-3° 

Sodium  carbonate 13 .86 

Potassium  chlorid 1 7.02 

Potassium  sulfate 8.00 

Silica,  lime,  alumina,  water,  phosphoric  acid,  and  unde- 
termined    15.82 

Thus,  in  100  parts  of  such  an  ash  over  three-quarters  are  pot- 
ash salts.  The  molasses  may  be  applied  directly  to  the  soil  or 
diluted  and  sprayed  over  the  fields. 

453.  Kinds  of  Potash  Fertilizers  Derived  from  Beet-Molasses. 
—The  by-products  from  the  factories  using  molasses  for  any 
purpose  contain  varying  amounts  of  potash,  and  this  renders  it 
uncertain  in  any  given  case,  without  a  special  analysis  to  deter- 
mine the  actual  quantity  of  potash  purchased.25  The  residue  from 
the  molasses  distillery  known  as  "Schlempekohle"  is  a  very  com- 
mon potash  product  in  the  German  markets.  The  residues  of  the 
still  are  evaporated  and  incinerated  to  a  carbonaceous  mass  suit- 
able for  transportation  and  application  to  the  soil.  In  this  prod- 
uct the  potash  is  chiefly  in  the  form  of  carbonate,  but  notable 
quantities  of  chlorid  and  sulfate  are  also  present.  The  potash 
mass  above  described  is  used  also  largely  for  the  manufacture 
of  commercial  potash  which  utilizes  the  greater  quantity  of  the 
chlorid  and  sulfate  present.  The  residue  is  dried  and  sold  also, 
as  a  potash  fertilizer,  but  contains  comparatively  very  little  pot- 

14  Horsin-De"on,  Traite1  de  la  Fabrication  du  Sucre,  2nd   Edition,  1900  : 
loot. 

"  Reitmair,  Wiener  landwirtschaftliche  Zeitung,  1905,  55  :  844. 


INSOLUBLE  POTASH  IN  PLANTS  535 

ash,  and  that  mostly  as  a  silicate.     It  is  known  as  "Schlempekoh- 
lenschlam." 

Another  product  is  made  by  the  evaporation  and  drying  of  the 
product,  so  as  to  avoid  calcination  and  preserve  the  nitrogenous 
constituents  intact.  Such  preparations  are  called  "Chilinit,"  a 
a  name  which  smacks  of  fraud,  since  the  nitrogen  therein  is  not  in 
the  form  of  saltpeter,  but  is  found  chiefly  as  amids  and  other  or- 
ganic combinations. 

454.  Residue  of  Wineries. — The  pomace  of  grapes  after  being 
pressed  or  fermented  for  wine  production  contains  considerable 
quantities  of  potash  as  crude  argol  or  acid  potassium  and  lime 
tartrate.     This  material  can  be  applied  directly  to  the  soil  or  first 
burned,  when  its  potash  will  be  secured  in  the  form  of  carbonate. 

The  use  of  the  winery  refuse  for  fertilizing  purposes  has  not 
assumed  any  commercial  importance  in  this  country. 

455.  Insoluble  Potash  in  Plants. — Berthelot  has  called  attention 
to  the  existence  of  plant  tissues  of  insoluble  alkaline  compounds.26 
Since,  in  the  estimation  of  potash,  we  often  extract  the  potash 
without  incineration,  it  is  evident  that  any  insoluble  material  of 
this  kind,  likewise,  of  lime,  or  other  alkaline  bodies,  will  not  be  in- 
cluded in  the  determination.     In  a  sample  of  hay  dried  at  110° 
it  was  found,  when  finely  ground  and  extracted  with  water,  that 
27.8  per  cent,  of  the  potash  was  soluble  and  72.2  per  cent,  insolu- 
ble. On  incineration  the  soluble  matter  was  found  to  contain  81.1 
per  cent,  of  organic  matter  and  18.9  per  cent,  of  ash.     The  or- 
ganic matter  contained: 

Per  cent. 

Carbon 49-4 

Hydrogen 6.65 

Nitrogen 2.20 

Oxygen  and  undetermined 41  -71 

The  ash  contained: 

Potash  (K2O) 5-95 

Lime  (CaO) 2.56 

Silica  (SiO2) 5-38 

Alumina,  phosphoric  acid  and  analogues 0.76 

Total 14-65 

Carbonic  acid,  undetermined  compounds  and  loss 8.65 

Total ; 23.3  of  ash 

or  mineral  matter  to  100  parts  of  organic  matter. 
™  Comptes  rendus,  1905,  141  :  793. 


536  AGRICULTURAL  ANALYSIS 

In  like  manner  the  insoluble  portion  was  examined  and  by  in- 
cineration yielded : 

Per  cent. 

Organic  matter 95-94 

Ash 4.06 

Or,  for  100  parts  organic  matter 4.21  of  ash. 

The  organic  matter  had  the  following  composition: 

Carbon 49-51 

Hydrogen 6.31 

Nitrogen 2.21 

Oxygen  and  undetermined 4*  -97 

The  ash  was  composed  of : 

Potash o.  13 

Lime 0.62 

Silica 2.31 

Alumina,  phosphoric  acid,  etc 0.41 

Carbonic  acid,  different  compounds  and  loss 0.74 

Total 4.21 

From  the  above  it  is  seen  that  the  soluble  part  contains  the 
greater  quantity  of  the  mineral  compounds,  not  only  as  was  to 
be  expected  of  potash,  but  also  of  lime  and  silica.  Nevertheless, 
there  exists  in  the  plant  a  notable  quantity  of  potash  entangled 
in  some  compound  insoluble  in  water,  amounting  to  about  two- 
tenths  of  the  total  potash  per  cent. 

456.  Forms  in  which  Potash  is  Found  in  Fertilizers. — The  chief 
natural  sources  of  potash  used  in  fertilizer  fabrication  are :  First, 
the  natural  mineral  deposits,  such  as  Stassfurt  salts ;  second,  the 
ash  derived  from  burning  terrestrial  plants  of  all  kinds;  third, 
organic  compounds,  such  as  desiccated  mineral  matters,  tobacco 
waste,  cottonseed  hulls,  etc. 

All  these  forms  of  potash  may  be  found  in  mixed  fertilizers. 
While  the  final  methods  of  analyses  are  the  same  in  all  cases  the 
preliminary  treatment  is  very  different,  being  adapted  to  the 
nature  of  the  sample.  For  analytical  purposes,  it  is  highly  im- 
portant that  the  potash  be  brought  into  a  soluble  mineral  form, 
and  that  any  organic  matters  which  the  sample  contains  be 
destroyed.  If  the  sample  be  already  of  a  mineral  nature,  it 


QUANTITY  OF  POTASH  REMOVED  BY  CROPS         537 

may  still  be  mixed  with  other  organic  matter  and  then  it  requires 
treatment  as  above,  for  it  is  not  safe  always  to  rely  solely  on  the 
solubility  of  the  potash  mineral,  and  the  solution,  moreover,  in 
such  cases,  is  likely  to  contain  organic  matter.  In  some  States, 
only  that  portion  of  the  potash  soluble  in  water  is  allowed  to  be 
considered  in  official  fertilizer  work.  In  these  cases  it  is  evident 
that  the  organic  matter  present  should  not  be  destroyed  in  the 
original  sample,  but  only  in  the  aqueous  solution.  Since,  how- 
ever, the  potash  occluded  in  organic  matter  becomes  constantly 
available  as  the  process  of  decay  goes  on,  it  is  not  advisable  to  ex- 
clude it  from  the  available  supply.  It  may  not  be  so  immediately 
available  as  when  in  a  soluble  mineral  state,  but  it  is  not  long 
before  it  becomes  valuable.  In  the  opinion  of  some  investigators 
phosphorus,  nitrogen,  and  potash  are  all  more  valuable  finally 
when  applied  to  the  soil  in  an  organic  form.  This  fact  is  not  irre- 
concilable'with  the  theory  already  advanced  that  all  mineral  com- 
pound bodies  are  probably  decomposed  before  they  enter  as  com- 
ponent parts  into  the  tissues  of  the  vegetable  organism. 

It  is  highly  probable,  therefore,  that  the  potash  existing  in 
organic  compounds,  finely  divided  and  easily  decomposed,  is  of 
equal,  if  not  greater  value  to  plant  life  than  that  already  in  a 
soluble  mineral  state.  For  analytical  purposes  the  organic  matter, 
when  present,  is  destroyed,  either  by  ignition  at  a  low  tempera- 
ture, or  by  moist  combustion  with  an  oxidizing  agent  before  the 
potash  is  precipitated.  For  agricultural  purposes  the  plant  food 
represented  by  the  potash  occluded  in  the  organic  substance  is 
held  with  some  degree  of  tenacity,  preventing  its  leaching  by 
heavy  rains,  and  permitting  its  gradual  release  as  required  by  the 
growing  plant. 

457.  Quantity  of  Potash  Removed  by  Crops. — The  quantity  of 
potash  removed  from  the  soil  annually  by  the  principal  crops  in 
the  United  States  is  equivalent  to  2,500,000  tons  of  muriate  of 
potash  or  1,250,000  tons  of  potash.27 

The  foregoing  discussion  of  the  sources  and  kinds  of  potash 
presented  to  the  analyst  is  sufficient  to  clearly  set  forth  the  ob- 
jects of  the  examination. 

17  Voorhees,  Journal  of  the  Franklin  Institute,  1905,  160  :  an. 


538  AGRICULTURAL   ANALYSIS 

METHODS  OF  ANALYSIS 


PREPARATION  OF  SAMPLE 

458.  Destruction  of  Organic  Matter  by  Direct  Ignition. — The 

simplest  and  most  direct  method  for  destroying  organic  matter  is 
by  direct  ignition.  The  incineration  may  be  conducted  in  the 
open  air  or  in  a  muffle  and  the  temperature  should  be  as  low  as 
possible.  In  no  case  should  a  low  red  heat  be  exceeded.  By 
reason  of  the  moderate  draft  produced  in  a  muffle  and  the  more 
even  heat  which  can  be  maintained  this  method  of  burning  is  to 
be  preferred.  With  the  exercise  of  due  care,  excellent  results 
can  be  obtained  in  an  open  dish  or  one  partly  closed  with  a  lid.  At 
first,  with  many  samples,  the  organic  matter  will  burn  of  its  own 
accord  after  it  is  once  ignited,  and  during  this  combustion  the 
lamp  should  be  withdrawn.  The  ignition  in  most  cases  should 
be  continued  in  a  platinum  dish  but  should  the  sample  contain  any 
reducible  metal  capable  of  injuring  the  platinum  a  porcelain  vessel 
should  be  used.  The  lamp  should  give  a  diffused  flame  to  avoid 
overheating  of  any  portions  of  the  dish  and  to  secure  more  uni- 
form combustion.  In  using  a  muffle  the  heat  employed  should 
be  only  great  enough  to  secure  combustion  and  the  draft  should 
be  so  regulated  as  to  avoid  loss  due  to  the  mechanical  deportation 
of  the  ash  particles. 

459.  Ignition  with  Sulfuric  Acid. — The    favorable     action    of 
sulfuric  acid  in  securing  a  perfect  incineration  may  also  be  util- 
ized in  the  preparation  of  samples  containing  organic  matter  for 
potash  determinations.     In  this  case  the  bases  which  by  direct 
ignition  would  be  secured  as  carbonates  are  obtained  as  sulfates. 
In  the  method  adopted  by  the  official  chemists  it  is  directed  to 
saturate  the  sample  with  sulfuric  acid  and  to  ignite  in  a  muffle 
until  all  organic  matter  is  destroyed.28     Afterwards,  when  cool 
the  ash  is  moistened  with  a  little  hydrochloric  acid  and  warmed, 
whereby  it  is  more  easily  detached  from  the  dish.     The  pot- 
ash is  then  determined  by  any  one  of  the   standard  methods. 
This  method  has  several   advantages   over  the  direct   ignition. 
Where  any  chlorids  of  the  alkalies  are  present  in  the  ash  there 

18  Bureau  of  Chemistry,  Bulletin  107,  1907  :  n. 


QUALITATIVE   DETECTION  539 

is  danger  of  loss  of  potash  from  volatilization.  This  is  avoided 
by  the  sulfate  process.  Moreover,  there  is  not  so  much  danger 
in  this  method  of  occluding  particles  of  carbon  in  the  ash. 

460.  The  Destruction  of  Organic  Matter  by  Moist  Combustion. 
— In  the  process  of  ignition  to  destroy  organic  matter  or  remove 
ammonium  salts  in  the  determination  of  potash,  there  are  often 
sources  of  error  which  may  cause  considerable  loss.     This  loss, 
as   has    already   been    mentioned,   may   arise   from   the   volatil- 
ization of  the  potash  salts  or  mechanically  from  spattering.     In 
order  to  avoid  these  causes  of  error  de  Roode  has  used  aqua  regia 
both  for  the  destruction  of  the  ammonium  salts  and  for  the  oxi- 
dation of  the  organic  matter  at  least  sufficiently  to  prevent  any 
subsequent  reduction  of  the  platinum  chlorid.29     The  method  con- 
sists in  boiling  a  sample  of  the  fertilizer,  or  an  aliquot  portion  of 
a  solution  thereof  with  aqua  regia.     The  proposed  method  has 
not  yet  had  a  sufficient  experimental  demonstration  to  warrant 
its  use,  but  analysts  may  find  it  profitable  to  compare  this  process 
with  the  standard  methods.     The  organic  matter  may  also  be 
destroyed  by  combustion  with  sulfuric  acid,  as  in  the  kjeldahl 
method   for  nitrogen.     The   residue,  however,   contains   ammo- 
nium sulfate  and  a  large  excess  of  sulfuric  acid,  and  for  both  rea- 
sons would  not  be  in  a  fit  condition  for  the  estimation  of  potash. 
It  is  suggested  that  the  organic  matter  may  also  be  destroyed 
by  boiling  with  strong  hydrochloric  acid,  to  which  from  time  to 
time,  small  quantities  of  sodium  chlorate  free  of  potash  is  added. 
Subsequently  the  solution  is  boiled  with  addition  of  a  little  nitric 
acid  and  the  ammonium  salts  thus  removed. 

461.  Qualitative   Detection. — To     detect     the     presence     of 
potash  in   a  mixture  the  aid  of  the   spectroscope  may  be  in- 
voked.    In  the  scale  of  the  spectrum  divided  into  170  parts,  on 
which  the  sodium  line  falls  at  50,  potassium  gives  three  faint 
rather  broad  bands,  two  red,  falling  at  17  and  27,  and  one  plum- 
colored  band,  near  the  extreme  right  of  the  spectrum,  at  153. 
Potassium,   however,   does   not  give  brilliant   and   well-marked 
spectral  bands,  such  as  are  afforded  by  its  associates,  rubidium, 
caesium,  sodium,  and  lithium.  A  convenient  qualitative  test  which 

29  Journal  of  the  American  Chemical  Society,  1895,  17  :  86. 


54O  AGRICULTURAL  ANALYSIS 

for  practical  purposes  will  be  quite  sufficient,  may  be  secured  by 
clipping  a  platinum  wire  loop  into  a  strong  acid  solution  of  the 
supposed  potash  compound,  and  viewing  through  a  piece  of  cobalt 
glass,  the  coloration  produced  thereby  when  held  in  the  flame  of 
a  bunsen.  The  red-purple  tint  thereby  produced  is  compared 
with  that  coming  from  a  pure  potash  salt  similarly  treated.  If 
a  fertilizer  sample  give  no  indication  of  potash  when  treated  as 
above  it  may  be  safely  concluded  that  it  does  not  contain  any 
weighable  quantity. 

For  the  estimation  of  the  percentage  of  potash  present  in  a 
given  sample  it  may  be  safely  assumed  that  all  of  value  in  agri- 
culture will  be  given  up  to  an  aqueous  or  slightly  acid  solution 
if  organic  matter  have  been  destroyed,  as  indicated  in  a  pre- 
vious paragraph.  In  the  case  of  minerals  insoluble  in  a  dilute 
acid,  the  potash  may  be  determined  by  some  one  of  the  processes 
given  in  the  first  volume. 

The  potash  having  been  obtained  in  an  aqueous  or  slightly 
acid  (hydrochloric)  solution,  it  may  be  determined  either  by 
precipitation  as  potassium  platino-chlorid  or  as  potassium  per- 
chlorate.  The  former  method  is  the  one  which  has  been  almost 
exclusively  used  by  analysts  in  the  past,  but  the  latter  one  is 
coming  into  prominence,  and  by  reason  of  the  greater  economy 
attending  its  practice  and  the  excellent  results  obtained  by  some 
analysts,  demands  a  generous  consideration. 

462.  The  Platinic  Chlorid  Method. — The  principle  of  this 
method  rests  on  the  great  insolubility  of  the  potassium  platino- 
chlorid  in  strong  alcohol  and  the  easy  solubility  of  some  of  its 
commonly  attending  salts ;  viz.,  sodium,  etc.,  in  the  same  re- 
agent. Before  the  precipitation  of  the  potash  it  is  customary  to 
remove  the  bases  of  the  earths,  sulfates,  etc.  Barium  chlorid 
and  hydroxid,  ammonium  oxalate  or  carbonate,  sulfuric  acid,  etc., 
are  used  in  conjunction  or  successively  to  effect  these  purposes 
in  the  manner  hereinafter  described.  The  filtrate  and  washings 
containing  the  potash  are  evaporated  to  dryness  and  gently  ignited 
to  expel  ammonium  salts  and  in  the  residue  taken  up  with  water 
and  acidulated  with  hydrochloric  acid,  the  potash  is  precipitated 


OFFICIAL    AGRICULTURAL     METHOD  54! 

-with  platinic  chlorid  solution.     The  best  methods  of  executing 
the  analysis  follow. 

463.  The  Official  Agricultural  Method. — This  method  is  based 
•on  the  processes  at  first  proposed  by  Lindo30  and  Gladding,31 
and  is  given  below  as  adapted  to  mixed  fertilizers  and  mineral 
potash  salts.32 

(1)  Preparation  of  reagents.  — (a)  Ammonium  chlorid  solu- 
tion.— Dissolve  ico  grams  of  ammonium  chlorid  in  500  cubic  cen- 
timeters of  water,  add  from  five  to  10  grams  of  pulverized  potas- 
sium-platinic  chlorid,  and  shake  at  intervals  for  six  or  eight  hours. 
The  mixture  is  allowed  to  settle  over  night  and  filtered,  and  the 
residue  is  ready  for  the  preparation  of  a  fresh  supply. 

(b)  Platinum  solution. — The  platinum  solution  used  contains 
one  gram  of  metallic  platinum  (2.1  grams  of  H2PtCl9)  in  every 
10  cubic  centimeters. 

(2)  Methods  of  making  solution. — (a)   With  potash  salts  and 
mixed  fertilizers. — Boil  10  grams  of  the  sample  with  300  cubic 
centimeters  of  water  30  minutes.    In  the  case  of  mixed  fertilizers 
add  to  the  hot  solution  a  slight  excess  of  ammonia  and  then  suffi- 
cient powdered   ammonium  oxalate  to   precipitate  all  the  lime 
present.     Cool,  dilute  to  '500  cubic  centimeters,  mix  and  pass 
through  a  dry  filter.     In  case  of  muriate  and  sulfate  of  potash, 
sulphate  of  potash  and  magnesia  and  kainit,  dissolve  and  dilute 
to  500  cubic  centimeters  without  the  addition  of  ammonium  and 
ammonium  oxalate. 

(b)  With  organic  compounds. — When  it  is  desired  to  determine 
the  total  amount  of  potash  in  organic  substances,  such  as  cotton- 
seed meal,  tobacco  stems,  etc.,  saturate  10  grams  with  strong  sul- 
furic  acid,  and  ignite  in  a  muffle  at  a  low  red  heat  to  destroy 
organic  matter.  Add  a  little  strong  hydrochloric  acid,  warm 
slightly  in  order  to  loosen  the  mass  from  the  dish,  and  proceed 
as  directed  under  (3)  (a)  below. 

(3)  Determination. — (a)   In  mixed  fertilizers. — Evaporate  50 
•cubic  centimeters  of  the  solution  made  according  to   (2),  cor- 

80  Chemical  News,  1881,  44  :  77,  86,  97,  129. 
51  Division  of  Chemistry,  Bulletin  7,  1885  :  38. 
"  Bureau  of  Chemistry,  Bulletin  107,  1907  :  n. 


542  AGRICULTURAL   ANALYSIS 

responding  to  one  gram  of  the  sample,  nearly  to  dryness,  add  one 
cubic  centimeter  of  dilute  sulfuric  acid  (i  to  i),  evaporate  to- 
dryness  and  ignite  to  whiteness.  As  all  the  potash  is  in  form  of 
sulfate,  no  loss  need  be  apprehended  by  volatilization  of  potash, 
and  a  full  red  heat  must  be  maintained  until  the  residue  is  per- 
fectly white.  Dissolve  the  residue  in  hot  water,  using  at  least 
20  cubic  centimeters  for  each  decigram  of  K2O,  add  a  few  drops 
of  hydrochloric  acid  and  platinum  solution  in  excess.  Evaporate 
on  a  water  bath  to  a  thick  paste  and  treat  the  residue  with  80 
per  cent,  alcohol,  specific  gravity  0.8645,  avoiding  the  absorp- 
tion of  ammonia.  Wash  the  precipitate  thoroughly  with  80  per 
cent,  alcohol  both  by  decantation  and  on  the  filter,  continuing  the 
washing  after  the  filtrate  is  colorless.  Wash  finally  with  10  cubic 
centimeters  of  the  ammonium  chlorid  solution  (i)  (a)  to  remove 
impurities  from  the  precipitate,  and  repeat  this  washing  five  or 
six  times.  Wash  again  thoroughly  with  80  per  cent,  alcohol, 
and  dry  the  precipitate  for  30  minutes  at  100°.  The  precipitate 
should  be  perfectly  soluble  in  water. 

(6)   Muriate  of  potash. — Dilute  25  cubic  centimeters  of  the 
solution,  prepared  according  to  (2)      (a),  with  25  cubic  centi- 
meters of  water,  acidify  with  a  few  drops  of  hydrochloric  acid, 
add  10  cubic  centimeters  of  platinum  solution  and  evaporate  to 
a  thick  paste.  Treat  the  residue  as  under  (3)  (a). 

(c)  Sulfate  of  potash,  sulfate  of  potash  and  magnesia,  and 
kainit. — Dilute  25  cubic  centimeters  of  the  solution,  prepared  ac- 
cording to  (2)  (a),  with  25  cubic  centimeters  of  water,  acidify 
with  a  few  drops  of  hydrochloric  acid  and  add  15  cubic  centime- 
ters of  platinum  solution.  Evaporate  the  mixture  and  proceed  as 
directed  under  (3)  (a),  except  that  25  cubic  centimeter  portions 
of  ammonium  chlorid  solution  should  be  used. 

(rf)  Water-soluble  potash  in  wood-ashes  and  cotton-hull  ashes. 
—Use  above  method  making  the  solution  according  to  (2)  (a),, 
and  pay  special  attention  to  the  last  sentence  (3)  (a). 

464.  Optional  Method. —  (i)  Preparation  of  reagent. — Platinum 
solution. — The  platinum  solution  used  is  the  same  as  that  de- 
scribed under  the  lindo-gladding  method. 

(2)  Method  of  making  solution. — The  solution  is  prepared  as 


POTASH    METHODS  543 

directed  under  the  lindo-gladding  method,  omitting  in  all  cases 
the  addition  of  ammonia  and  ammonium  oxalate. 

(3)  Determination. — Dilute  25  cubic  centimeters  of  the  solu- 
tion made  as  directed  under   (2),   (50  cubic  centimeters,  if  less 
than  10  per  cent,  of  potassium  oxid  be  present)   to   150  cubic 
-centimeters,  heat  to  100°,  and  add,  drop  by  drop,  with  constant 

stirring,  a  slight  excess  of  barium  chlorid  solution.  Without  fil- 
tering, add  in  the  same  manner  barium  hydrate  in  slight  excess. 
Filter  while  hot  and  wash  until  the  precipitate  is  free  from  chlo- 
rids.  Add  to  the  filtrate  one  cubic  centimeter  of  strong  ammo- 
nium hydrate,  and  then  a  saturated  solution  of  ammonium  car- 
bonate until  the  excess  of  barium  is  precipitated.  Heat  and  add, 
in  fine  powder,  0.5  gram  of  pure  oxalic  acid  or  0.75  gram  of 
.ammonium  oxalate.  Filter  and  wash  free  from  chlorids,  evap- 
orate the  filtrate  to  dryness  in  a  platinum  dish,  and  ignite  care- 
fully over  the  free  flame,  below  a  red  heat,  until  all  volatile  matter 
is  driven  off.  Digest  the  residue  with  hot  water,  filter  through  a 
small  fi'ter  and  dilute  the  filtrate,  if  necessary,  so  that  for  each 
•decigram  of  K2O  there  will  be  at  least  20  cubic  centimeters  of  a 
liquid.  Acidify  with  a  few  drops  of  hydrochloric  acid  and  add 
platinum  solution  in  excess.  Evaporate  on  a  water  bath  to  a 
thick  sirup  and  treat  the  residue  with  80  per  cent,  alcohol  (specif- 
ic gravity  0.8645).  Wash  the  precipitate  thoroughly  with  80  per 
cent,  alcohol  both  by  decantation  and  after  collecting  on  a  gooch 
or  other  form  of  filter.  Dry  for  30  minutes  at  100°  and  weigh. 
It  is  desirable,  if  there  be  an  appearance  of  foreign  matter  in 
the  double  salt,  that  it  should  be  washed  according  to  the  previous 
method  with  several  portions  of  the  ammonium  chlorid  solution 
of  10  cubic  centimeters  each. 

(4)  Factors. — For  the  conversion  of  potassium  platinochlorid 
to  KC1,  use  the  factor  0.3071 ;  to  K2SO4,  0.3589,  and  to  K2O, 
0.1941. 

465.  Potash  Methods  Recommended  by  the  Official  French  Com- 
mission.33— By  authority  of  law  the  President  of  the  French 
Republic  appointed  a  commission  for  the  purpose  of  prescribing 
official  methods  of  analyses  of  fertilizers.84  This  Commission  was 

3*  La  Sucrerie  indigene  et  coloniale,  1897,  49  :  645:  50  :  45- 

34  Grandeau,  Trait£  d' Analyse des  Matieres  agricoles,  3d  Edition,  1897, 


544  AGRICULTURAL  ANALYSIS 

composed  of  the  following  named  chemists:  Tisserand,  Vas- 
saliere,  Schloesing,  Prillieux,  Risler,  Aime  Girard,  Cornu,  Gran- 
deau,  Liebaut,  Joulie,  Mamelle,  Miintz  and  Marsais. 

Perchloric  Acid  Method. — The  preference  is  given  by  the 
French  Commission  to  this  method  which  is  conducted  accord- 
ing to  the  procedure  given  by  Schloesing,  which  is  substantially 
the  one  found  on  page  579.  The  method  varies  slightly  when 
used  with  the  different  salts  of  potash,  as,  for  instance,  the  sul- 
fates  and  the  chlorids.  There  is  also  a  very  slight  difference  in  the 
manipulation  where  the  potash  is  contained  in  a  complex  or  mixed 
fertilizer.  The  above  differences  refer,  however,  solely  to  the  pre- 
liminary treatment  and  to  the  elimination  of  the  potash  from  its 
principal  compounds. 

Platinum  Chlorid  Method. — The  French  commission  has  also 
recommended  the  platinum  method  for  the  determination  of  pot- 
ash in  the  form  of  double  chlorids  of  potash  and  platinum.  The 
method  described  does  not  differ  in  any  essential  points  from  that 
already  given.  Where  it  is  advisable  to  estimate  the  soda  also, 
the  total  chlorin  is  determined  in  the  mixed  chlorids,  the  potash1 
estimated  by  the  platinum  method,  the  chlorin  necessary  to  com- 
bine with  it  deducted  from  the  total  chlorin  and  the  residual 
chlorin  calculated  to  chlorid  of  soda. 

Method  of  Corenwindcr  and  Contamine. — The  French  commis- 
sion has  recommended  also  as  one  of  the  alternative  methods  the 
determination  of  potassium  in  salts  and  in  refined  potash  com- 
pounds according  to  the  variations  of  Corenwinder  and  Con- 
tamine, in  which  there  is  introduced  into  the  process  as  a  reagent, 
sodium  formate.  This  method  is  regarded  by  the  Commission 
as  exact  as  that  in  which  the  perchlorate  is  used.  In  this  process 
25  grams  of  the  salt  to  be  examined  is  ignited  in  case  it  con- 
tains any  organic  matter  or  salts  of  ammonia,  which  must  pre- 
viously be  destroyed  or  eliminated.  After  cooling,  the  melt  is 
dissolved  and  the  volume  brought  to  one  liter  and  the  solution 
filtered.  An  aliquot  part  of  the  filtrate,  conveniently  20  cubic 
centimeters,  corresponding  to  five  decigrams  of  the  original  mate- 
rial, is  acidulated  with  hydrochloric  acid,  evaporated  to  dryness, 
and  the  saline  residue  weighed  for  the  purpose  of  determining; 


POTASH    METHODS  545 

what  quantity  of  chlorid  of  platinum  should  be  added  in  order  that 
it  will  be  in  slight  excess.  The  quantity  of  the  platinum  reagent 
used  is  calculated  in  such  a  way  that  it  is  sufficient  to  saturate 
the  whole  quantity  of  the  salts  present,  which  are  for  this  purpose 
calculated  as  if  they  were  the  chlorid  of  sodium.  The  chlorid  of 
platinum  employed  should  contain  in  100  cubic  centimeters  17 
grams  of  platinum.  Each  cubic  centimeter  of  the  solution  is  suffi- 
cient for  each  decigram  of  the  weight  of  the  saline  residue  obtain- 
ed as  above.  After  adding  the  platinum  salts  the  mixture  is  placed 
in  a  capsule  and  evaporated  with  precautions  to  prevent  the  plati- 
num salt  from  being  heated  beyond  a  temperature  of  100°.  Above 
this  temperature  the  salts  may  form  a  little  of  the  subchlorid  of 
platinum  which  is  insoluble  in  alcohol.  After  cooling,  the  mass 
is  digested  for  several  hours  with  15  cubic  centimeters  of  95  per 
cent,  alcohol,  the  capsule  being  placed  under  a  small  cover.  Dur- 
ing this  time  it  is  stirred  from  time  to  time  with  a  glass  rod  and 
the  supernatant  liquid  is  poured  into  a  small  filter  and  the  salt 
washed  with  alcohol  until  the  filtrate  becomes  colorless.  There  is 
thus  obtained  as  an  insoluble  residue  a  mixture  of  chloro-platinate 
of  potassium  with  various  quantities  of  soda,  silicates  and  oxids 
of  iron  which  may  have  been  present  in  the  original  sample. 
By  means  of  boiling  water  the  mass  remaining  in  the  capsules 
is  dissolved  and  poured  upon  the  filter  and  the  washing  of  the 
capsule  is  continued  with  boiling  water  until  all  of  the  chloro- 
platinate  is  dissolved,  which  is  easily  determined  by  the  alcohol 
wash  becoming  colorless.  The  solution  of  chloro-platinate  is  re- 
ceived in  a  well  glazed  dish,  containing  no  cracks,  and  is  heated 
upon  a  sand  bath  to  boiling  and  there  is  added  to  it  in  very  small 
proportions  some  formate  of  soda  dissolved  in  water.  The  cap- 
sules having  been  taken  from  the  bath  to  avoid  mechanical  loss, 
formate  of  soda  is  added  until  the  mixture  is  completely  decolor- 
ized. Instead  of  doing  this  in  an  ordinary'  dish,  an  open  flask  or 
beaker  may  be  employed.  By  this  process  the  platinum  present 
in  the  mixture  is  precipitated  as  a  black  powder,  and  in  order  to 
aggregate  it,  the  mixture  is  evaporated  to  about  one-half  its  vol- 
ume and  brought  upon  a  small  filter,  bringing  the  platinum  in  by 
means  of  cold  water  slightly  acidulated.  When  all  the  platinum 
18 


546  AGRICULTURAL  ANALYSIS 

is  brought  together  upon  the  filter  •  the  washing  is  finished  by 
means  of  boiling  water.  Sometimes  the  finely  divided  platinum 
passes  through  the  filter,  which  is  easily  detected  by  a  gray  metal- 
lic tint  which  the  filtered  liquid  assumes.  In  this  case  it  is  neces- 
sary to  allow  it  to  settle  for  one  or  two  days,  decant  the  color- 
less supernatant  liquid  and  add  the  deposited  matter  to  the  filter 
by  means  of  cold  water.  Finally,  the  filter  is  dried  and  ignited 
and  there  is  obtained  in  this  way  the  weight  of  metallic  platinum 
corresponding  to  that  of  potassium  in  the  original  sample,  since 
100  parts  of  platinum  are  equivalent  to  47.57  of  potash. 

466.  Method  of  Potash  Determination   of  the  Union  of  Ger- 
man  Fertilizer   Manufacturers. — The   method   of   potash    deter- 
mination employed  by  the  Union  of  German  Chemists  is  the  same 
as  that  recommended  by  the  Potash  Syndicate  of  Stassfurt,  with 
only  slight  modifications.35     The  German  manufacturers,  how- 
ever, use  the  atomic  weight  of  platinum,  194.8,  instead  of  197.2,  as 
employed  by  the  syndicate.     The  factors,  therefore,  for  conver- 
sion in  the  two  cases  are  slightly  different. 

467.  Methods  Used  at  the  Halle  Station. — (i)  In  Kainits  and 
other  Mineral  Salts  of  Potash.30 — Five  grams  of  the  prepared 
sample  are  boiled  for  half  an  hour  in  a  half  liter  flask  with  from 
20  to  30  cubic  centimeters  of  concentrated  hydrochloric  acid  and 
100  cubic  centimeters  of  water,  and  afterwards  as  much  water 
added  as  is  necessary  to  fill  the  flask  about  three-quarters  full, 
and  the  sulfuric  acid  is  then  precipitated  with  barium  chlorid.  To 
avoid  an  excess  of  barium  chlorid  the  solution  used  is  of  known 
strength  and  is  added  first  in  such  quantity  as  would  precipitate 
the  sulfuric  acid  from  a  kainit  of  low  sulfuric  acid  content.    The 
mixture  is  then  boiled,  allowed  to  settle  and  tried  with  a  drop- 
ping tube  containing  barium  chlorid.     If  a  further  precipitate 
appear,  a  few  drops  more  of  barium  chlorid  solution  are  added, 
again  boiled  and  allowed  to  settle.    This  is  continued  until  barium 
chlorid  gives  no  precipitation.     After  the  barium  chlorid  gives 
no  more  precipitate  a  drop  of  dilute  sulfuric  acid  is  added  to  test 

M  Methoden  zur  Untersuchung  der  Kunstdiingemittel,  1903  :  21. 
34  Bieler  undSchneidewind,  Die  agricultur-chemische  Versuchsstation, 
Halle  a/S,  1892  :  76. 


METHODS   USED   AT   THE    HALLE   STATION  547 

for  excess  of  barium.  The  operation  is  continued  with  the  sul- 
furic  acid  until  it  no  longer  gives  a  precipitate  of  barium  sulfate. 
By  the  alternate  use  of  the  barium  chlorid  and  sulfuric  acid  the 
exact  neutral  point  can  soon  be  secured.  When  this  point  is 
reached  the  liquid  is  allowed  to  cool,  the  flask  is  filled  to  the 
mark,  its  contents  filtered,  and  of  the  filtrate  50  cubic  centimeters, 
equal  to  half  a  gram  of  the  substance,  removed  for  further  esti- 
mation. 

This  quantity  is  evaporated  on  a  water  bath  to  a  sirupy  con- 
sistence in  a  porcelain  dish  with  10  cubic  centimeters  of  platinic 
chlorid.  The  platinic  chlorid  solution  should  contain  one  gram 
of  platinum  in  each  10  cubic  centimeters.  The  residue  is  treated 
with  80  per  cent,  alcohol  and,  with  stirring,  allowed  to  stand 
for  an  hour.  The  precipitate  is  then  collected  on  a  gooch,  either 
of  platinum  or  porcelain,  washed  about  eight  times  with  80  per 
cent,  alcohol,  and  the  potassium  platinochlorid  dried  for  two  hours 
at  100°.  After  weighing,  the  precipitate  is  dissolved  in  hot 
water  and  the  residue  washed,  first  with  hot  water  and  then  with 
alcohol.  The  crucible  with  the  asbestos  felt  is  dried  at  100°  and 
weighed.  Any  impurities  which  the  double  salt  may. have  carried 
down  with  it  are  left  on  the  filter  and  the  weight  of  the  original 
precipitate  can  thus  be  corrected.  The  weight  of  potassium  pla- 
tinochlorid is  multiplied  by  0.1927  and  the  product  corresponds 
to  the  weight  of  K2O  in  the  sample. 

(2)  Estimation  of  Potash  in  Guanos  and  Other  Fertilisers  con- 
taining Organic  Substances. — Ten  grams  of  the  substances  are 
carefully  incinerated  at  a  low  temperature  in  a  platinum  dish. 
After  ignition  the  contents  of  the  dish  are  placed  in  a  half  liter 
flask  and  boiled  for  an  hour  with  hydrochloric  acid  and  a  few 
drops  of  nitric  acid.  The  sulfuric  acid  can  then  be  precipitated 
directly  with  barium  chlorid,  or  better,  allow  the  flask  to  cool, 
fill  to  the  mark,  filter  and  treat  an  aliquot  part  of  the  filtrate  with 
barium  chlorid  as  described  above.  The  filtrate  from  the  sep- 
arated sulfate  of  barium  is  neutralized  with  ammonia  and  all  the 
bases,  with  the  exception  of  magnesia  and  the  alkalies,  precipi- 
tated with  ammonium  carbonate,  and  the  mixture  boiled,  filled  to 
the  mark  and  filtered.  From  100  to  200  cubic  centimeters  of  this 


548  AGRICULTURAL  ANALYSIS 

filtrate  are  evaporated  in  a  platinum  dish.  After  evaporation  the 
ammonium  salts  are  driven  off  by  careful  ignition,  the  residue 
taken  up  with  hot  water  and  filtered  through  as  small  a  filter  as 
possible  into  a  porcelain  dish,  the  magnesia  remaining  in  the 
precipitate.  The  filtrate  is  acidified  with  a  few  drops  of  hydro- 
chloric acid,  10  cubic  centimeters  of  platinic  chlorid  added  and 
the  further  determination  conducted  as  with  kainit. 

468.  Dutch  Method. — The  process  used  at  the  Royal  Agri- 
cultural Station  of  Holland  is  almost  identical  with  that  em- 
ployed at  Halle.37 

A.  Method  for  Stassfurt  and  other  Potash  Salts. — The  neces- 
sary reagents  are: 

1.  A  dilute  solution  of  barium  chlorid. 

2.  A  solution  of  platinic  chlorid  containing  one  gram  of  plati- 
num in  10  cubic  centimeters.     It  must  be  wholly  free  from  plati- 
nous  chlorid  and  nitric  acid,  and  partially  freed  from  an  excess 
of  hydrochloric  acid  by  repeated  evaporations  with  water. 

3.  Alcohol  of  80  per  cent,  strength  by  volume. 

The  methods  of  bringing  the  potash  into  solution  and  of  pre- 
cipitating the  sulfuric  acid  are  the  same  as  for  the  Halle  pro- 
cess described  above. 

To  50  cubic  centimeters  of  the  solution  add  20  cubic  centime- 
ters of  the  platinum  solution  and  evaporate  the  mixture  nearly 
to  dryness.  Add  a  sufficient  quantity  of  80  per  cent,  alcohol 
and  stir  for  some  time.  Allow  to  stand  and  then  filter  through 
a  gooch  dried  at  120°.  Finally  wash  with  80  per  cent,  alcohol 
dry  at  120°,  and  weigh. 

B.  Method  for  Potash-Superphosphate  and  other  mixed  Fer- 
tilizers.— The  reagents  necessary  are  the  same  as  under  A,  and, 
in  addition,  a  saturated  solution  of  barium  hydrate  and  a  solu- 
tion of  ammonium  carbonate  mixed  with  ammonia. 

Boil  20  grams  of  the  substance  with  water  for  half  an  hour, 
cool,  make  up  to  half  a  liter  and  filter.  Boil  50  cubic  centimeters 
of  the  filtrate,  and  add  barium  chlorid  till  no  more  precipitate 
forms.  Mix  with  baryta  water  to  strong  alkaline  reaction,  cool, 
make  up  to  100  cubic  centimeters  and  filter.  Raise  50  cubic  cen- 
"  Methoden  von  Onderzoek  aan  de  Rijkslandbouwproefstations,  1894  :  6. 


SWEDISH   METHODS  549 

timeters  of  the  filtrate  to  the  boiling  temperature  and  add  am- 
monium carbonate  solution  till  no  more  precipitate  forms.  Cool 
make  up  to  100  cubic  centimeters  and  filter.  Transfer  50  cubic 
centimeters  of  the  filtrate  to  a  platinum  dish,  evaporate  and  heat 
the  residue,  avoiding  too  high  a  temperature,  till  the  ammonia 
salts  are  expelled.  Dissolve  the  residue  in  water,  filter,  and  treat 
the  filtrate  as  described  under  A. 

469.  Swedish  Methods. — The  Swedish  chemists  determine  the 
potash  in  mineral  salts  by  the  platinum  chlorid  process,  but  with 
certain  variations  from  the  processes  already  given.  The  manipu- 
lation is  conducted  as  follows  :38 

Pour  about  300  cubic  centimeters  of  hot  water  over  one  gram 
of  the  sample  to  be  examined  in  a  beaker,  and  filter  after  com- 
plete solution ;  add  one  cubic  centimeter  of  hydrochloric  acid,  heat 
nearly  to  boiling,  add  dilute  barium  chlorid  solution  from  a  pipette 
or  burette  in  a  very  fine  stream,  stirring  slowly  and  carefully, 
till  all  sulfuric  acid  is  completely  precipitated,  and  only  a  trace 
of  the  precipitant  is  in  excess.  If  the  precipitation  be  conducted 
in  the  way  given,  the  barium  sulfate  will  come  down  in  crystal- 
line condition,  and  settle  rapidly  within  a  few  minutes,  and  al- 
most immediately  after  the  precipitation  is  finished  may  be  fil- 
tered clear.  Bring  the  filtrate  and  washings  from  the  barium 
sulfate  into  a  liter  flask;  fill  this  to  the  mark,  take  out  50  cubic 
centimeters  with  a  pipette,  evaporate  the  greater  portion  on  a 
water  bath  in  a  porcelain  dish,  transfer  the  residue  by  means  of 
ammonia-free  water  to  a  beaker  of  50  cubic  centimeters  capacity, 
add  10  cubic  centimeters  of  platinic  chlorid  solution,  stir  well  with 
a  glass  rod,  evaporate  on  a  water  bath  to  a  sirupy  condition,  allow 
to  cool,  and  if  the  residue  be  too  dry,  add  a  few  drops  of  water  to 
allow  the  sodium  platinochlorid  to  take  up  crystal  water  with 
certainty,  stir  well,  add  alcohol  after  a  few  minutes,  mix  care- 
fully, leave  the  mixture  standing  for  a  while  in  the  beaker  cov- 
ered with  a  watch-glass,  stirring  occasionally;  finally,  decant  the 
solution,  which  must  be  of  a  dark  yellow  color,  through  a  very 
small  filter,  wash  the  precipitate  in  the  beaker  repeatedly  with 
small  quantities  of  alcohol  and  decant;  then  transfer  the  precipi- 
M  Official  Swedish  Methods,  translated  for  the  Author  by  F.  W.  Woll. 


550  AGRICULTURAL  ANALYSIS 

tate  to  the  filter,  wash  with  alcohol,  dry  the  filter  and  the  precipi- 
tate at  a  gentle  heat  till  all  alcohol  has  evaporated,  carefully 
transfer  the  contents  of  the  filter  to  a  watch  glass  placed  on  white 
glazed  paper;  dissolve  the  potassium  platinochlorid  still  remain- 
ing on  the  filter  in  small  quantities  of  boiling  water,  evaporate 
the  filtrate  on  a  water  bath  in  an  accurately  weighed  platinum 
dish  to  dryness  and  transfer  to  the  same  the  main  portion  of  the 
chlorid  from  the  watch-glass.  In  order  to  obtain  the  salt  free  of 
the  corresponding  combinations  of  sodium,  barium,  calcium,  and 
magnesium,  which  salts,  although  soluble  in  alcohol,  may  make 
the  salt  impure,  before  weighing  treat  the  precipitate  twice  with 
small  quantities  of  cold  water,  which  will  dissolve  these  im- 
purities ;  evaporate  the  solution  after  addition  of  one  cubic  cen- 
timeter of  platinic  chlorid  nearly  to  dryness  on  a  water  bath, 
treat  the  residue  in  the  same  way  as  given  before,  add  the  small 
quantity  of  potassium  platinochlorid  which  is  hereby  obtained 
together  with  the  main  portion  to  the  platinum  dish,  dry  at  130°, 
and  weigh.  Only  after  having  been  treated  in  this  way  may  the 
precipitated  potassium  platinochlorid  be  considered  absolutely 
pure.  The  Stassfurt  salts  contain  magnesia,  often  in  large  quan- 
tities, and  as  a  consequence  the  potassium  platinochlorid  precipi- 
tated directly  is  likely  to  be  contaminated  therewith. 

470.  Methods  for  the  Analysis  of  Carnallit,  Kainit,  Sylvinit, 
and  Bergkieserit. — The  chemists  of  the  German  Potash  Syndi- 
cate use  the  following  methods  in  the  analysis  of  the  raw  products 
mentioned  above.39 

1 I )  Preparation  of  the  Sample. — It  is  advisable  to  take  from  a 
large,  well  mixed  mass  at  least  half  a  kilogram  for  the  analytical 
sample,  and  this  should  be  ground  to  a  fine  powder  in  a  mill  or 
mortar. 

(2)  Estimation  of  the  Potash  by  the  Precipitation  Method. — In 
a  half  liter  flask  are  placed  35.71   grams  of  kainit,  hartsalz  or 
sylvinit,  or  30.56  grams  of  carnallit  or  bergkieserit,  which  are 
boiled  with  350  cubic  centimeters  of  water  after  the  addition  of 
10  cubic  centimeters   of  hydrochloric   acid.   After  cooling,   the 

39  Division  of  Chemistry,  Bulletin  35,  1892  :  63. 

Methods  of  Analyses  of  Potash  Salts,  Published  by  the  Kalisyndikat, 
Leopoldshall-Stassfurt,  1906. 


ANALYSIS  OF  CARNALUT,  KAINIT,  ETC.  551 

flask  is  filled  to  the  mark  with  water,  well  shaken,  and  its  con- 
tents filtered.  Fifty  cubic  centimeters  of  the  filtrate  are  treated  in 
a  200  cubic  centimeter  flask  with  a  solution  of  barium  chlorid, 
the  flask  filled  to  the  mark,  well  shaken,  and  its  contents  filtered. 
Twenty  cubic  centimeters  of  the  filtrate,  corresponding  to  0.3571 
or  0.3056  gram  of  the  substance,  as  the  case  may  be,  are  treated 
with  five  cubic  centimeters  of  platinic  chlorid  solution  and  the 
potassium  estimated  according  to  the  usual  methods.  When  the 
perchloric  acid  method  is  employed,  13.455  grams  of  the  carnallit 
or  bergkieserit,  or  15.7225  grams  of  kainit,  sylvinit  or  hartsalz 
are  dissolved  in  a  500  cubic  centimeter  flask  and  treated  directly 
with  barium  chlorid.  Twenty  cubic  centimeters  of  the  filtrate,  t 
equal  to  0.5382  or  0.6289  gram  of  the  sample,  as  the  case  may 
be,  are  then  treated  with  perchloric  acid,  as  described  further 
along. 

(3)  Estimation  of  Potash  (K2O)  in  Raw  Potash  Salts. — (a) 
For  the  determination  of  potash  alone  in  carnallit,  kainit,  and  syl- 
vinit 100  grams  of  the  well-mixed  sample  are  put  into  a  grad- 
uated flask  holding  one  liter  and  dissolved  by  boiling  with  half 
a  liter  of  water,  acidulated  with  10  cubic  centimeters  of  hydro- 
chloric. The  purpose  of  adding  hydrochloric  acid  is  to  bring 
any  polyhalit  that  might  be  present  in  the  salts  into  solution  and 
which  it  is  difficult  to  dissolve  in  pure  water.  After  dissolving 
and  cooling,  the  flask  is  filled  up  to  the  mark.  The  solution, 
after  mixing,  is  filtered  through  a  dry  filter  and  100  cubic  centi- 
meters of  the  filtrate,  corresponding  to  10  grams  substance,  are 
put  into  a  half  liter  flask  by  means  of  a  pipette.  After  the  addi- 
tion of  200-300  cubic  centimeters  of  water  the  solution  is  heated 
to  boiling  and  the  sulfuric  acid  accurately  precipitated  with  nor- 
mal barium  chlorid  solution,  containing  104  grams  of  the  dry 
salt  in  one  liter.  The  volume  of  the  precipitate  is  calculated  from 
the  amount  of  barium  solution  used  and  from  the  specific  gravity 
of  the  barium  sulfate.  After  cooling,  the  flask  is  filled  up  with 
water  as  far  above  the  mark  as  equals  the  volume  of  the  calcu- 
lated barium  precipitate,  and,  after  thorough  mixing,  the  solu- 
tion is  filtered  again  through  a  dry  filter.  Fifty  cubic  centi- 
meters of  this  filtrate,  corresponding  to  one  gram  substance,  are 


552  AGRICULTURAL  ANALYSIS 

evaporated  upon  the  water  bath  with  a  sufficient  amount  of  pla- 
tinic  chlorid.  The  residue  of  potassium  platinochlorid  is  washed 
with  90  per  cent,  alcohol,  dried  at  120°,  and  weighed. 

(6)  If  it  be  desired  to  determine  separately  the  quantity  of 
potash  present  in  the  form  of  sulfate  and  in  the  form  of  chlorid, 
as,  for  example,  in  kainit  and  in  sulfate  of  potash,  or  if  it  is  to  be 
determined  whether  potassium  sulfate  is  in  combination  with  a 
proportionate  amount  of  magnesium  chlorid,  as  in  kainit,  or  in 
combination  with  magnesium  sulfate  alone,  as  in  schonit,  it  then 
becomes  necessary  to  determine  besides  potash  the  percentages 
of  chlorin,  sulfuric  acid,  lime,  magnesia,  the  total  alkalies,  water, 
tand  the  residue  insoluble  in  water.  For  this  purpose  100 
grams  of  the  sample  are  dissolved,  the  solution  is  filtered,  the 
filter  washed,  and  the  filtrate  made  up  to  one  liter ;  a  part  of  the 
liquid  is  taken  for  the  determination  of  sulfuric  acid,  by  precipi- 
tating with  barium  chlorid,  and  another  part  for  the  determina- 
tion of  lime  and  magnesia.  For  the  determination  of  the  alkali 
chlorids,  100  cubic  centimeters  of  the  solution,  corresponding  to 
10  grams  substance,  are  acidulated  with  hydrochloric,  and,  after 
heating  to  boiling,  the  sulfuric  acid  is  completely  precipitated 
with  barium  chlorid,  with  the  precaution  of  using  not  more  of 
the  barium  solution  than  is  necessary  for  the  complete  precipita- 
tion. Fifty  cubic  centimeters  of  the  filtered  solution,  correspond- 
ing to  one  gram  substance,  are  evaporated  to  dryness  in  order  to 
drive  off  the  hydrochloric  acid.  Magnesium  chlorid  is  decom- 
posed by  igniting  with  oxalic  acid.  After  ignition,  the  residue 
is  moistened  with  a  little  ammonium  carbonate  for  the  purpose 
of  converting  the  calcium  oxid  that  may  have  been  formed  into 
calcium  carbonate.  The  alkali  chlorids,  which  are  entirely  free 
of  lime  and  magnesia,  are  weighed,  and  potassium  chlorid  is  de- 
termined by  means  of  platinic  chlorid  or  perchloric  acid.  The 
amount  of  sodium  chlorid  is  obtained  by  deducting  potassium 
chlorid  from  the  mixed  chlorids. 

Estimation  of  Water. — For  the  water  determination  five  grams 
of  the  sample  are  ignited  and  the  loss  of  weight  is  determined. 
The  ignited  mass  is  dissolved  in  water,  and  for  the  purpose  of 
determining  the  quantity  of  magnesium  chlorid  that  may  have 


ANALYSIS  OF  CARNALUT,  KAINIT,  ETC.  553 

been  decomposed  by  the  ignition,  the  percentage  of  chlorin  is 
determined  by  titration.  The  difference  in  the  contents  of  chlorin 
before  and  after  ignition  is  subtracted  from  the  loss  in  weight, 
after  allowance  has  been  made  for  the  absorption  of  oxygen  and 
for  the  loss  of  hydrogen.  The  rest  is  water.  Or,  in  order  to 
avoid  the  loss  of  chlorin,  the  sample  is  covered  by  a  known 
quantity  of  freshly  ignited  burnt  lime  or  lead  oxid  to  absorb  the 
chlorin  from  the  magnesium  chlorid. 

Calculation  of  Composition. — The  results  obtained  are  calcu- 
lated in  the  following  manner:  From  the  total  amount  of  the 
sulfuric  acid  found,  that  portion  is  deducted  which  is  combined 
with  calcium  as  calcium  sulfate ;  the  rest  of  the  sulfuric  acid  is 
divided  into  two  equal  parts  for  the  purpose  of  calculating  the 
contents  of  potassium  sulfate  and  magnesium  sulfate,  according 
to  the  molecular  proportion  in  which  these  salts  are  present  in 
kainit  and  in  schonit.  If  there  be  an  excess  of  potash  left  un- 
combined  with  sulfuric  acid,  then  it  is  in  the  form  of  potassium 
chlorid ;  likewise,  the  amount  of  magnesia,  uncombined  with  sul- 
furic acid,  is  to  be  reckoned  as  magnesium  chlorid.  The  result 
of  this  calculation  will  tell  how  much  potash  is  in  the  form  of 
kainit  (K,SO4,  MgSO4,  MgCl,,  with  6H2O)  and  how  much  of 
it  is  in  the  form  of  schonit  (K2SO4,  MgSO4,  with  6H2O)  and 
how  much  in  the  form  of  potassium  chlorid.  The  sodium  is  reck- 
oned as  sodium  chlorid. 

In  the  case  of  hartsalz,  the  water  content  of  which  is  only 
about  one-third  of  that  in  kainit,  the  potassium  is  calculated  as 
chlorid.  When  longbeinit  (K2SO4,2MgSO4)  is  present  with 
kainit,  the  magnesia  and  lime  present  are  credited  as  sulfates, 
the  excess  of  sulfuric  acid  remaining  being  then  reckoned  as 
a  potassium  salt.  Should  a  complete  examination  and  identifica- 
tion of  the  various  minerals  present  in  a  more  complicated  mix- 
ture of  the  crude  salts  be  required,  this  cannot  be  performed  from 
calculations  founded  simply  upon  a  quantitative  chemical  analysis 
of  the  various  constituents.  In  such  a  case  for  example  the  mag- 
nesium chlorid  soluble  in  alcohol  should  be  determined,  as  from 
this  the  proportion  of  carnallit  may  be  reckoned.  Further  aid 


554  AGRICULTURAL  ANALYSIS 

will  be  obtained  in  separating  the  minerals  with  bromoform  ac- 
cording to  their  varying  specific  gravities. 

Calculations  of  the  salts  present  in  carnallit  and  bergkieserit 
are  obtained  in  the  following  manner:  The  lime  found  is  reck- 
oned as  sulfate,  and  the  excess  of  sulfuric  acid,  after  satisfying 
the  lime,  is  then  credited  to  magnesia.  The  remaining  magnesium 
is  stated  as  magnesium  chlorid. 

(c)  In  calculating  the  contents  of  potash,  of  potassium  chlorid, 
and  of  potassium  sulfate  from  the  weighed  potassium  platino- 
chlorid,  the  factors  0.1928,  0.3056,  and  0.3566  are  used,  assuming 
that  the  atomic  weight  of  platinum  is  197.18. 

(•d)  The  two  methods  which  have  been  described  under  a  and 
b,  and  which  are  in  common  use  in  the  Stassfurt  potash  indus- 
try, i.  e.,  the  so-called  precipitation  method,  and  the  oxalic  acid 
method,  give  almost  identical  results.  The  first  method,  how- 
ever, deserves  preference  on  account  of  greater  simplicity  in 
cases  where  potash  alone  is  to  be  determined.  Finkener's  method 
likewise  gives  results  which  agree  well  with  the  results  obtained 
by  the  customary  methods.  It  consists  in  evaporating  the  salt 
solution  with  a  sufficient  quantity  of  platinic  chlorid  without  pre- 
viously removing  the  sulfuric  acid,  reducing  the  potassium  platino- 
chlorid,  and  weighing  the  metallic  platinum. 

The  following  are  the  results  of  comparative  analyses : 

1.  After  the  precipitation  method 22.02  per  cent.  KC1 

2.  After  the  oxalic  acid  method 22.03  per  cent.  KC1 

3.  After  Finkner's  method 22.01  per  cent.  KC1 

In  another  sample  of  carnallit  the  following  results  were  ob- 
tained : 

1.  After  the  precipitation  method 17.88  per  cent.  KC1 

2.  After  the  oxalic  acid  method 17.88  per  cent.  KC1 

In  a  third  sample  of  carnallit  the  content  of  potassium  chlorid 
was  as  follows : 

1.  After  the  precipitation  method 18.44  per  cent. 

2.  After  the  oxalic  acid  method 18.38  per  cent. 

The  German  chemists  object  to  precipitating  the  sulfuric  acid 
and  alkaline  earths  with  barium  oxid  and  ammonium  carbonate, 
and  afterwards  the  potash  with  platinic  chlorid.  The  results  ob- 


METHODS  FOR  CONCENTRATED  POTASH  SALTS  555 

tained  with  this  method  are,  according"  to  them,  very  inaccurate, 
and  always  too  low.  This  is  explained  by  the  fact  that  it  is  im- 
possible to  precipitate  sulfuric  acid  without  the  same  time  pre- 
cipitating some  of  the  potash,  unless  it  be  in  an  acid  solution. 

A  separation  of  the  alkaline  earths,  if  potash  alone  is  to  be 
determined,  is  superfluous,  for  the  reason  that  calcium  and  mag- 
nesium platinochlorid  are  soluble  in  90  per  cent,  alcohol,  even 
with  more  facility  than  sodium  platinochlorid. 

471.  Methods  for  Concentrated  Potash  Salts. — In  the  pre- 
ceding paragraphs  have  been  given  the  methods  used  by  the 
Stassfurt  syndicate  for  the  estimation  of  potash  in  the  raw  salts 
as  they  come  from  the  mines.  Following  are  the  methods  used 
by  the  same  syndicate  for  the  concentrated  approximately  pure 
compounds  and  the  other  salts  which  accompany  them.40 

Potassium  Chlorid. — The  following  process  is  used  for  the  esti- 
mation of  potassium  and  other  constituents  of  the  high  grade 
chlorids  of  commerce.  In  a  half  liter  flask  are  placed  7.6401 
grams  of  the  finely  powdered  sample,  which  is  dissolved  and 
made  up  to  the  mark.  With  salts  which  contain  more  than  half 
a  per  cent,  of  sulfuric  acid  the  preliminary  conversion  of  the  sul- 
fates  into  the  corresponding  chlorin  compounds,  by  precipitation 
with  barium  chlorid  solution,  is  necessary.  Twenty  cubic  centi- 
meters of  the  above  solution,  corresponding  to  0.3056  gram  of 
the  salt,  are  placed  in  a  flat  porcelain  dish  having  a  diameter  of 
about  10  centimeters  and,  after  the  addition  of  five  cubic  centi- 
meters of  the  platinic  chlorid  solution,  evaporated  on  the  water- 
bath  with  constant  stirring  until,  after  cooling,  the  sirupy  liquid 
passes  quickly  into  a  fine  crystalline  condition.  The  evapora- 
tion can  be  carried  on  to  dryness  without  risk  in  the  use  of  the 
concentrated  salts.  In  addition  to  the  potassium  chloroplatinate, 
the  principal  ingredient  is  the  corresponding  sodium  salt,  and  this 
is  more  easily  dissolved  by  alcohol  when  dry  than  when  water  is 
present.  The  residue  is  rubbed  into  a  fine  powder  with  a  glass 
rod,  mixed  with  20  cubic  centimeters  of  96  per  cent,  alcohol,  and 
brought  onto  a  filter  moistened  with  alcohol  and  dried  at  120°, 

*°  Analytical  Methods  for  the  Examination  of  Potash  Salts,    Published 
by  the  Kalisyndikat,  Leopoldshall-Stassfurt,  1906. 


556  AGRICULTURAL  ANALYSIS 

and  washed  with  strong  alcohol,  care  being  taken  that  the  liquid 
does  not  touch  the  edge  of  the  filter.  The  filtration  can  be  car- 
ried on  under  a  moderate  pressure.  The  complete  washing  of 
the  potassium  platinochlorid  can  be  easily  accomplished  upon  the 
filter.  By  the  use  of  hot  alcohol  the  process  may  be  greatly 
hastened.  The  filter  and  the  precipitate,  after  as  much  of  the 
alcohol  wash  has  been  removed  as  is  possible,  are  dried  at  120° 
to  130°  to  constant  weight  and  weighed  while  still  warm.  One 
milligram  of  the  potassium  platinochlorid  thus  obtained  corre- 
sponds to  a  tenth  per  cent,  of  potassium  chlorid. 

(2)  By  Perchloric  Acid. — 13.455  grams  of  the  well  ground 
sample  are  dissolved  in  water  and  made  up  to  500  cubic  centi- 
meters after  the  addition  of  from  three  to  four  cubic  centi- 
meters of  the  acid  solution  of  barium  chlorid,  containing  122 
grams  of  the  crystallized  salt  and  50  cubic  centimeters  of  strong 
hydrochloric  acid  in  one  liter.  Twenty  cubic  centimeters  of  the 
filtrate  (=0.5382  gram  of  the  sample)  are  placed  in  a  shallow 
glass  or  blue  enamelled  porcelain  basin  of  about  10  centimeters 
diameter.  One  and  a  half  times  the  quantity  of  perchloric  acid  of 
1.125  specific  gravity  necessary  to  decompose  all  the  salts  is 
added.  The  mass  is  then  evaporated  on  the  water-bath  until  the 
odor  of  hydrochloric  acid  disappears,  and  white  fumes  of  per- 
chloric acid  begin  to  come  off.  After  cooling,  the  residue  is 
washed  with  96  per  cent,  alcohol  to  which  0.2  per  cent,  of  per- 
chloric acid  has  been  added.  In  washing,  20  cubic  centimeters  of 
the  alcohol  are  first  added  to  the  basin  and  the  residue  is  thor- 
oughly rubbed  down  in  the  liquid,  which  is  then  decanted  through 
a  tared  filter.  The  washing  is  repeated,  several  times  by  decanta- 
tion  and  finally  on  the  filter.  The  final  washing  requires  pure  al- 
cohol (as  little  as  possible)  to  remove  free  perchloric  acid.  The 
filter  and  residue  are  dried  and  weighed  in  the  same  manner 
as  in  the  platinum  process. 

One  milligram  potassium  perchlorate  represents  o.i  per  cent, 
of  potassium  chlorid. 

Estimation  of  Sodium  Chlorid. — For  the  estimation  of  the  so- 
dium chlorid  which  may  present  in  the  potassium  chlorid,  12.5 
grams  of  the  latter  salt  are  dissolved  in  a  quarter  liter  flask  with 


METHOD  FOR   CONCENTRATED  POTASH   SALTS  557 

25  cubic  centimeters  of  boiling  water  after  the  addition  of  90 
milligrams  potassium  carbonate  for  the  purpose  of  converting 
the  magnesium  and  calcium  compounds  into  carbonates.  To 
the  hot  solution  absolute  alcohol  is  added,  the  flask  well  shaken 
and  filled  to  the  mark  and  again  shaken  for  one  minute.  After 
filtration  100  cubic  centimeters,  corresponding  to  five  grams  of 
the  salt,  are  evaporated  to  dryness  in  a  porcelain  or  platinum  dish 
after  the  addition  of  a  few  drops  of  concentrated  hydrochloric 
acid  in  order  to  convert  any  potassium  carbonate  which  may  be 
present  into  chlorid.  The  residue  is  gently  ignited  and  weighed. 
In  this  mixture  of  potassium  and  sodium  chlorids  the  potassium 
chlorid  may  be  estimated  in  the  usual  way  and  the  sodium  chlo- 
rid determined  by  difference,  or  the  respective  proportions  of  the 
two  bases  may  be  calculated  after  the  determination  of  the  total 
chlorin  by  precipitation  with  a  standard  solution  of  silver  nitrate. 

Estimation  of  Magnesium  Chlorid. — In  order  to  estimate  the 
amount  of  magnesium  chlorid  in  high-grade  muriate  of  potash, 
25  grams  of  the  latter  salt  are  dissolved  in  a  half  liter  flask  and 
treated  with  10  cubic  centimeters  of  a  twice  normal  solution  of 
potash-lye.  The  flask  is  filled  to  the  mark  with  water,  thoroughly 
shaken  and  its  contents  filtered.  Fifty  cubic  centimeters  of  the 
filtrate  are  titrated  with  one-tenth  normal  sulfuric  acid.  The 
calcium  compounds  which  remain  in  solution  do  not  influence 
the  result.  The  quantity  of  magnesium  chlorid  originally  pres- 
ent corresponds  to  the  number  of  cubic  centimeters  of  the  nor- 
mal potash-lye  which  has  disappeared  in  the  operation.  The 
reaction  which  takes  place  is  represented  by  the  following  equa- 
tion :  MgCl2+2KOH=MgO2H2+ 2KC1. 

Sulfuric  Acid  in  Muriate  of  Potash. — Fifty  grams  of  the  sam- 
ple are  dissolved  in  500  cubic  centimeters  of  water.  After  fil- 
tering, 200  cubic  centimeters,  equivalent  to  20  grams  of  the  sam- 
ple, are  acidified  with  one  cubic  centimeter  of  concentrated  hy- 
drochloric acid  and  precipitated  at  boiling  temperature  with 
barium  chlorid.  After  standing  from  15  to  18  hours  the  pre- 
cipitate is  separated  by  filtration  and  weighed  in  the  usual 
manner. 

Potassium  Sulfate. — The  quantity  of  potassium   sulfate  con- 


558  AGRICULTURAL,  ANALYSIS 

tained  in  the  high  grade  sulfates  of  commerce  is  determined  in 
the  following  manner :  In  a  half  liter  flask  are  placed  8.9275 
grams  of  the  finely  ground  sample  which  is  dissolved  in  about  350 
cubic  centimeters  of  boiling  water  after  the  addition  of  20  cubic 
centimeters  of  hydrochloric  acid.  The  sulfuric  acid  is  thrown 
out  by  the  addition,  drop  by  drop,  of  a  barium  chlorid  solution. 
the  contents  of  the  flask  being  kept  boiling  meanwhile  and  thor- 
oughly stirred.  The  barium  chlorid  solution  is  delivered  from  a 
burette  with  a  glass  stop-cock.  From  time  to  time  the  addition 
of  the  barium  chlorid  is  stopped  and  the  upper  part  of  the  liquid 
allowed  to  become  clear  by  the  subsidence  of  the  barium  sulfate. 
It  is  then  noticed  whether  or  not  an  additional  drop  of  the  barium 
chlorid  solution  produces  a  turbidity.  A  convenient  method  is 
to  drop  a  small  crystal  of  barium  chlorid  into  the  clear  super- 
natant liquid.  Any  excess  of  barium  chlorid  is  removed  by  the 
careful  attention  of  sulfuric  acid.  After  the  precipitation  is  com- 
plete and  the  contents  of  the  flask  are  cooled,  it  is  filled  up  to 
the  mark  with  water  and  its  contents  filtered.  Twenty  cubic 
centimeters  of  the  filtrate,  corresponding  to  0.3571  gram  of  the 
original  salt  are  precipitated  by  platinic  chlorid  in  the  usual  man- 
ner and  the  resulting  potassium  platinochlorid  collected  and 
weighed.  One  milligram  of  the  potassium  platinochlorid  thus  ob- 
tained corresponds  to  one-tenth  per  cent,  of  potassium  sulfate  in 
the  original  salt.  To  the  percentage  of  potassium  sulfate  thus 
found  three-tenths  per  cent,  are  to  be  added  for  a  correction  when 
high-grade  potassium  sulfate  is  examined.  If  the  sample  be  a 
high-grade  sulfate  of  potassium  and  magnesium  no  correction 
should  be  applied. 

Estimation  of  Potassium  Chlorid  and  Potassium  Sulfate  in  Cal- 
cined Manurial  Salts. — In  these  salts  15.281  grams  of  potassium 
chlorid  or  17.847  grams  of  potassium  sulfate  are  dissolved  in  a 
half  liter  flask  after  the  addition  of  10  cubic  centimeters  of  hy- 
drochloric acid.  The  flask  is  filled  to  the  mark  and  its  contents 
filtered  and  250  cubic  centimeters  placed  in  a  half  liter  flask  and 
treated  with  barium  chlorid  solution  as  indicated  above.  The 
rest  of  the  operation  is  exactly  as  has  been  described.  In  each 


PREPARATION    OF    SOLUTIONS  559 

case  one  milligram  of  the  potassium  platinochlorid  corresponds  to 
one-tenth  per  cent,  of  the  desired  salt. 

By  Perchloric  Acid. — Dissolve  15.7225  grams  of  the  sample 
in  100  cubic  centimeters  of  boiling  water,  containing  30  cubic 
centimeters  of  concentrated  hydrochloric  acid,  in  a  liter  flask. 
The  rest  of  the  process  is  identical  with  that  described  above  for 
muriate  of  potash,  with  the  exception  that  a  smaller  excess  of 
barium  chlorid  is  required  and  that  instead  of  20  cubic  centimeters 
of  filtrate,  40  cubic  centimeters  are  evaporated.  One  milligram 
of  potassium  perchlorate  equals  o.i  per  cent,  of  potassium  sulfate. 
The  addition  of  0.3  per  cent,  should  be  made  under  the  same  con- 
ditions as  are  specified  under  muriate  of  potash. 

Estimation  of  Magnesium  Sulfate  in  Kieserit. — Ten  grams 
of  the  finely  powdered  kieserit  are  boiled  for  one  hour  in  a  half 
liter  flask  two-thirds  full  of  water.  After  cooling,  from  50  to 
60  cubic  centimeters  of  double  normal  potash-lye  and  20  cubic 
centimeters  of  a  10  per  cent,  neutral  potassium  oxalate  solution 
are  added,  the  flask  filled  to  the  mark,  and  after  being  well 
shaken  and  standing  for  a  quarter  of  an  hour,  filtered.  The  re- 
action is  represented  by  the  formula  MgSO4-(-2KOH=MgO2H., 
-I-K2SO4.  Fifty  cubic  centimeters  of  the  filtrate  are  then  titrated 
with  one-tenth  normal  sulfuric  acid.  To  the  percentage  of  mag- 
nesium sulfate  found  by  this  process  two-tenths  per  cent,  are  to 
be  added  as  a  correction. 

472.  Preparation  of  Solutions. — i.  Preparation  of  the  Platinic 
Chlorid  Solution. — The  platinum  scrap  or  recovered  waste  is 
dissolved  in  a  porcelain  basin  on  the  water  bath.  Four 
times  its  weight  of  pure  concentrated  hydrochloric  acid 
is  added,  and  while  warm  nitric  acid  is  gradually  introduced. 
Use  one  part  of  nitric  to  four  parts  of  hydrochloric  acid.  When 
the  platinum  has  been  dissolved,  the  solution  is  concentrated  by 
evaporation  until  a  drop  taken  upon  a  glass  stirring  rod  quickly 
deposits  crystals.  On  cooling  the  mass  assumes  a  crystalline  con- 
dition ;  it  is  then  taken  up  with  water  and  filtered.  The  solution  of 
platinic  chlorid  is  now  diluted  so  that  10  cubic  centimeters  contain 
one  gram  of  metallic  platinum.  Special  care  is  necessary  that  the 
solution  does  not  contain  platinous  chlorid  or  nitrous  compounds. 


560  AGRICULTURAL  ANALYSIS 

The  first  may  be  changed  into  platinic  chlorid  by  fuming  hydro- 
chloric acid  and  a  little  nitric  acid.  The  nitrous  compounds  may 
be  removed  by  the  alternate  addition  of  hydrochloric  acid  and 
water  during  evaporation.  It  has  further  to  be  noted,  that  by 
making  use  of  platinum  scrap  from  the  laboratory,  iridium  com- 
pounds may  be  present.  These  may  be  removed  by  precipitation 
with  ammonium  chlorid  and  subsequent  reduction. 

The  purity  of  the  platinic  chlorid  may  be  best  proved  by  con- 
ducting an  analysis  of  potassium  chlorid  formed  from  pure  mate- 
rials of  known  composition. 

2.  Perchloric  Acid. — An  acid  of  1.125  specific  gravity  should 
be  used  and  preparations  of  this  strength  are  now  offered  to  the 
trade. 

3.  The  Barium  Chlorid  Solution. — One  hundred  and  twenty- 
two  grams  of  the  crystallized  salt  with  50  cubic  centimeters  of 
concentrated  hydrochloric  acid  are  dissolved  in  water,  and  made 
up  to  one  liter. 

4.  The  Calcium  Saccharate  Solution. — Four  hundred  and  fifty 
grams  of  quicklime  and  450  grams  of  sugar  are  dissolved  in 
seven   liters  of  water.     After  shaking  thoroughly   for  half  an 
hour  the  resulting  precipitate  is  left  over  from  two  to  three  weeks. 
The  solution  is  then  filtered  and  a  further  450  gram  of  sugar 
is  added.     The  solution  should  preferably  be  stored  and  drawn 
off  in  a  closed  bottle  with  a  burette  attachment. 

5.  Alcohol. — For  washing  the  potassium  chloroplatinate  pre- 
cipitates, alcohol  of  at  least  96  per  cent,  purity  should  be  employed. 

6.  Filters. — The  most  serviceable  filter  for  the  platinic  chlorid 
estimation  of  potash  is  the  Swedish  filter,  Murktell  I  F.     Many 
otherwise  excellent  filter  papers  show  a  gain  in  weight  after  treat- 
ing with  96  per  cent,  alcohol  and  drying  at  120°.     This  may 
amount  to  several  milligrams  for  a  nine  centimeter  filter.     On 
this  account  it  is  advisable  in  taring  a  filter  to  omit  moistening  it 
with  alcohol  before  placing  in  the  drying  oven. 

473.  Lunge's  Modification  of  Technical  Methods. — The  tech- 
nical methods  for  the  determination  of  potash  in  the  Stass- 
furt  salts,  which  have  just  been  described,  are  of  great  interest 
to  agricultural  chemists  in  all  parts  of  the  world  since,  practical- 


LUNGE'S  MODIFICATION  OF  TECHNICAL  METHODS  561 

ly  all  the  potash  used  for  fertilizing  purposes  comes  from  this 
region.  The  methods  which  are  in  vogue  for  the  valuation 
of  the  product  are  both  of  a  scientific  and  commercial  importance. 
Lunge  has  tabulated  these  methods  in  convenient  form  for  refer- 
ence.41 The  methods  as  described  by  Lunge  are  very  nearly  the 
same  as  those  just  given,  but  are  modified  in  some  particulars. 

In  the  investigation  of  crude  salt  it  is  to  be  recommended  that  as 
large  a  sample  as  possible  be  used  in  order  to  eliminate  any  error 
which  might  arise  from  the  unequal  distribution  of  impurities  in 
the  crude  product.  The  estimation  of  potash  is  conducted  uni- 
formly by  the  platinum  method.  The  description  for  the  method 
of  complete  analysis  of  raw  salts  is  not  suitable  for  this  manual 
but  belongs  rather  in  the  domain  of  mineral  analyses.  It  is 
however,  sometimes,  of  interest  to  the  agricultural  analyst  to 
determine  the  quantity  of  chlorin  and  sulfuric  acid  in  the  raw 
salt  by  reason  of  the  injurious  effects  which  these  bodies  some- 
times produce. 

The  methods  for  the  complete  analysis  of  these  salts  are  given 
by  Lunge  in  the  article  referred  to  above.  The  method  for  the 
analysis  of  crude  salts  for  potash  alone  is  as  follows:  In  the 
case^  of  carnallit  and  bergkieserit  30.56  grams  of  the  salt  and  for 
kainit,  sylvinit  and  hartsalz  35.71  grams  are  boiled  in  a  500 
cubic  centimeter  flask  with  about  300  cubic  centimeters  of  water 
and  the  addition  of  15  cubic  centimeters  of  concentrated  hydro- 
chloric acid.  After  cooling,  the  flask  is  filled  to  the  mark.  The 
sulfuric  acid  in  50  cubic  centimeters  of  the  solution  or  of  the 
filtrate  is  precipitated  in  a  200  cubic  centimeter  flask  with  barium 
chlorid  and  after  cooling,  the  flask  is  filled  to  the  mark  and  20 
cubic  centimeters  of  the  filtrate  are  treated  with  a  sufficient 
quantity  of  the  platinum  chlorid  solution  in  a  flat  porcelain  dish 
of  about  10  cubic  centimeters  diameter  and,  with  frequent  shaking, 
the  mixture  is  evaporated  on  the  water  bath  until  the  residue 
is  of  a  sirupy  consistence  and  fumes  of  hydrochloric  acid  are  no 
longer  evolved.  On  cooling,  the  mass  solidifies  to  a  crystalline 
cake. 

The  formulation  of  large  crystals  of  sodium  platinochlorid  is 

41  Chemisch-technische  Untersuchungsmethoden,  5th  Edition,  1904,  1  : 
534- 


562  AGRICULTURAL   ANALYSIS 

to  be  as  carefully  avoided  as  possible  since  these  crystals  inter- 
fere with  the  subsequent  operation.  The  crystalline  residue  is 
rubbed  to  a  powder  with  a  broad  glass  rod  and  then  treated  with 
20  cubic  centimeters  of  alcohol  and  vigorously  stirred  and  rubbed 
and  the  solution  filtered  through  a  warm  filter  previously  dried 
to  a  constant  weight  at  from  120°  to  130°  and  moistened 
with  alcohol.  Care  is  to  be  taken  that  the  liquid  does  not  touch 
the  edge  of  the  filter.  This  operation  is  repeated  two  or  three 
times  upon  the  residue  remaining  in  the  dish  until  all  the  soluble 
platinum  double  salts  are  dissolved.  Favorable  results  will  be 
secured  the  sooner  if  at  the  time  of  the  second  treatment  with 
arcohol  the  dish  is  heated  until  the  alcohol  is  almost  boiling.  A 
less  content  of  platinum  chlorid  is  not  secured  in  this  way  because 
by  means  of  the  first  decantation  by  far  the  greater  part  of  those 
bodies  are  removed  which  are  apt  to  reduce  a  solution  of  potas- 
sium chlorid  in  alcohol.  The  well-washed  precipitate  is  collected 
upon  the  filter  and,  after  as  complete  as  possible  a  removal  of 
the  alcohol  by  suction  and  by  pressing  between  filter  paper,  dried 
at  120°  to  130°,  to  constant  weight.  Usually  20  minutes  are  suf- 
ficient for  that  purpose  and  the  mass  is  weighed  while  still  warm. 
Before  drying,  the  filter  is  carefully  folded  so  as  to  avoid  any 
loss  of  material  in  weighing.  Each  milligram  of  potassium  cor- 
responds to  one-tenth  per  cent,  of  potassium  chlorid  or  potassium 
sulfate. 

474.  The  Barium  Oxalate  Method. — The  principle  of  this  pro- 
cess, worked  out  by  Schweitzer  and  Lungwitz42  is  based  on  the 
fact  that  in  an  ammoniacal  solution,  by  means  of  barium  ox- 
alate,  all  the  alkaline  earths  can  be  precipitated  as  oxalates, 
and  sulfuric  acid  in  similar  circumstances  can  be  thrown  down 
as  a  barium  salt  and  the  iron  and  alumina  as  hydroxids.  The 
reagents  used  to  secure  this  precipitation  are  ammonia  and  barium 
oxalate. 

For  the  determination  of  potash  in  a  superphosphate  the  analyt- 
ical process  is  conducted  as  follows.     Ten  grams  of  the  super- 
phosphate are  mixed  with  half  a  liter  of  water  and   15  grams 
of  barium  oxalate  dissolved  in  hydrochloric  acid. 
41  Chemiker-Zeitung,  1894,  18  :  1320. 


METHOD  OF  DE  ROODE  FOR  KAINIT  563 

The  mixture  is  boiled  for  20  minutes  and  treated  with  some 
hydrogen  peroxid  to  oxidize  any  ferrous  iron  that  may  be  pre- 
sent. Afterwards  the  solution  is  made  alkaline  with  ammo- 
nia. After  cooling,  it  is  made  up  to  a  given  volume  (half  a  liter) 
and  filtered.  An  aliquot  part  of  the  filtrate  is  evaporated  to  dry- 
ness,  ignited,  extracted  with  hot  water,  and,  after  the  addition  of 
a  few  drops  of  hydrochloric  acid,  the  potassium  is  precipitated 
with  platinic  chlorid,  and  collected  and  weighed  in  the  usual 
manner:  Or  the  ignited  residue  may  be  dissolved  directly  in 
dilute  hydrochloric  acid  and  the  rest  of  the  process  carried  out 
as  indicated. 

In  kainit  the  process  is  conducted  as  follows :  Ten  grams  of 
the  powdered  sample  are  treated  with  a  hydrochloric  acid  solu- 
tion of  the  barium  oxalate  containing  10  grams  of  the  salt. 
The  rest  of  the  operation  is  conducted  as  described  above.  In 
the  use  of  this  method  it  is  important  that  always  enough  of  the 
barium  oxalate  solution  be  employed  to  fully  saturate  all  the 
sulfuric  acid  which  may  be  present. 

475.  Method  of  de  Roode  for  Kainit. — All  the  potash  contained 
in  kainit,  according  to  de  Roode,  passes  readily  into  aqueous 
solution.43  On  evaporating  this  aqueous  solution  to  a  pasty 
condition  with  enough  platinic  chlorid  to  unite  with  all  the  halo- 
gens present,  all  the  other  bodies  can  be  washed  out  of  the  potas- 
sium platinochlorid  by  ammonium  chlorid  solution  and  the  pure 
platinum  salt  thus  obtained,  which  is  washed  and  dried  in  the 
usual  way.  De  Roode  therefore,  asserts  that  it  is  quite  useless 
to  previously  precipitate  the  solution  of  kainit  with  barium  chlo- 
rid, ammonium  oxalate,  or  carbonate.  Before  the  addition  of  alco- 
hol to  the  residue  obtained,  by  evaporation  with  platinic  chlorid 
the  sodium  sulfate  present  renders  the  platinum  salt  sticky  and 
difficult  to  wash,  but  the  disturbing  sodium  compound  can  be 
readily  removed  by  washing  with  ammonium  chlorid  solution. 

The  method  of  direct  treatment  has  the  advantage  of  avoiding 
the  occlusion  of  potash  in  other  precipitates  and  the  danger  of 
loss  on  ignition.  The  method  as  used  by  de  Roode  gives  results 

43  Journal  of  the  American  Chemical  Society,  1895,  17  :  85. 


564  AGRICULTURAL  ANALYSIS 

about  one-tenth  per  cent,  higher  than  are  obtained  by  the  offi- 
cial processes. 

476.  The  Calcium  Chlorid  Method. — Huston  has  proposed  the 
addition  of  calcium  chlorid  to  the  solutoin  of  a  fertilizer  in  the 
determination  of  potash,  in  order  to  furnish  sufficient  calcium 
to  form  tricalcium  phosphate  with  all  the  phosphoric  acid  present, 
and  thereby  permit  the  use  of  platinum  dishes  in  the  lindo-glad- 
ding  method.44  In  testing  this  process  de  Roode  found  that  when 
sufficient  calcium  chlorid  was  added  to  combine  with  all  the  phos- 
phoric acid  present  and  then  ammonia  added  in  excess  and  a  por- 
tion of  the  solution  filtered,  no  test  for  phosphoric  acid  could  be 
obtained ;  but,  that  if  in  addition  to  the  calcium  chlorid  and  am- 
monia, some  ammonium  oxalate  or  carbonate  was  added,  a  fil- 
tered portion  of  the  solution  gave  a  test  for  phosphoric  acid.45 
This  is  accounted  for  by  the  fact  that  the  calcium  phosphate, 
which  is  precipitated  by  the  ammonia,  is  changed  by  the  ammo- 
nium oxalate  or  carbonate  into  calcium  oxalate  or  carbonate  and 
ammonium  phosphate,  so  that  the  very  object  for  which  the  cal- 
cium chlorid  was  added  is  defeated  by  the  addition  of  the  ammo- 
nium oxalate  or  carbonate.     In  order  to  make  the  use  of  calcium 
chlorid  effective  it  is  necessary  to  filter  the  liquid  from  the  precipi- 
tate formed  by  the  calcium  chlorid  and  ammonia  and  then  add 
the  ammonium  oxalate  or  carbonate  to  the  filtrate.     This  neces- 
sitates two  separate  filtrations  and  makes  the  proposed  method 
of  Huston  as  long  as  the  old  process. 

477.  Moore's   Potash   Method   for   Fertilizers   as   Modified   by 
Veitch. — In  reviewing  the  methods  used  and  proposed  for  estimat- 
ing potash  in  fertilizers  Veitch  has  suggested  that  the  losses  now 
occurring  may  be  partly  or  entirely  overcome  by  using  the  method 
of  Moore,  provided,  of  course,  any  potash  is  occluded  in  the 
ammonia  and  ammonium  oxalate  precipitate  in  the  lindo-glad- 
ding  method.46  The  addition  of  other  bases,  as  proposed  by  Hare 

14  Division  of  Chemistry,  Bulletin  43,  1894  :  26. 

*&  Journal  of  the  American  Chemical  Society,  1895,  17  :  46. 

**  Journal  of  the  American  Chemical  Society,  1905,  27  :  56. 

Fiinfter  internationaler  Kongress  fiir  angewandte  Chemie  ;  Bericht, 
1904,  1  :  486. 

Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  and  Edition, 
1906,  1  :  429. 


MOORE'S  POTASH  METHOD  FOR  FERTILIZERS  565 

in  the  lime-water  method,  appears  to  be  unnecessary  except  for 
the  purpose  of  saving  the  platinum  dishes  from  the  effects  of 
igniting  phosphates  in  the  presence  of  organic  matter. 

In  order  to  determine  the  applicability  of  the  method  to  this 
class  of  materials  several  modifications  were  tried,  the  purpose  of 
which  was  to  destroy  organic  matter  and  ammonium  salts  in 
the  most  expeditious  manner.  These  were  destroyed  both  by 
aqua  regia  and  by  igniting  in  porcelain  dishes,  the  potash  being 
taken  up  afterward  in  distilled  water  and  also  in  water  acidified 
with  hydrochloric  acid.  In  all  cases  the  results  have  been  given 
corrected  and  uncorrected  for  the  undissolved  foreign  salts.  In 
cases  where  the  ignited  residue  was  taken  up  only  in  distilled 
water  the  impurities  in  the  precipitate  were  sometimes  consider- 
able. Comparisons  were  also  made  of  washing  with  plain  alco- 
hol and  with  acidified  alcohol.  The  results  are  given  in  the  follow- 
ing table. 

The  samples  represented  mixtures  of  the  commoner  raw  ma- 
terials. 

No. 

1759  Acid  phosphate. 

1761  Acid  phosphate  and  cottonseed  meal. 

1762  Acid  phosphate  and  muriate  of  potash. 

1763  Acid  phosphate  and  muriate  of  potash,  cottonseed  meal  and 

nitrate  of  soda. 

2119  Peruvian  guano. 

2120  Mixed  fertilizer. 

291  r         Acid  phosphate  and  potash  salts. 

2912         Dissolved  animal  bone  and  potash  salts. 

TABLE  SHOWING  PERCENTAGE  OF  POTASH  IN  FERTILIZERS. 

Moore's  Method 


Official 

No.  method. 

1759  4.98 

1761  0.92 

1 762  o.  70 

1763  5.70 
2119  3.88 

2120  3.60 

2911  3.96 

2912  4.08 


Organic  matter  and  NH3  salts  destroyed  with  HNOS  +  HC1 

-*. 

Acid  alcohol 

Plain  alcohol 

KjO  +  undis. 

Corrected 

K2O  4-  undis. 

Corrected 

Fill,  on  paper 

salts 

tfso. 

salts. 

K2O 

corrected. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

5.10 

5-01 

5-25 

5-17 

5-31 

1.02 

0.87 

1-37 

0.85 

0.97 

0.68 

0.62 

0.99 

0.67 

0.87 

6.17 

6.13 

6.58 

6.19 

5.85 

4.00 

3-96 

3-74 

3-71 

3-92 

3-72 

3.69 

3-82 

3.78 

3-67 

4.04 

3-99 





4-14 

4.13 







Ignited  in  porcelain 

Dissolved 

K2O  +  undis. 
salts. 
Per  cent. 

in  HC1 

Dissolved  in  H2O 

Corrected 
K20. 
Per  cent. 

K2O  +  undis.          Corrected 
salts.                       K2O. 
Per  cent.               Per  cent. 

.... 

4.96 
1-05 

4.92 
0.8l 

4.84 
0.79 

6.21 

0.92 
6.16 

1.43 
6.13 

0.79 

5-97 

3-47 
3.83 
4.01 
4.08 

3-44 
3-75 
3.83 
3-93 

3-50 
3-70 
2.09 
2.25 

3-49 
3-68 
2.08 
2.24 

AGRICULTURAL  ANALYSIS 
TABLE  SHOWING  PERCENTAGE  OF  POTASH  IN  FERTILIZERS. — Cont. 

Moore's  Method 


Official 
No.  method. 

1759  4.98 

1761  0.92 

1762  0.70 

1763  5-70 

2119  3.88 

2120  3.60 

2911  3.96 

2912  4.08 

As  a  rule,  the  results  are  slightly  higher  by  the  moore  method 
than  by  the  official  method;  this  is  only  noticeably  so  in  case  of 
sample  1/63.  From  this  it  would  appear  that  the  flocculent  pre- 
cipitate of  iron  and  lime  phosphate  has  but  little  to  do  with  the 
low  results  usually  obtained.  It  is  to  be  noticed  that  only  when 
the  acid  alcohol  is  used  may  the  impurities  contained  in  the  plati- 
num precipitate  be  neglected.  Where  plain  alcohol  is  used  it  is 
usually  necessary  to  dissolve  the  potassium  chlorplatinate,  wash, 
and  re-weigh  the  crucible  to  obtain  the  true  weight  of  the  potash. 

It  is  obvious  that  after  igniting  the  material  it  is  not  suffi- 
cient to  treat  it  with  water  alone  in  order  to  dissolve  the  potash ; 
such  procedure  does  not  always  secure  all  the  potash,  some  of  it 
remaining  undissolved,  possibly  in  complex  silicates  or  phospho- 
silicates,  adhering  to  the  dish.  It  was  found  that  the  potash  so 
held  could  usually  be  readily  recovered  by  dissolving  the  ignited 
material  in  the  dish  in  dilute  hydrochloric  acid.  This  is  not 
always  true,  however,  the  potash  so  held  being  dissolved  but 
slowly  in  some  instances,  and  while  it  appears  that  all  potash  may 
be  recovered  by  prolonged  treatment,  the  process  is  not  con- 
sidered to  have  any  advantages  over  the  official  method. 

478.  Estimation  of  Potash  by  the  Platinum  Method  in  the 
Presence  of  Sulfates  of  the  Alkalies  and  Alkaline  Earths. — Regel 


ESTIMATION  OF  POTASH   BY   PLATINUM    METHOD  567 

calls  attention  to  the  difficulties  attending  the  ordinary  method  of 
determining  potash  in  the  presence  of  the  sulfates  of  the  alkalies 
and  alkaline  earths.47  He  modifies  the  method  by  precipitating 
the  potash  directly  without  previous  precipitation  with  barium 
chlorid.  This,  however,  is  not  a  new  variation,  as  Regel  sup- 
poses, since  it  is  the  basis  of  the  one  proposed  by  Moore  and 
practiced  with  such  success  in  this  country  for  many  years.  The 
precipitate  of  the  platinum  potash  salt  is  washed  in  the  usual  man- 
ner. If  sodium  sulfate  is  present  some  of  this  is  contained  in  the 
precipitate.  In  this  case  the  precipitate  is  washed  into  a  small 
beaker,  the  parts  remaining  on  the  filter  being  dissolved  in  hot 
water  and  powdered  magnesium  is  added  in  excess.  It  is  to  be 
noticed  that  the  magnesium,  even  in  almost  completely  neutral 
solutions,  reduces  the  double  salt.  Upon  its  introduction  there 
is  a  notable  evolution  of  heat  and  a  decomposition  of  the  neutral 
salt  with  a  separation  of  black,  finely  divided  metallic  platinum 
The  precipitate  of  platinum  is  separated  by  filtration  and  any  ex- 
cess of  magnesium  removed  by  washing  with  dilute  hydrochloric 
acid.  The  separated  platinum  is  dried,  ignited,  and  weighed. 
If  magnesium  sulfate  or  calcium  sulfate  is  present  in  the  original 
platinum  precipitate,  the  method  of  separation  is  exactly  the  same 
as  that  just  described  except  that  five  per  cent,  nitric  acid  is 
used  instead  of  hydrochloric  acid  for  the  solution  of  any  excess 
of  sulfates.  In  this  way  calcium  sulfate  in  the  quantities  in  which 
it  is  present  in  potash  salts  is  completely  removed. 

The  reasons  for  using  nitric  acid  are  the  following: 

If  the  mixture  of  metallic  platinum  and  the  residual  salts  is 
treated  with  hydrochloric  acid,  the  filtrate  is  clear.  If,  however, 
an  attempt  be  made  to  wash  out  the  hydrochloric  acid  with  water 
there  is  obtained  a  deep  black  tinted  filtrate  containing  dissolved 
platinum  from  which  metallic  platinum  separates  slowly.  This 
phenomenon  only  occurs  if  the  platinum  salts  are  mixed  with  con- 
siderable quantities  of  potassium  chlorid  or  calcium  sulfate,  a 
fact  for  which  up  to  the  present  time  no  satisfactory  explanation 
has  been  made.  Since  the  separation  of  the  platinum  from  the 

47  Chemiker-Zeitung,  1906,  30  :  684. 


568  AGRICULTURAL   ANALYSIS 

blackened  filtrate  doubtless  occurs  through  the  action  of  the 
•oxygen  of  the  air,  it  was  sought  to  prevent  the  solution  of  the 
platinum  beforehand  by  the  use  of  a  substance  like  nitric  acid 
easily  giving  off  oxygen. 

479.  Rapid  Control  Method  for  Potash  Salts. — For  rapid  con- 
trol work  where  great  accuracy  is  not  required,  Albert  recom- 
mends that  the  finely  ground  substance  be  placed  in  a  liter  flask 
and  about  400  cubic  centimeters  of  water  added  and  three  cubic 
centimeters  of  hydrochloric  acid.48  After  boiling,  barium  chlorid 
is  added,  drop  by  drop,   as  long  as   a  precipitate  is  produced. 
After  cooling,  the  flask  is  filled  to  the  mark  and  shaken  and  its 
•contents   filtered   through  a   dry   filter.     An   aliquot   portion   of 
the  filtrate  is   evaporated   with   platinum   chlorid   solution   in  a 
smooth  porcelain  dish  almost  to  dryness  and  the  mass  treated 
with  alcohol,  filtered  through  a  weighed  filter,  and  well  washed 
with  alcohol.     The  filter  is  then  dried  in  an  air-bath  to  a  con- 
stant .weight.     For  the  different  kinds  of  potash  materials  on  the 
market  the  following  proportions  are  recommended : 

Kainit  or  Carnallit. — Twenty  grams  in  one  liter:  Fifty  cubic 
centimeters  of  the  filtrate  are  evaporated  with  40  cubic  centime- 
ters of  platinic  chlorid  solution.  The  weight  of  potassium  platino- 
chlorid  obtainedXi9-3  gives  the  per  cent,  of  K2O. 

Sulfate  of  Potash. — Fifteen  grams  in  one  liter :  Twenty  cubic 
centimeters  of  the  solution  are  evaporated  with  15  cubic  centi- 
meters of  platinic  chlorid.  The  weight  of  potassium  platinochlo- 
rid  obtained X 64.33  gives  the  per  cent,  of  K2O. 

Potassium  Chlorid. — Ten  grams  in  one  liter.  Twenty-five  cub- 
ic centimeters  are  evaporated  with  15  cubic  centimeters  of  platinic 
chlorid  solution.  The  weight  of  the  precipitate  obtained  X  77-2 
gives  the  per  cent,  of  K2O. 

480.  Weighing  the  Precipitate  as  Metallic  Platinum. — Hilgard 
calls   attention  to   the   difficulty   of   weighing   the   double   chlo- 

48  Zeitschrift  fur  angewandte  Chetnie,  iSgr,  4  :  281. 


WEIGHING  THE   PRECIPITATE  569- 

rid  of  platinum  and  potash  as  such,  although  he  acknowledges 
that  in  the  gooch  this  weighing  can  be  made  with  great  accu- 
racy.49 He  prefers  to  estimate  the  platinum  in  the  metallic 
state  and  uses  for  this  purpose  a  platinum  crucible  the  inside  of 
which,  half  way  up  from  the  bottom,  is  coated  with  a  layer  of 
platinum  sponge,  which  is  conveniently  prepared  by  the  decom- 
position of  a  few  decigrams  of  the  platinum  double  salt  by  in- 
clining the  crucible  and  rotating  it  during  the  progress  of  the 
reduction,  which  should  require  about  a  quarter  of  an  hour.  The 
platinum  sponge  produced  in  this  way  greatly  favors  the  decompo- 
sition of  the  double  salt  for  analytical  purposes.  The  decompo- 
sition of  the  salt  takes  place  quickly  and  quietly  and  at  conven- 
iently low  temperatures. 

When  the  decomposition  is  ended  the  crucible  is  strongly 
heated  so  as  to  hold  the  platinum  sponge  together  sufficiently  to 
prevent  its  being  removed  in  the  subsequent  washing  of  the  cru- 
cible by  decantation.  By  the  ignition  at  a  high  temperature 
necessary  to  secure  this,  the  greater  part  of  the  potassium  chlorid 
is  volatilized.  After  cooling,  a  few  drops  of  concentrated  hydro- 
chloric acid  are  placed  in  the  crucible  and  if  the  slightest  yellow 
color  be  shown  the  acid  is  evaporated  and  the  ignition  repeated, 
with  the  addition  of  a  little  oxalic  acid.  In  most  cases  the  slight 
yellow  color  produced  comes  from  a  trace  of  iron  and  will,  there- 
fore, appear  again  after  the  second  ignition.  The  crucible  is  sub- 
sequently washed  by  repeated  decantations,  finally  with  boiling 
water,  and  after  drying  is  ignited  and  weighed. 

The  advantage  of  this  process  is  that  without  further  trouble 
the  reduced  metal  is  completely  freed  of  any  salts  of  the  alkaline 
earths,  etc.,  which  have  been  carried  down  with  it  and  also  from 
any  of  the  uncombined  sodium  chlorid  which  may  not  have 
been  washed  out  by  the  alcohol.  In  fact,  the  results  obtained 
in  this  way  are  nearly  always  lower  than  those  obtained  through 
the  direct  weighing  of  the  double  salt,  and  the  wash  water  which 
is  first  poured  off  contains,  as  a  rule,  traces  of  the  alkaline  earths 
and  almost  without  exception  some  sodium  chlorid.  Correction 
49  Zeitschrift  fur  analytische  Chemie,  1893,  32  :  184. 


57O  AGRICULTURAL  ANALYSIS 

for  the  filter  ash  is  unnecessary  because  the  ash  is  completely 
dissolved  by  the  treatment  received.  The  platinum  sponge 
which  is  collected  in  the  crucible  in  this  way  is  removed  in  case 
it  does  not  adhere  to  the  sides  and  the  crucible  is  then  ready  for 
the  next  operation. 

481.  Sources  of  Error  in  the  Platinum  Method. — In  the  com- 
parative work  done  in  the  determination  of  potash  by  the  mem- 
bers of  the  Association  of  Official  Agricultural  Chemists  there 
has  been  noted,  from  year  to  year,  marked  differences  in  the  data 
obtained  by  different  analysts.  Such  differences  often  are  due 
•to  personal  errors,  or  a  failure  to  accurately  follow  the  directions 
for  manipulation.  Sometimes,  however,  they  are  due  to  sources 
of  error  in  the  processes  employed.  In  the  platinum  method  these 
sources  of  error  have  been  long  known  to  exist.  Chief  among 
these  is  the  remarkable  facility  with  which  potash  becomes  in- 
corporated with  the  precipitates  of  other  bodies.  The  character 
and  magnitude  of  some  of  these  errors  have  been  studied  by 
Robinson.50  • 

Many  precipitates  occlude  potash  and  hold  it  so  firmly  that 
it  cannot  be  washed  out  with  hot  water  although  the  potash 
compounds  present  in  the  precipitate  are  perfectly  soluble.  It 
appears  to  be  a  kind  of  molecular  adhesion.  Barium  sulfate 
has  this  property  of  attaching  potash  molecules  in  a  high  degree, 
and  ferric  and  aluminic  compounds  only  to  a  slightly  less  extent. 
To  reduce  the  losses,  consequent  on  the  conditions  just  men- 
tioned, to  a  minimum,  the  sulfuric  acid  and  earthy  bases  should 
be  very  slowly  precipitated,  with  violent  agitation,  at  a  boiling 
temperature. 

Another  source  of  loss  in  the  platinum  method  arises  from  the 
use  of  a  solution  of  ammonium  chlorid  for  washing  the  potassium 
platinochlorid  precipitate.  There  is  danger  here,  not  only  of 
the  solution  of  the  impurities  present  in  the  precipitate,  but  also 
of  a  double  decomposition  by  means  of  which  some  ammonium 
40  Journal  of  the  American  Chemical  Society,  1894,  16  :  364. 


EFFECT  OF  CONCENTRATION  571 

may  be  substituted  for  the  potassium  in  the  washed  product. 
In  the  official  method,  moreover,  there  is  danger  of  securing  a 
final  precipitate  which  may  contain  traces  of  calcium  and  mag- 
nesium sulfates  when  these  bodies  are  abundantly  present  in  the 
sample  used  for  analysis.  The  careful  analyst  must  guard 
against  these  sources  of  error,  but  it  is  probably  true  that  he 
will  never  secure  a  practically  chemically  pure  precipitate  of 
potassium  platinochlorid  when  working  on  the  mixed  fertilizers 
found  in  commerce. 

482.  Effect  of  Concentration  on  the  Accuracy  of  Potash  Analy- 
sis.— Winton  has  also  studied  the  sources  of  error  in  the  deter- 
mination of  potash  as  platinochlorid,  especially  with  reference 
to  the  effect  of  the  concentration  of  the  solution  at  the  time  of 
precipitation.51 

He  finds  that  the  method  of  precipitating  in  concentrated 
solutions  and  drying  the  potassium  platinochlorid  at  130°,  depends 
for  its  accuracy  upon  the  mutual  compensation  of  three  errors; 
viz.,  ( i )  due  to  the  solubility  of  the  potassium  salt  in  80  per  cent, 
alcohol,  (2)  due  to  the  presence  of  water  in  the  crystals  which  is 
not  driven  off  at  130°,  and  (3)  due  to  the  use  of  a  factor  based 
on  the  wrong  atomic  weight  of  platinum. 

He  finds,  further,  that  the  error  due  to  the  presence  of  water 
occluded  in  the  crystals  can  be  reduced  to  a  minimum,  and  the 
process  of  drying  greatly  simplified,  by  adding  the  solution  of 
platinum  chlorid  to  the  potash  solution  in  a  dilute  condition,  not 
exceeding  one  per  cent,  in  strength.  The  potassium  platinochlo- 
rid thus  produced  can  be  very  effectively  dried  at  100°.  The 
error  due  to  the  solubility  of  the  salt  in  80  per  cent,  alcohol  can 
also  be  greatly  reduced  by  using  95  per  cent,  alcohol.  The  error 
due  to  the  wrong  factor;  viz.,  0.3056  based  on  the  old  atomic 
weight  of  platinum,  can  be  corrected  by  using  the  factor  based 
on  the  recently  determined  atomic  weight  of  platinum;  viz.,  195, 
which  is  0.30688. 

Since  Winton's  paper  was  published  the  atomic  weight  of  plati- 
51  Journal  of  the  American  Chemical  Society,  1895,  17  :  453. 


572  AGRICULTURAL  ANALYSIS 

num  has  been  reduced  to  194.8,  so  that  the  factor  on  this  basis 
is  0.3071. 

483.  Differences  in   Crystalline  Form. — Winton   has   also  ob- 
served a  distinct  difference  in  the  crystals  of  potassium  platino- 
chlorid  when  obtained  from  concentrated  and  dilute  solutions.52 
When  platinic  chlorid   is  added  to   a  concentrated  solution  of 
potassium  chlorid,  a  large  part  of  the  salt  which  is  formed  is 
precipitated  in  a  pulverulent  state,  the  remainder  being  depos- 
ited on  evaporation.     After  treating  with  alcohol,  filtering,  and 
drying,  the  double  salt  is  found  in  the  state  of  a  fine  powder 
which,  when  examined  under  the  microscope,  is  found  to  consist 
largely  of   radiating  crystals.     The   characteristic   form   is  one 
having  six  arms  formed  by  the  intersection,  at  right  angles,  of 
three  bars.     Numerous  globular  cavities  in  the  crystals  are  ob- 
served in  which  mother  liquid  is  enclosed.     For  this  reason  the 
salt  is  not  easily  dried  at  100°,  but  when  so  dried  loses  additional 
moisture  at  130°,  and  still  more  at  160°.     The  total  additional 
loss,  after  drying  at  100°,  from  this  cause  may  amount  to  as 
much  as  six-tenths  per  cent,  of  potassium  chlorid. 

When,  however,  the  solution  of  the  potassium  salt  is  so  dilute 
that  no  precipitate  at  all  is  formed  on  the  addition  of  platinic 
chlorid,  the  double  salt  is  all  deposited,  as  well  as  formed  slowly, 
during  the  evaporation  and  occurs  exclusively  as  octahedra.  These 
octahedra  are  comparatively  free  of  cavities,  and  give  up  practical- 
ly all  their  moisture  when  dried  at  100°.  A  method  of  proced- 
ure, therefore,  for  potash  determination,  based  on  the  above  prin- 
ciple of  the  addition  of  the  reagent  to  dilute  solutions,  and  dry- 
ing the  double  salt  produced  upon  evaporation,  after  washing 
with  95  per  cent,  alcohol  at  100°,  and  using  the  factor  0.3071 
for  potassium  chlorid  and  0.1941  for  potassium  oxid,  gives  good 
results  and  is  regarded  as  better  than  any  of  the  methods  which 
prescribe  the  addition  of  platinic  chlorid  to  highly  concentrated 
potash  solutions. 

484.  Factors  for  Potash  Estimation. — The  factor  now  in  use 
by  the  official  chemists  to  convert  potassium  platinochlorid  into 
potash   (K2O)   is  0.1941,  and  for  potassium  chlorid  0.3071. 

M  Journal  of  the  American  Chemical  Society,  1895,  17  :  453- 


RECOVERY   OE    THE    PLATINUM    WASTE  573 

Wolfbauer  gives  the  differences  which  may  arise  by  computing 
the  potash  from  its  double  platino  chlorid  by  the  different  values 
-assigned  to  the  atomic  weight  of  platinum.03 

The  common  factor  used  at  that  time  to  obtain  potassium  chlo- 
rid from  potassium  platinochlorid  was  based  on  the  atomic 
weight  197.18  and  is  derived  from  the  formula: 

2(39-13  +  35.46)  =  149-18  = 

2  X  39-13  +  I97.I8  +  6  X  35-46       488.20 
The  variations  arising  from  taking  other  assigned  values  for 
the  atomic  weight  of  platinum  are  shown  in  the  following  table : 


Factor  for  potassium 

Relation  to  factor  0.30557 

chloric 

1  from 

in  per 

cent. 

Atomic 

Determined  by 

Potassium 

Potassium 

weight  of 

or  calculated 

platino- 

platino- 

platinum 

by 

chlorid 

Platinum 

chlorid 

Platinum 

197.18 

Berzelius 

0.30557 

0.75658 

IOO.OO 

100.00 

197.88 

Andrews 

0.30517 

0-7539° 

99.86 

99-65 

I95-06 

Haberstadt 

0.30690 

0.76468 

100.44 

101.07 

194.87 

Seubert  and  Clarke 

0.30702 

0.76555 

100.47 

IOI.2O 

The  factor  0.3056  was  regarded  as  the  best  for  the  computation 
from  potassium  platinochlorid  and  0.7566  from  platinum.  It  was 
also  suggested  that  it  is  better  to  make  the  computation  from  the 
reduced  platinum  than  from  the  double  salt.  Accepting  the  atom- 
ic weight  of  platinum  as  194.8,  the  factor  last  given  in  the  above 
table  is  almost  correct. 

485.  Recovery  of  the  Platinum  Waste  and  Preparation  of  the 
Platinic  Chlorid  Solution. — (i)  By  reduction  in  Alkaline  Alco- 
hol.— All  nitrates  containing  platinic  chlorid,  all  precipitates  of 
potassium  platinochlorid  and  all  residues  of  metallic  platinum 
should  be  carefully  preserved  and  the  platinum  recovered  there- 
from by  the  following  process:  The 'platinum  residues  are  placed 
in  a  large  porcelain  dish.  Since  these  residues  contain  a  large 
amount  of  alcohol,  they  should  be  diluted  with  about  one-third 
their  volume  of  water,  and  when  boiling  treated  with  some  sodium 
carbonate.  The  solid  potassium  platinochlorids  should  not  be  ad- 
-ded  until  the  liquid  is  boiling,  and  then  only  little  by  little.  The 
heating  on  the  water  bath  is  continued  until  the  liquid  floating 
-over  the  platinum  sponge  is  quite  clear  and  only  slightly  yellow. 
58  Chemiker-Zeitung,  1890,  4  :  1246. 


574  AGRICULTURAL  ANALYSIS 

The  liquid  is  then  poured  off  and  the  reduced  platinum  purified  by 
boiling  with  hydrochloric  acid  and  water.  It  is  then  dried  and 
ignited  to  destroy  any  organic  matter  which  may  be  present.  It  is 
advisable  to  boil  the  finely  divided  platinum  once  with  strong  nitric 
acid,  and  after  this  is  poured  off  the  solution  of  the  platinum  is 
effected  in  a  large  porcelain  dish  over  a  water  bath  by  adding 
about  four  times  its  weight  of  hydrochloric  acid,  warming,  and 
adding  nitric  acid,  little  by  little.  After  the  platinum  is  in  solu- 
tion the  evaporation  is  continued  until  a  drop  of  the  liquid,  re- 
moved by  a  glass  rod,  quickly  solidifies.  The  crystalline  mass 
which  is  formed  on  cooling  is  taken  up  with  water  and  filtered, 
and  then  a  sufficient  amount  of  water  added  so  that  each  10  cubic 
centimeters  will  contain  one  gram  of  platinum.  The  specific 
gravity  of  this  solution  is  1.18  at  ordinary  temperatures.  Special 
care  must  be  taken  that  the  solution  contains  neither  platinous 
chlorid  nor  nitrogen  compounds.  If  the  first  named  compound 
be  present  it  should  be  converted  into  platinic  chlorid  by  treat- 
ment with  fuming  hydrochloric  acid  and  a  little  nitric  acid.  The 
last  mentioned  compound  may  be  removed  by  evaporating  suc- 
cessively with  hydrochloric  acid  and  water.  If  the  platinic  chlorid 
be  made  from  waste  platinum,  the  danger  of  contamination  with 
indium  must  be  considered.  In  such  a  case  the  platinum  should 
be  separated  as  ammonium  platinochlorid,  which  can  afterwards 
be  reduced  as  above  indicated.  A  convenient  test  of  the  purity 
of  platinic  chlorid  solution  is  accomplished  by  the  precipitation 
of  a  known  weight  of  chemically  pure  potassium  salt,  and  deter- 
mining the  quantity  of  platino-potassium  chlorid  produced. 

(2)  By  Reduction  in  Nascent  Hydrogen. — The  platinum  resi- 
dues, filtrates  containing  platinum,  etc.,  are  collected  in  a  large 
flask  and  evaporated  in  a  large  dish  on  a  water  bath,  and  re- 
duced by  means  of  zinc  and  hydrochloric  acid  to  metallic  plati- 
num, the  mass  being  warmed  until  all  the  zinc  has  been  dis- 
solved. The  supernatant  liquid  standing  over  the  spongy  plati- 
num is  decanted  and  the  spongy  mass  boiled  twice  with  distilled 
water.  The  spongy  platinum  is  then  brought  on  a  filter  and 
washed  till  the  filtrate  shows  no  acid  reaction.  The  filter  and' 
platinum  sponge  are  next  incinerated  in  a  platinum  dish  and  the 


CHLORPLATINIC    ACID    BY    ELECTROLYSIS  575 

residue  weighed.  The  weighed  mass  of  pure  platinum  is  dis- 
.solved  in  hydrochloric  acid,  with  the  addition  of  as  little  nitric 
acid  as  possible,  and,  after  cooling,  filtered.  The  filtrate  is  after- 
Awards  evaporated  in  a  porcelain  dish  on  a  water  bath  to  a  sirupy 
consistence,  taken  up  with  water  and  filtered.  To  this  filtrate 
enough  water  is  now  added  to  make  the  solution  correspond  to 
one  gram  of  metallic  platinum  in  10  cubic  centimeters. 

486.  Preparation  of  Chlorplatinic  Acid  by  Electrolysis. — It  has 
been  noticed  when  using  aqua  regia  to  dissolve  plati- 
num that  traces  of  nitric  acid  are  removed  with  great  difficulty, 
even  by  repeated  evaporation.  Weber  has  called  attention  to 
the  fact  that  when  working  with  as  much  as  100  grams  of  plati- 
num, repeated  evaporation  to  dryness  of  the  solution  is  tedious 
.and  yields  unsatisfactory  results.  If  hydrochloric  acid  be  used 
in  the  evaporation  large  quantities  of  material  are  necessary, 
while  with  water  there  is  danger  of  decomposition  of  the  chlor- 
platinic  acid  and  consequent  contamination  with  hydroxychlor- 
platinates.54  To  avoid  these  conditions  the  following  method 
-of  preparing  the  platinum  reagent  is  used. 

Platinum  scraps,  or  sponge,  are  dissolved  in  aqua  regia,  the 
•excess  of  acid  removed  either  by  neutralization  or  evaporation, 
and  the  platinum  solution  reduced  by  zinc  or  alkaline  formate, 
preferably  the  latter.  The  liquid  is  decanted  from  the  precipi- 
tated platinum  and  the  latter  is  warmed  with  a  little  dilute  hy- 
drochloric acid  to  remove  iron.  The  platinum  is  transferred  to 
the  electrolytic  apparatus,  which  is  constructed  as  follows: 

The  apparatus  (Fig.  47)  is  made  of  a  cylindrical  tube  four 
centimeters  in  diameter  and  35  centimeters  long,  ending  in  a 
narrow  glass  tube  of  about  four  millimeters  bore,  shaped  in  the 
form  of  a  siphon.  The  anode  consists  of  a  thin  disk  of  sheet 
platinum,  closely  fitting  into  the  tube,  and  perforated  with  small 
holes.  A  short  piece  of  platinum  wire  is  welded  to  the  disk  and 
carried  through  the  glass  tube,  as  shown  in  the  figure.  The 
-other  end  of  the  platinum  wire  ends  in  a  glass  tube  which  is 
carried  to  the  top  of  the  apparatus  and  filled  with  mercury.  The 
platinum  disk  is  about  30  centimeters  from  the  top  of  the  ap- 
paratus, and  is  placed  at  a  point  where  the  tube  begins  to  be- 
54  Journal  of  the  American  Chemical  Society,  1908,  80  :  29. 


576 


AGRICULTURAL   ANALYSIS 


come  narrow.  The  space  below  the  anode  is  filled  with  glass 
beads  to  support  the  platinum  disk.  About  five  centimeters- 
from  the  top  of  the  tube  three  shoulders  are  moulded  into  the 


Fig.  47.    Apparatus  for  Making  Pure  Chlorplatinic  Acid. 

tube  and  on  these  the  cathode  chamber  is  suspended,  as  shown  inr 
the  figure.  This  chamber  consists  of  a  porous  porcelain  filter 
about  1 8  centimeters  long  and  25  millimeters  in  diameter.  The 
cathode  consists  of  a  sheet  of  platinum  from  four  to  five  centi- 
meters long  and  from  two  to  three  centimeters  wide,  carrying 
a  platinum  wire  passing  through  a  glass  tube  as  shown.  This 
tube  is  suspended  from  a  perforated  watch  glass  which  serves 
also  as  a  cover  for  the  apparatus.  The  whole  apparatus  is  sus- 


CHLORPLATINIC  ACID  BY  ELECTROLYSIS  577 

pended  in  a  long  cylinder  when  necessary  so  that  it  may  be 
brought  to  any  desired  temperature  by  surrounding  it  with  wa- 
ter. This  outer  tube  is  not  shown  in  the  figure  and  may  be  dis- 
pensed with  when  low  currents  are  used.  When  the  current 
rises  to  10  amperes,  the  cooling  jacket  is  essential  to  prevent  the 
apparatus  from  becoming  hot. 

The  reduced  platinum  to  be  treated  is  placed  on  the  anode  plate, 
and  is  washed  with  dilute  hydrochloric  acid  until  clean.  The 
wash  waters  are  drawn  off  through  the  siphon  S.  After  wash- 
ing, the  platinum  is  covered  with  concentrated  hydrochloric 
acid,  in  quantity  sufficient  to  have  it  stand  in  the  tube  on  a  level 
with  the  end  of  S  when  the  porous  cylinder  is  inserted  which 
is  filled  to  the  top  with  hydrochloric  acid. 

The  current  for  electrolysis  may  be  taken  from  a  120  volt 
direct  current  by  inserting  a  number  of  incandescent  lamps  par- 
allel with  each  other  and  in  series  with  the  cell.  The  cell  may 
be  run  continuously  on  from  eight  to  10  amperes,  and  with  this 
strength  64  grams  of  platinum  may  be  dissolved  in  four  or  five 
hours.  The  theoretical  quantity  for  36  ampere  hours  is  65 
grams.  While  the  apparatus  is  in  operation  the  hydrochloric 
acid  travels  from  the  cathode  cell  to  the  anode  under  the  in- 
fluence both  of  gravity  and  electric  endosmosis.  By  adjust- 
ment of  the  hight  of  hydrochloric  acid  in  the  anode  cell  the 
heavy  layer  of  chlorplatinic  solution  as  it  is  formed  is  delivered 
at  the  tip  of  the  siphon  S  drop  by  drop,  or  the  flow  may  be 
started  by  gentle  suction  at  that  point.  The  acid  in  the  cathode 
chamber  is  replenished  from  time  to  time  as  it  becomes  neces- 
sary. Towards  the  end  of  the  operation,  when  the  amount  of 
platinum  remaining  on  the  perforated  disk  becomes  small,  bubbles 
of  chlorin  commence  to  rise  through  the  liquid,  indicating  that 
the  current  density  is  becoming  too  great.  This  is  remedied  by- 
placing  fresh  acid  upon  the  platinum  black  and  decreasing  the 
current. 

In  concentrating  the  solution  of  chlorplatinic  acid  prepared  in 
this  way,  chlorin  is  passed  through  it  for  a  short  while  to  in- 
sure freedom  from  platinous  compounds  in  case  any  have  been 
formed  during  the  electrolysis. 
19 


578  AGRICULTURAL  ANALYSIS 

THE  ESTIMATION  OF  POTASH  AS  PERCHLORATE 

.487.  General  Principles. — By  reason  of  the  great  cost  of  plat- 
inum chlorid,  analysts  have  sought  for  a  reagent  of  a  cheaper 
nature  and  yet  capable  of  forming  an  insoluble  compound  with 
potash.  Phosphomolybdic  and  perchloric  acids  are  the  reagents 
which  have  given  the  most  promising  results.55  The  principle  of 
the  method  with  the  latter  salt  is  based  on  the  insolubility  of  po- 
tassium perchlorate  in  strong  alcohol  containing  a  little  perchloric 
acid  and  the  comparative  easy  solubility  of  the  other  bases  usually 
associated  with  potassium  in  water.  The  French  chemists  have 
stated  that  magnesia,  when  present  in  considerable  quantities, 
interferes  with  the  accuracy  of  the  results.  Since  in  soil  analy- 
sis considerable  quantities  of  magnesia  are  often  found,  this  base, 
according  to  the  French  chemists,  should  previously  be  removed 
when  present  in  any  considerable  quantity,  by  the  process  de- 
scribed in  the  first  volume.  Kreider,  however,  as  will  be  seen 
further  on,  working  in  the  presence  of  magnesia,  did  not  notice 
any  disturbing  effects  caused  thereby.  The  method  is  applicable 
to  the  common  potash  salts  of  the  trade  and  with  certain  pre- 
cautions to  mixed  salts.  As  will  be  mentioned  later  on,  sulfuric 
acid  should  be  previously  removed  and  this  is  likely  to  intro- 
duce an  error  on  account  of  the  tendency  of  barium  sulfate  to 
entangle  particles  of  potash  among  its  molecules  and  thus  re- 
move them  from  solution.  The  barium  sulfate  should  be  pre- 
cipitated slowly  and  in  a  strongly  acid  (nitric  or  hydrochloric) 
solution.  The  loss,  which  is  inevitable,  is  thus  reduced  to  a 
minimum  and  does  not  seriously  affect  the  value  of  the  numbers 
found.  It  is  important  to  have  an  abundant  supply  of  pure  per- 
chloric acid,  and  as  this  is  not  readily  obtainable  in  the  market 
the  best  methods  of  preparing  it  are  given  below.  The  method, 
while  it  has  not  been  worked  out  extensively,  is  one  of  merit,  and 
seemingly  is  worthy  of  fair  trial  by  analysts.  The  process  is  by 
no  means  a  new  one,  but  was  first  proposed  by  Serullas,50  and 
prominently  called  to  the  attention  of  analysts  by  Schloesing,57 

55  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  2nd  Edition, 
1906,  1  :  414,  421. 

**  Annales  de  Chimie  et  de  Physique,  1831,  [2],  46  :  294. 
57  Comptes  rendus,  1871,  73  :  1269. 


SCHLOESING' s  MODIFICATION  OF  SERULLAS'  PROCESS    579 

Kraut,58  and  Bertrand.59  The  method  was  fully  developed  by  a 
committee  appointed  by  the  French  agricultural  chemists  in  iSS/.60 

Wense  has  also  described  an  improved  method  of  estimating 
potash  as  perchlorate  after  the  removal  of  sulfuric  acid  and  also 
a  process  of  preparing  perchloric  acid  by  distilling  potassium  per- 
chlorate with  sulfuric  acid  in  a  vacuum.61  He  was  also  the  first 
who  proposed  the  plan  of  rendering  potassium  perchlorate  in- 
soluble in  alcohol  by  dissolving  a  little  perchloric  acid  therein. 
The  best  approved  methods  now  known  of  preparing  the  per- 
chloric acid  and  conducting  the  analysis  will  be  described  in  the 
following  paragraphs. 

488.  Schloesing's  Modification  of  Serullas'  Process. — Dumas 
called  attention  to  certain  phenomena  which  took  place  at  Cher- 
bourg in  consequence  of  flooding  a  large  portion  of  land  with 
sea  water  as  a  means  of  defense  during  the  Franco-German  war 
and  the  effect  which  this  flooding  had  upon  subsequent  vegeta- 
tion.62 Peligot  was  also  interested  in  the  discussion.  Chevreul 
called  attention  to  the  difficulty  which  he  had  experienced  in 
determining  potash  and  soda,  or  rather  the  chlorids  of  potash 
and  soda,  by  means  of  platinum  chlorid. 

In  view  of  this  difficulty,  Schloesing  proposed  the  use  of 
perchloric  acid,  which  he  states  was  first  proposed  by 
Serullas  who  was  negligent  in  not  citing  in  his  paper 
the  data  of  analysis  which  are  the  most  efficacious  means  of 
determining  the  merits  of  a  method.03  The  chief  cause  of  the 
failure  of  the  method  proposed  by  Serullas  is  the  difficulty  of 
getting  perchloric  acid  in  sufficient  quantities  and  in 
a  pure  state.  To  Roscoe  is  awarded  the  credit  of  hav- 
ing devised  a  means  of  procuring  the  acid  in  abundance 
and  in  a  state  of  purity.  The  process  of  Serullas,  according  to 
Schloesing,  is  one  of  the  most  precise  when  pure  perchloric  acid 
furnished  by  the  perchlorate  of  ammonia  is  employed.  The 
method  proposed  for  conducting  the  analysis  is  as  follows:  In 

58  Zeitschrift  fiir  analytische  Chemie,  1875,  14  :  152. 

59  Moniteur  scientifique,  1881,  23  :  961. 

60  Grandeau,  Traite  d' analyse  des  matieres  agricoles,  3rd  Edition,  1897, 
1  :  419. 

61  Zeitschrift  fiir  angewandte  Chemie,  1891,  4  :  691  ;  1892,  5  :  253. 

62  Comptes  rendus,  1871,  73  :  1080. 

63  Comptes  rendus,  1871,  73  :  1269. 


AGRICULTURAL  ANALYSIS 

a  mixture  of  chlorids  or  nitrates  of  potash  and  soda  in  solution, 
perchloric  acid  is  added  and  the  mixture  evaporated  on  a  sand 
bath  until  it  is  almost  dry.  The  degagement  of  white  fumes  is  a 
sign  that  perchloric  acid  is  in  excess  and  that  the  formation  of 
the  salt  is  complete.  When  the  white  fumes  have  ceased  to  come 
over,  the  mass  is  cooled  and  the  perchlorate  of  potash  is  washed 
several  times  with  small  quantities  of  alcohol  of  36°.  The  more 
abundant  the  soda,  the  more  perchlorate  of  potash  is  retained  in 
its  crystals.  For  this  reason  it  is  advisable  to  dissolve  with  heat 
in  the  least  quantity  of  water  possible  the  perchlorates  when 
they  are  almost  washed,  and  to  evaporate  to  dryness.  Two  wash- 
ings with  alcohol  will  then  finish  the  purification  of  the  salt. 
With  a  few  drops  of  water  the  perchlorate  which  is  retained 
upon  the  filter  is  dissolved  and  received  into  a  capsule,  evap- 
orated again  to  dryness  and  heated  to  250°.  The  salt  is  then 
absolutely  dry  and  fit  to  weigh.  The  alcoholic  solution  of  per- 
chlorate of  soda  is  evaporated,  the  salt  is  afterwards  decomposed 
by  heat,  taken  up  by  water  and  evaporated  in  a  platinum  capsule. 
The  chlorid  of  soda  thus  obtained  very  often  contains  some  trace 
of  perchlorate.  In  order  to  have  an  exact  estimate  it  is  neces- 
sary to  transform  it  into  sulfate.  In  place  of  decomposing  the 
perchlorate  of  soda  by  heat,  it  may  be  treated  directly  by  sul- 
furic  acid. 

The  paper  gives  data  showing  the  exactitude  of  the  reaction 
and  describes  the  preparation  of  perchlorate  of  ammonia,  which  is 
the  reagent  employed  to  furnish  the  perchloric  acid. 

489.  Caspari's  Method  for  Preparing  Perchloric  Acid. — A 
hessian  crucible  about  15  centimeters  high  is  filled  with  moder- 
ately well  compressed  pure  potassium  chlorate  and  gradually 
Tieated  in  a  suitable  furnace  until  the  contents  become  fluid.64 
The  heat  must  then  be  carefully  regulated  to  avoid  loss  by  foam- 
ing due  to  the  evolution  of  oxygen.  The  heat  is  continued  until 
oxygen  is  no  longer  given  off  and  the  surface  of  the  liquid  be- 
comes encrusted,  which  will  take  place  in  from  one  and  a  half 
to  two  hours. 

After  cooling,  the  contents  of  the  crucible  are  pulverized  and 
**  Zeiischrift  fur  angewandte  Chemie,  1893,  6  :  68. 


CASPARI'S   METHOD  581 

heated,  with  vigorous  stirring,  to  boiling,  with  one  and  a  half 
times  their  weight  of  water.  By  this  process  the  potassium 
chlorid  which  has  formed  during  the  first  reaction  is  dissolved 
and  is  thus  removed.  The  residual  salt  is  washed  with  addi- 
tional quantities  of  cold  water  and  finally  dried.  To  remove  the 
potassium  base  from  the  crude  potassium  perchlorate  obtained  as 
above,  recourse  is  had  to  hydrofluosilicic  acid.  The  reaction  is 
represented  by  the  following  formula:  2KClO4-j-tI2SiF6— K2SiF6 
-|-HC1O4.  In  order  to  effect  this  decomposition  the  potassium 
perchlorate  is  dissolved  in  seven  times  its  weight  of  hot  water 
and  an  excess  of  hydrofluosilicic  added  to  the  boiling  solution. 
A  porcelain  dish  may  be  used.  The  boiling  is  continued,  with 
addition  of  water  to  compensate  for  evaporation,  for  about  an 
hour  until  particles  of  potassium  perchlorate  can  no  longer  be 
detected. 

On  cooling,  the  gelatinous  potassium  silicofluorid  is  deposited 
and  the  perchloric  acid  separated  therefrom  as  completely  as  pos- 
sible by  decantation.  The  residue  is  again  boiled  with  water  and 
a  little  hydrofluosilicic  acid  and  the  clear  liquor  thus  obtained 
added  to  the  first  lot.  The  second  boiling  may  generally  be  omit- 
ted. Finally,  any  residual  perchloric  acid  may  be  removed  on 
an  asbestos  felt  under  pressure.  The  clear  liquid  thus  obtained 
is  evaporated  on  a  steam-bath  to  the  greatest  possible  degree  of 
concentration  and  allowed  to  stand  in  a  cool  place  for  24  hours, 
whereby  is  effected  the  separation  of  any  remaining  potassium 
silicofluorid  or  potassium  perchlorate.  The  residual  liquid  when 
filtered  through  an  asbestos  felt  should  give  a  perfectly  clear  fil- 
trate. In  order  to  throw  out  the  last  traces  of  hydrofluosilicic 
acid  and  any  sulfuric  acid  present,  an  equal  volume  of  water  is 
added,  and  while  cold  small  quantities  of  barium  chlorid  are  suc- 
cessively added  until  the  barium  salt  is  present  in  a  very  slight 
excess.  The  clear  supernatant  liquid  is  poured  off  after  a  few 
hours  and  evaporated  until  the  acid  is  all  expelled  and  white 
fumes  of  perchloric  acid  are  noticed.  Any  potassium  perchlorate 
still  remaining  will  now  be  separated  and,  in  the  cold,  sodium 
perchlorate  will  also  be  separated  in  crystals.  The  clear  residue 
is  again  diluted  with  an  equal  volume  of  water  and  any  barium 


e&2  AGRICULTURAL  ANALYSIS 

salts  present  carefully  removed  with  sulfuric  acid.  The  mass  is 
allowed  to  stand  for  one  or  two  days,  and  is  then  filtered  through 
paper  and  is  ready  for  use.  The  removal  of  the  barium  with 
sulfuric  acid  may  be  omitted,  the  filtrate  being  diluted  with  an 
equal  volume  of  water  and  allowed  to  stand  for  one  or  two 
days  to  permit  the  deposition  of  the  last  traces  of  barium  silico- 
fluorid  and  barium  sulfate.  The  purity  of  the  acid  obtained  de- 
pends chiefly  on  the  purity  of  the  hydrofluosilicic  acid  at  first 
used.  Hence  to  get  good  results  this  acid  must  be  free  from 
foreign  bodies.  If  an  absolutely  pure  product  be  desired,  the 
acid  above  obtained  must  be  distilled  in  a  vacuum. 

490.  Method  of  Kreider. — Kreider  has  worked  out  a  sim- 
pler method  of  preparing  perchloric  acid  which  will  make  it  easy 
for  every  analyst  to  make  and  keep  a  supply  of  this  admirable 
yet  unappreciated  reagent.  This  method  is  conducted  as  fol- 
lows :05 

A  convenient  quantity  of  sodium  chlorate,  from  100  to  300 
grams,  is  melted  in  a  glass  retort  or  round-bottom  flask  and 
gradually  raised  to  a  temperature  at  which  oxygen  is  freely,  but 
not  too  rapidly  evolved,  and  kept  at  this  temperature  till  the 
fused  mass  thickens  throughout,  indicating  the  complete  con- 
version of  the  chlorate  to  the  chlorid  and  perchlorate,  which  re- 
quires from  one  and  one-half  to  two  hours;  or  the  retort  may 
be  connected  with  a  gasometer  and  the  end  of  the  reaction  deter- 
mined by  the  volume  of  oxygen  expelled,  according  to  the  equa- 
tion 

2NaClO8=NaCl+NaClO4+O2. 

The  product  thus  obtained  is  washed  from  the  retort  to  a  capa- 
cious evaporating  dish,  where  it  is  treated  with  sufficient  hydro- 
chloric acid  to  effect  the  complete  reduction  of  the  residual  chlo- 
rate, which,  if  the  ignition  has  been  carefully  conducted  with 
well  distributed  heat,  will  be  present  in  but  small  amount.  It  is 
then  evaporated  to  dryness  on  the  steam-bath,  or  more  quickly 
over  a  direct  flame,  and  with  but  little  attention  until  a  point 
near  to  dryness  has  been  reached,  when  stirring  will  be  found  of 
great  advantage  in  facilitating  the  volatilization  of  the  remaining 
65  American  Journal  of  Science,  1895,  149  :  443. 


METHOD  OF    KREIDER  583 

liquid  and  in  breaking  up  the  mass  of  salt.  Otherwise  the  per- 
chlorate  seems  to  solidify  with  a  certain  amount  of  water  and  its 
removal  from  the  dish,  without  moistening  and  reheating,  is  im- 
possible. 

After  triturating  the  residue,  easily  accomplished  in  a  porce- 
lain mortar,  an  excess  of  the  strongest  hydrochloric  acid  is  added 
to  the  dry  salt,  preferably  in  a  tall  beaker,  where  there  is  less 
surface  for  the  escape  of  hydrochloric  acid  and  from  which  the 
acid  can  be  decanted  without  disturbing  the  precipitated  chlorid. 
If  the  salt  has  been  reduced  to  a  very  fine  powder,  by  stirring 
energetically  for  a  minute,  the  hydrochloric  acid  will  set  free  the 
perchloric  acid  and  precipitate  the  sodium  as  chlorid,  which  in  a 
few  minutes  settles,  leaving  a  clear  solution  of  the  perchloric 
acid  with  the  excess  of  hydrochloric  acid.  The  clear  superna- 
tant liquid  is  then  decanted  upon  a  gooch,  through  which  it  may 
be  rapidly  drawn  with  the  aid  of  suction,  and  the  residue  re- 
treated with  the  strongest  hydrochloric  acid,  settled,  and  again 
decanted,  the  salt  being  finally  brought  upon  the  filter,  where  it 
is  washed  with  a  little  strong  hydrochloric  acid.  A  large  plati- 
num cone  will  be  found  more  convenient  than  the  crucible,  be- 
cause of  its  greater  capacity  and  filtering  surface.  When  the 
filter  will  not  hold  all  the  sodium  chlorid,  the  latter,  after  wash- 
ing, may  be  removed  by  water  or  by  mechanical  means,  with 
precautions  not  to  disturb  the  felt,  which  is  then  ready  for  the 
remainder.  Of  course,  if  water  is  used,  the  felt  had  better  be 
washed  with  a  little  strong  hydrochloric  acid  before  receiving 
another  portion  of  the  salt.  This  residue  will  be  found  to  con- 
tain only  an  inconsiderable  amount  of  perchlorate,  when  tested 
by  first  heating  to  expel  the  free  acid  and  then  treating  the  dry 
and  powdered  residue  with  97  per  cent,  alcohol,  which  dissolves 
the  perchlorate  of  sodium,  but  has  little  soluble  effect  on  the 
chlorid. 

The  filtrate,  containing  the  perchloric  acid  with  the  excess  of 
hydrochloric  acid  and  the  small  per  cent,  of  sodium  chlorid  which 
is  soluble  in  the  latter,  is  then  evaporated  over  the  steam-bath 
till  all  hydrochloric  acid  is  expelled  and  the  heavy  white  fumes 
of  perchloric  acid  appear,  when  it  is  ready  for  use  in  potassium 


584  AGRICULTURAL  ANALYSIS 

determinations.  Evidently  the  acid  will  not  be  chemically  pure, 
because  the  sodium  chlorid  is  not  absolutely  insoluble  in  hydro- 
chloric acid;  but  a  portion  tested  with  silver  nitrate  will  prove 
that  the  sodium,  together  with  any  other  bases  which  may  have 
gone  through  the  filter,  has  been  completely  converted  into  per- 
chlorate,  and  unless  the  original  chlorate  contained  some  potas- 
sium or  on  evaporation  the  acid  was  exposed  to  the  fumes  of 
ammonia,  the  residue  of  the  evaporation  of  a  portion  is  easily 
and  completely  soluble  in  97  per  cent,  alcohol,  and  its  presence 
is,  therefore,  unobjectionable.  One  cubic  centimeter  of  the  acid 
thus  obtained  gives  on  evaporation  a  residue  of  only  0.036  gram, 
which  is  completely  soluble  in  97  per  cent,  alcohol. 

Caspari's  acid  under  similar  treatment  gave  a  residue  in  one 
case  of  0.024  gram  and  in  another  0.047  gram.  If,  however,  a 
portion  of  pure  acid  be  required,  it  may  be  obtained  by  distilling 
this  product  under  diminished  pressure,  and,  as  Caspari  has 
shown,  without  great  loss,  providing  the  heat  is  regulated  ac- 
cording to  the  fumes  in  the  distilling  flask. 

Some  modification  of  the  above  treatment  will  be  found  neces- 
sary in  case  the  sodium  chlorate  contains  any  potassium  as  an 
impurity,  or  if  the  latter  has  been  introduced  from  the  vessel  in 
which  the  fusion  was  made.  In  these  circumstances  the  hydro- 
chloric acid  would  not  suffice  for  the  removal  of  potassium,  since 
a  trace  might  also  go  over  with  the  sodium,  and  thus  on  evap- 
oration a  residue  insoluble  in  97  per  cent,  alcohol  be  obtained. 
To  avoid  this  difficulty,  the  mixture  of  scdium  perchlorate  and 
chlorid,  after  treating  with  hydrochloric  acid  for  the  reduction 
of  the  residual  chlorate,  being  reduced  to  a  fine  powder,  is  well 
digested  with  97  per  cent,  alcohol,  which  dissolves  the  sodium 
perchlorate,  but  leaves  the  chlorid,  as  well  as  any  potassium  salt 
insoluble.  By  giving  the  alcohol  time  to  become  saturated,  which 
is  facilitated  by  stirring,  it  is  found  on  filtering  and  evaporating 
that  an  average  of  about  0.2  of  a  gram  of  sodium  perchlorate  is 
obtained  for  every  cubic  centimeter  of  alcohol  and  that  the  pro- 
duct thus  obtained  is  comparatively  free  of  chlorids,  until  the 
perchlorate  is  nearly  all  removed,  when  more  of  the  chlorid  seems 
to  dissolve.  This  treatment  with  alcohol  is  continued  until  on 


KEEPING  PROPERTIES  OF  PERCHLORIC  ACID  585 

evaporation  of  a  small  portion  of  the  latest  nitrate  only  a  small 
residue  is  found.  The  alcoholic  solution  of  the  perchlorate  is 
then  distilled  from  a  large  flask  until  the  perchlorate  begins  to 
crystallize,  when  the  heat  is  removed  and  the  contents  quickly 
emptied  into  an  evaporating  dish,  the  same  liquid  being  used  to 
wash  out  the  remaining  portions  of  the  salt.  When  the  distilla- 
tion is  terminated  at  the  point  indicated,  the  distillate  will  con- 
tain most  of  the  alcohol  employed,  but  in  a  somewhat  stronger 
solution, .so  that  it  requires  only  diluting  to  97  per  cent,  to  fit  it 
for  use  in  future  preparations.  The  salt  is  then  evaporated  to 
dryness  on  the  steam-bath  and  subsequently  treated  with  strong 
hydrochloric  acid  for  the  separation  of  the  perchloric  acid. 

One  cubic  centimeter  of  the  acid  prepared  in  this  way  on 
evaporation  gave  a  residue  in  one  case  of  0.0369  gram,  and  in 
another  0.0307  gram,  completely  soluble  in  97  per  cent,  alcohol. 
The  residue  was  then  ignited  and  the  chlorin  determined  by 
silver  from  which  the  equivalent  of  perchloric  acid  in  the  form 
of  salts  was  calculated  as  0.0305  gram.  By  neutralizing  the  acid 
with  sodium  carbonate,  evaporating,  igniting  in  an  atmosphere  of 
carbon  dioxid  till  decomposition  was  complete,  collecting  the 
oxygen  over  caustic  potash,  allowing  it  to 'act  on  hydriodic  acid 
by  intervention  of  nitric  oxid,  titrating  the  iodin  liberated  with 
standard  arsenic  and  calculating  the  equivalent  of  perchloric  acid, 
after  subtracting  the  amount  of  acid  found  in  the  form  of  salts, 
the  amount  of  free  perchloric  acid  per  cubic  centimeter  proved 
to  be  0.9831  gram. 

The  whole  process,  even  when  the  separation  with  alcohol  is 
necessary,  can  not  well  require  more  than  two  days,  and  during 
the  greater  part  of  that  time  the  work  proceeds  without  atten- 
tion. 

491.  Keeping  Properties  of  Perchloric  Acid. — By  most  author- 
ities it  is  asserted  that  perchloric  acid  is  a  very  unstable  body 
and  is  liable  to  decompose  with  explosive  violence  even  when 
kept  in  the  dark.  It  is  probable  that  this  tendency  to  spontaneous 
decomposition  has  been  exaggerated.  It  is  not  even  mentioned  by 
Gmelin.66 

66  Hand-Book  of  Chemistry,  Translated  by  Watts,  1859,  2  :  317. 


AGRICULTURAL   ANALYSIS 

The  most  concentrated  aqueous  acid  has  a  specific  gravity  of 
1.65,  is  colorless,  fumes  slightly  when  exposed  to  the  air,  and 
boils  at  200°.  It  has  no  odor,  possesses  an  oily  consistence  and 
has  a  strong  and  agreeably  acid  taste.  It  reddens  litmus  with- 
out bleaching  it  and  is  slowly  volatilized  at  138°  without  decom- 
position. It  is  unaffected  by  exposure  to  the  light,  even  the 
sun's  rays.  It  is  not  decomposed  by  hydrosulfuric,  sulfurous, 
or  hydrochloric  acids,  nor  by  alcohol.  Paper  saturated  with  the 
strong  acid  does  not  take  fire  spontaneously,  but  it  deflagrates 
with  red-hot  charcoal. 

The  acid  prepared  by  the  method  of  Kreider  has  approxi- 
mately the  composition  of  the  di-hydrate,  HC1O4.2H2O.  It  is 
usually  a  little  more  dilute  than  is  shown  by  the  above  formula. 
The  di-hydrate  is  quite  stable  and  the  more  dilute  acid  can  be 
kept  for  an  indefinite  time.  Kreider  has  kept  the  acid  for  six 
months  and  noticed  no  -change  whatever  in  its  composition.  Acid 
containing  one  gram  of  perchloric  acid  in  a  cubic  centimeter 
has  been  kept  three  months  with  perfect  safety.  There  is  no 
reason  why  the  strong  aqueous  acid  should  not  be  made  a  reg- 
ular article  of  commerce  by  dealers  in  chemical  supplies,  under 
proper  restrictions  for  storage  and  transportation. 

The  strong  acid  made  in  the  laboratory  of  the  Bureau  of 
Chemistry  by  the  Kreider  method  has  not  given  the  least  indi- 
cation of  easy  or  spontaneous  decomposition. 

492.  The  Analytical  Process. — The  perchlorate  process  can- 
not be  applied  in  the  presence  of  sulfuric  acid  or  dissolved  sul- 
fates.  This  acid,  when  present,  is  to  be  removed  by  the  usual 
methods  before  applying  the  perchloric  acid.  Phosphoric  acid 
may  be  present,  but  in  this  case  a  considerable  excess  of  the  re- 
agent must  be  used.  The  process,  as  originally  proposed  by  Cas- 
pari  and  carried  out  by  Kreider  is  as  follows  :OT 

The  substance,  free  from  sulfuric  acid,  is  evaporated  for  the 
expulsion  of  free  hydrochloric  acid,  the  residue  stirred  with  20 
cubic  centimeters  of  hot  water  and  then  treated  with  perchloric 
acid,  in  quantity  not  less  than  one  and  one-half  times  that  re- 
quired by  the  bases  present,  evaporated,  with  frequent  stirring, 
67  American  Journal  of  Science,  1895,  149  :  446. 


THE    ANALYTICAL    PROCESS  587 

to  a  thick,  sirup-like  consistency,  again  dissolved  in  hot  water 
and  evaporated,  with  continued  stirring,  till  all  hydrochloric  acid 
has  been  expelled  and  the  fumes  of  perchloric  acid  appear.  Fur- 
ther loss  of  perchloric  acid  is  to  be  compensated  for  by  addition 
of  more  of  the  reagent.  The  cold  mass  is  then  well  stirred  with 
about  20  cubic  centimeters  of  wash  alcohol  (97  per  cent,  alcohol 
containing  0.2  per  cent,  by  weight  of  pure  perchloric  acid);  with 
precautions  against  reducing  the  potassium  perchlorate  crystals 
to  too  fine  a  powder.  After  settling,  the  alcohol  is  decanted  on 
the  asbestos  filter  and  the  residue  similarly  treated  with  about  the 
same  amount  of  wash  alcohol,  settled,  and  again  decanted.  The 
residual  salt  is  then  deprived  of  alcohol  by  gently  heating,  dis- 
solved in  10  cubic  centimeters  of  hot  water  and  a  little  per- 
chloric acid,  when  it  is  evaporated  once  more,  with  stirring,  until 
fumes  of  perchloric  acid  rise.  It  is  then  washed  with  one  cubic 
centimeter  of  wash  alcohol,  transferred  to  the  asbestos,  preferably 
by  a  policeman  to  avoid  excessive  use  of  alcohol,  and  covered 
finally  with  pure  alcohol ;  the  whole  wash  process  requiring 
from  50  to  70  cubic  centimeters  of  alcohol.  It  is  then  dried  at 
about  130°  and  weighed. 

The  substitution  of  a  gooch  for  the  truncated  pipette  em- 
ployed by  Caspari  will  be  found  advantageous ;  and  asbestos 
capable  of  forming  a  close,  compact  felt  should  be  selected,  in- 
asmuch as  the  perchlorate  is  in  part  unavoidably  reduced,  during 
the  necessary  stirring,  to  so  fine  a  condition  that  it  tends  to  run 
through  the  filter  when  under  pressure.  A  special  felt  of  an  ex- 
cellent quality  of  asbestos  was  prepared  for  the  determinations 
given  below  and  seemed  to  hold  the  finer  particles  of  the  per- 
chlorate very  satisfactorily. 

A  number  of  determinations  were  made  of  potassium  chlorid 
unmixed  with  other  bases  or  non-volatile  acids  and  the  data  ob- 
tained are  recorded  in  the  following  table : 


Potassium 

Volume  of 

Potassium 

Error  on 

Error  on 

Error 

chlorid 

filtrate. 

perchlorate 

potassium 

potassium 

on 

used. 

Cubic  centi- 

found. 

perchlorate. 

chlorid. 

potash. 

Grams 

meters 

Grams 

Grams 

Grams 

Grams 

O.  IOOO 

54 

0.1851 

O.OOOS— 

0.0004  — 

0.0003  — 

O.  IOOO 

58 

0.1854 

0.0005  — 

O.OOO2  — 

O.OOO2  — 

O.IOOO 

51 

0.1859 

O.OOOO 

O.OOOO 

O.OOOO 

0.  IOOO 

50 

0.1854 

0.0005  — 

O.OOO2  — 

O.OOO2  — 

O.IOOO 

48 

0.1859 

O.OOOO 

O.OOOO 

O.OOOO 

O.IOOO 

52 

0.1854 

0.0005  — 

O.OOO2  — 

O.OOO2  — 

AGRICULTURAL   ANALYSIS 


Considerable  difficulty,  however,  was  experienced  in  obtaining 
satisfactory  determinations  of  potassium  associated  with  sulfuric 
and  phosphoric  acids.  As  Caspari  has  pointed  out,  the  sulfuric 
acid  must  be  removed  by  precipitation  as  barium  sulfate  before 
the  treatment  with  perchloric  acid  is  attempted,  and  unless  the 
precipitation  is  made  in  a  strongly  acid  solution,  some  potassium 
is  carried  down  with  the  barium.  Phosphoric  acid  need  not  be 
previously  removed,  but  to  secure  a  nearly  complete  separation 
of  this  acid  from  the  potassium,  a  considerable  excess  of  per- 
chloric acid  should  be  left  upon  the  potassium  perchlorate  before 
it  is  treated  with  the  alcohol.  When  these  conditions  are  care- 
fully complied  with,  fairly  good  results  may  justly  be  expected. 
Below  is  given  a  number  of  the  results  obtained : 


Compounds  used. 

Gram 

Potassium  chlorid=o.  10 
Calcium  carbonate=o.  13 
Magnesium  sulfate=o.  13 
Ferric  chlorid  =0.05 
Magnesium  sulfate=o.o5 
Manganese  dioxid=o.o5 
Sodium  phosphate=o.4o 

1  The  residue  showed  phosphoric  acid  plainly  when  tested. 

2  Only  traces  of  phosphoric  acid  found  in  the  residue. 

In  the  last  three  experiments  of  the  above  table  the  amount  of 
perchloric  acid  was  about  three  times  that  required  to  unite  with 
the  bases  present,  and  the  phosphoric  acid  subsequently  found 
with  the  potassium  was  hardly  enough  to  appreciably  affect  the 
weight,  although  its  absolute  removal  was  found  impossible. 

That  the  magnesia  does  not  produce  any  disturbing  effect,  as 
is  supposed  by  the  French  chemists,  Kreider  has  proved  by  the 
following  test :  One  hundred  and  fifty  milligrams  of  magnesium 
carbonate  were  treated  with  perchloric  acid,  evaporated  till 
fumes  of  perchloric  acid  appeared,  and  cooled,  when  the  mag- 
nesium perchlorate  crystallized:  But  on  treating  it  with  about 
15  cubic  centimeters  of  97  per  cent,  alcohol  containing  0.2  per 
cent,  of  perchloric  acid,  a  perfectly  clear  solution  was  obtained.  If 
therefore,  a  sufficient  excess  of  acid  be  used,  no  interference  will 
be  caused  by  the  presence  of  magnesium. 

While  it  is  true  that  the  potassium  perchlorate  obtained  may 


Volume 

Potassium 

Error  on 

Error 

of  filtrate. 

per- 

potassium 

on 

Error 

Cubic 

chlorate 

pei- 

potassium 

on 

centi- 

found. 

chlorate. 

chlorid. 

potash. 

meters. 

Grams 

Grams 

Grams 

Grams 

50 

0.1887 

0.0028-)- 

0.0014-)- 

0.0005+  l 

82 

0.1875 

0.0016+ 

O.OOC'8-(- 

0.0005  +1 

80 

0.  1861 

O.OOO2-J- 

o.oooi-j- 

O.OOOI-j-2 

80 

0.1843 

0.0016  — 

0.0008  — 

0.0005  —  2 

92 

0.1839 

O.OO2O  — 

O.OOIO  — 

0.0006  —  * 

60 

0.1854 

0.0005  — 

O.0002  — 

O.OOO2  —  * 

ESTIMATION  OF  POTASH  IN  CRUDE  POTASH  SAI/TS  589 

be  contaminated  with  a  trace  of  phosphoric  acid,  if  the  latter  be 
present  in  large  quantity  no  fear  of  contamination  with  mag- 
nesia need  be  entertained  if  a  sufficient  quantity  of  the  perchloric 
acid  be  used. 

493.  Removal   of  the   Sulfuric  Acid. — The     practical     objec- 
tion to  the  removal  of  the  sulfuric  acid  in  the  form  of  barium 
sulfate  rests  on -the  fact  of  the  mechanical  entanglement  of  some 
of  the  potash  in  the  barium  salt.     Unless  special  precautions  are 
observed  a  noticeable  amount  of  the  potash  will  be  found  with 
the  barium  sulfate. 

Caspari  has  succeeded  in  reducing  this  amount  to  a  minimum 
by  the  following  procedure:68  The  solution  of  barium  chlorid 
is  prepared  by  dissolving  127  grams  of  crystallized  barium  chlorid 
in  water,  adding  125  cubic  centimeters  of  35  per  cent,  hydro- 
chloric acid,  and  bringing  the  total  volume  up  to  one  liter  with 
water. 

Five  grams  of  the  substance  from  which  the  sulfuric  acid  is  to 
be  removed  are  boiled  with  150  cubic  centimeters  of  water  and 
20  of  strong  hydrochloric  acid.  While  the  solution  is  still  in 
ebullition  it  is  treated,  drop  by  drop,  with  constant  stirring,  with 
the  barium  chlorid  solution  above  mentioned,  until  a  slight  excess 
is  added.  This  excess  does  not  cause  any  inconvenience  subse- 
quently. After  the  precipitation  is  complete  the  boiling  is  con- 
tinued for  a  few  minutes,  the  mixture  cooled  and  made  up  to  a 
quarter  of  a  liter  with  water.  No  account  is  taken  of  the  vol- 
ume of  the  barium  sulfate  formed,  since,  even  with  the  precau- 
tions mentioned,  a  little  potassium  is  thrown  down  and  the  vol- 
ume of  the  barium  sulfate  tends  to  correct  this  error.  With  a: 
solution  from  which  the  sulfuric  acid  had  been  removed  as  above 
indicated,  Caspari  found  a  loss  of  only  one  milligram  of  potas- 
sium perchlorate  in  a  precipitate  weighing  over  800  milligrams. 

494.  Estimation  of  Potash  in   Crude  Potash   Salts   by  Means 
of  Perchloric  Acid. — The  potash  in  the  raw  salt  may  also  be 
determined  by  perchloric  acid  as  described  below.69  In  the  case  of 

88  Zeitschrift  fur  angewandte  Chemie,  1893,  6  :  73. 

69  Lunge,  Chemisch-technische  Untersucliungsmethoden,  5th  Edition, 
1904,  1  :  536. 


59O  AGRICULTURAL  ANALYSIS 

carnallit  or  bergkieserit  13.455  grams,  and  in  the  case  of  kainit, 
sylvinit  and  hartsalz  15.7225  grams  are  dissolved  in  about  300  cu- 
bic centimeters  of  water  with  15  cubic  centimeters  of  concen- 
trated hydrochloric  acid  in  a  500  cubic  centimeter  flask.  The 
solution  is  heated  to  the  boiling  point  and  the  sul- 
furic  acid  precipitated  by  barium  chlorid.  In  this  case 
a  slight  excess  of  barium  chlorid  is  without  any  hurtful 
influence  upon  the  exactness  of  the  process,  since  chlorid  of 
barium  is  converted  into  barium  perchlorid  by  the  perchloric  acid 
and  this  salt  is  easily  soluble  in  alcohol.  For  the  complete  pre- 
cipitation of  sulfuric  acid  there  are  required,  in  the  case  of  car- 
nallit, from  24  to  40  cubic  centimeters,  and,  in  the  case  of  kainit, 
from  65  to  80  cubic  centimeters  of  normal  barium  chlorid 
solution,  containing  122  grams  of  BaCl2,2H2O,  and  50  cubic 
centimeters  of  concentrated  hydrochloric  acid  in  one  liter.  After 
cooling,  the  flask  is  filled  to  the  mark  and  its  contents  filtered 
through  a  dry,  double  folded  filter  of  about  18  centimeters  diam- 
eter. When  filtered,  20  cubic  centimeters  are  evaporated  in  a 
flat,  dark-blue  glazed  porcelain  dish  of  about  10  centimeters 
diameter  with  five  cubic  centimeters  of  perchloric  acid  of  1.125 
specific  gravity  until  the  odor  of  hydrochloric  acid  has  disap- 
peared and  white  clouds  of  perchloric  acid  are  evolved.  The 
residue  is  treated  with  about  20  cubic  centimeters  of  96  per  cent, 
alcohol  and  carefully  rubbed  in  order  to  break  up  the  mass  into 
as  fine  particles  as  possible.  After  standing  for  a  short  time  the 
supernatant  liquid  is  filtered  through  a  filter  prepared  as  in  the 
platinum  method  given  above  or  through  a  gooch. 

The  rubbing  of  the  potassium  perchlorate  is  repeated  twice 
more,  but  not  with  pure  96  per  cent,  alcohol,  but  with  alcohol  to 
which  0.2  per  cent,  of  perchloric  acid  has  been  added.     Finally, 
in  order  to  remove  the  perchloric  acid,  the  filter  and  the  precipi- 
tate thereon  are  washed  with  a  spray  of  96  per  cent,  alcohol, 
using  as  little  thereof  as  possible  and  drying  and  weighing  as  in 
the  platinum  method.     In  this  process  one  milligram  of  potas-, 
sium   perchlorate,   corresponds   to  o.io  per  cent,   of   potassium., 
chlorate  or  of  potassium  sulfate  in  the  raw  material. 

495.  Influence  of  Carbonates. — In  the  method  of  determining 


INFLUENCE  OF  CARBONATES  591 

potash  by  perchloric  acid  Schenke  calls  attention  to  the  influence 
of  large  quantities  of  carbonate  of  lime  in  requiring  that  larger 
quantities  of  perchloric  acid  be  used  in  order  to  secure  complete 
transformation  of  the  lime  salts  into  perchlorate.  In  each  case 
it  is  necessary  that  such  a  quantity  be  used  that  the  addition  of 
additional  quantities  of  perchloric  acid  to  the  hot  concentrated 
filtrate  no  longer  gives  the  odor  of  hydrochloric  acid.70 

Further,  it  is  recommended  to  add  15  cubic  centimeters  of 
alcohol  to  the  warm  pasty  residue  obtained  upon  evaporation, 
since  the  solid  cooled  residue  is  very  incompletely,  or  at  least  dif- 
ficultly, soluble  in  alcohol.  If  the  material  under  investigation 
contains  large  amounts  of  lime  as  for  instance  marl,  residues 
from  filter  presses,  etc.,  it  is  advisable  to  separate  as  much  as 
possible  of  this  lime  from  the  solution  before  precipitating  the 
potash.  In  the  estimation  of  potash,  according  to  the  perchlo- 
rate method,  in  strongly  acid,  especially  sulfuric  acid,  solutions 
the  long  time  required  is  the  chief  objection.  In  such  cases  it 
is  quite  important  that  there  shall  be  two  evaporations  and  in- 
cinerations in  a  platinum  dish.  In  order  to  save  as  much  time 
as  possible,  the  process  is  carried  on  as  follows : 

Either  sulfuric  acid  or  fuming  nitric  acid  may  be  used  for  the 
solution.  The  solutions  are  evaporated  carefully  to  dryness  over 
a  small  free  flame,  and  thus  the  ammonium  salts  driven  off.  The 
residue  is  at  first  gently,  and  afterwards  gradually  more  strong- 
ly heated  until  a  distinct  red  heat  is  reached.  This  incineration 
does  not  need  to  be  carried  on  so  carefully  as  in  the  case  of 
heating  of  the  alkaline  chlorids,  since  the  alkaline  sulfates,  even 
when  kept  for  a  short  time  at  a  low  red  heat,  do  not  lose  any 
alkali.  The  ignited  sulfates  in  order  to  avoid  any  loss  in  con- 
sequence of  any  shrinking  on  cooling,  are  carefully  covered  and 
after  cooling  are  digested  with  hot  water  with  continued  rubbing 
and  with  a  little  hydrochloric  acid.  In  all  two  or  three  cubic 
centimeters,  of  a  five  per  cent,  solution  will  dissolve  all  soluble 
material.  The  contents  of  the  dish  are  then  washed  into  a  meas- 
uring flask  and  after  heating,  treated  with  a  slight  excess  of  a 
10  per  cent,  barium  chlorid  solution.  If  there  is  only  a  slight 
precipitate  of  barium  sulfate  the  separation  of  it  by  filtration 
70  Die  landwirtschaftlichen  Versuchs-Statiouen,  1908,  68  :  61. 


592  AGRICULTURAL  ANALYSIS 

may  be  omitted,  and  after  cooling  and  adding  a  few  drops  of  al- 
coholic phenolphthalein  solution  the  precipitation  of  the  phos- 
phate and  other  salts  is  accomplished  in  the  same  flask  by  means 
of  milk  of  lime,  free  of  alkali,  which  is  added  until  a  strong  red 
colored  saturated  solution  of  calcium  hydroxid  is  secured.  Milk 
of  lime  does  not  dissolve  the  barium  sulfate  and  the  filtrate  con- 
tains therefore  no  trace  of  sulfuric  acid.  After  standing  about 
half  an  hour  the  potash  is  determined  in  an  aliquot  part  of  the 
filtrate  after  acidifying  with  hydrochloric  acid  and  a  slight  con- 
centration thereof  on  the  water  bath  with  about  five  cubic  cen- 
timeters or  more  of  20  per  cent,  perchloric  acid. 

Finally,  special  attention  must  be  called  to  the  fact  that  on 
account  of  the  very  slight  solubility  of  barium  salts  in  alcohol 
only  a  very  small  excess  of  the  10  per  cent,  chlorid  of  barium 
solution  should  be  used  for  the  precipitation  of  the  sulfuric 
acid  and  only  about  two  cubic  centimeters  of  the  five 
per  cent,  hydrochloric  acid  should  be  used  for  the 
solution  of  the  ignited  salts  since  with  larger  quantities  of  hy- 
drochloric acid  more  milk  of  lime  is  necessary  for  saturation 
and  a  large  quantity  of  the  lime  salts  will  thus  be  incorporated 
in  the  precipitate  of  the  potassium  perchlorate. 

496.  Applicability  of  the  Process. — Experience  has  shown  that 
sulfuric  acid  is  the  only  substance  which  need  be  removed  from 
•ordinary  fertilizers  preparatory  to  the  estimation  of  the  potash 
•by  means  of  perchloric  acid.  The  fact  that  this  process  can  be 
used  in  the  presence  of  phosphoric  acid  is  a  matter  of  great  im- 
portance in  the  estimation  of  potash  in  fertilizers,  inasmuch  as 
these  fertilizers  nearly  always  contain  that  acid.  The  fact  that 
the  French  chemists  noticed  that  magnesia  was  a  disturbing  ele- 
rment  in  the  process,  as  has  been  indicated  in  volume  first,  proba- 
Ibly  arose  from  its  presence  as  sulfate.  Neither  Caspari  nor 
Kreider  has  noticed  any  disturbance  in  the  results  which  can  be 
traced  to  the  presence  of  magnesia  as  a  base. 

If  ammonia  be  present  there  is  a  tendency  to  the  produc- 
tion of  ammonium  perchlorate,  which  is  somewhat  insoluble  in 
the  alcohol  wash  used.  Solutions  containing  ammonia  before 
treating  by  the  perchlorate  method  for  potash  should  be  ren- 


ACCURACY  OF  THE  PROCESS  593 

dered  alkaline  by  soda-lye  and  boiled.  With  the  precautions 
above  mentioned,  the  method  promises  to  prove  of  great  value 
in  agricultural  analysis,  effecting  both  a  saving  of  time  and  ex- 
pense in  potash  determinations. 

497.  Accuracy  of  the  Process. — The  perchlorate  method  was 
tried  in  conjunction  with  the  platinum  method  on  the  two  samples 
of  potash  fertilizer  prepared  and  distributed  by  the  official  reporter 
on  potash  for  1893. 71  One  of  the  samples  was  of  a  fertilizer 
which  had  been  compounded  for  the  Florida  trade  and  contained 
bone,  dried  blood,  and  potash,  mostly  in  the  form  of  sulfate. 
The  other  sample  consisted  of  mixed  potash  salts,  sulfate,  chlo- 
rid,  double  salt,  kainit,  and  about  five  per  cent,  of  the  sulfates  of 
calcium,  potassium,  and  magnesium. 

The  results  obtained  by  Wagner  and  Caspari  on  the  two  sam- 
ples follow : 

Sample  No.  i.  Sample  No.  2. 

Per  cent,  potash          Per  cent,  potash 

By  the  platinum  method 13-25  37-98 

By  the  perchlorate  method i3-°9  37 -82 

In  transmitting  their  results  these  chemists  say :  "In  the  course 
of  our  work  the  fact  was  again  clearly  and  distinctly  brought  out 
that  the  improved  perchlorate  method  is  decidedly  superior  to  the 
old  platinum  chlorid  method  as  regards  rapid  execution  and  sim- 
plicity of  manipulation.  This  superiority  is  especially  perceptible 
in  the  analysis  of  mixed  fertilizers  containing  phosphoric  acid. 
For  this  reason  the  laborious  and  time-taking  separation  of  the 
alkalies,  which  is  necessary  in  the  .platinum  method,  is  entirely 
avoided."72  In  the  presence  of  organic  matter  containing  nitro- 
gen it  is  advisable  to  previously  destroy  the  nitrogenous  materials 
in  order  to  avoid  the  danger  of  their  transformation  into  am- 
monia during  the  progress  of  the  analysis. 

The  perchlorate  method,  on  the  whole,  appears  to  be  almost 
as  accurate  as  the  platinum  process,  requires  less  manipulation 
and  can  be  completed  in  a  shorter  time  and  at  less  expense  for 
reagents.     In  spite  of  these  advantages,  however,  the  use  of  the 
method  has  not  obtained  to  any  extent  in  this  country,  and  in  so 
far  as  the  author  knows,  is  not  employed  in  any  official  or  com- 
mercial laboratory  in  the  United  States. 
71  Division  of  Chemistry,  Bulletin  38,  1893  :  57. 
"  Division  of  Chemistry,  Bulletin  38,  1893  :  56. 


PART  FOURTH 


MISCELLANEOUS  FERTILIZERS  AND  INSECTICIDES 

498.  Classification. — Nitrogen,  phosphoric  acid,  and  potash  are 
the  most  important  of  the  plant  foods  both  from  a  commercial  and 
physiological  point  of  view.     They  are  the  chief  constituents  of 
the  most  important  fertilizers  and  manures,  but  are  by  no  means 
the  sole  essential  elements  of  plant  nutrition.     Lime,  magnesia, 
soda,  sulfur,  chlorin  and  many  other  elements  are  found  constant- 
ly in  plants  and  must  be  regarded  as  normal  constituents  there- 
of.    It  is  the  purpose  here,  however,  to  speak  only  of  those  sub- 
stances which  are  used  as  fertilizers  and  which  constantly  or  occa- 
sionally are  subjected  to  chemical  examination   for  determining 
their  commercial  or  agronomic  value.     These  bodies  may  be  con- 
veniently  divided   into  two  classes ;  viz.,   mineral  and  organic. 
Among  those  of  mineral  nature  may  be  mentioned  lime,  gypsum, 
marls,  wood  ashes,  common  salt,  and  ferrous  sulfate ;  among  those 
of  organic  nature  may  be  included  guano,  hen  manure,  stall  man- 
ure, composts,  and  muck  or  peat. 

499.  Forms  of  Lime. — By  the  term  lime  is  meant  the  prod- 
uct obtained  by  subjecting  limestone  or  other  lime  carbonates  to 
the  action  of  heat  until  the  carbon  dioxid  contained  therein  is 
expelled.     The  resulting  lime,  CaO,  when  exposed  for  some  time 
to  the  air,  or  at  once  on  the  addition  of  water,  is  converted  into 
the  hydrate  CaO2H2,  known  as  slaked  lime.     On  longer  exposure 
to  the  air,  the  hydrate  gradually  absorbs  carbon  dioxid  and  be- 
comes converted  into  carbonate.     In  whatever  form  lime  is  ap- 
plied to  the  soil,  it  is  found  in  the  end,  as  carbonate.     A  dis- 
tinction should  also  be  made  between  lime  obtained  from  min- 
eral  substances   and   that   got   from   organic    products   such    as 
shells.     Strictly  speaking  this  is  not  a  weighty  matter,  inasmuch 
as  limestones  are  sometimes  but  little  more  than  aggregations  of 
fossil  shells.     Practically,  the  distinction  is  made,  and  some  farm- 
ers prefer  shell  lime  to  that  of  any  other  kind.     Gas  lime,  that  is 


ACTION    OF    LIME  595 

lime  which  has  been  used  for  the  purification  of  illuminating  gas 
made  from  coal,  is  hardly  to  be  considered  in  this  connection, 
since  it  may  contain  very  little  even  of  the  hydrate.  In  this  case 
the  lime  has  been  converted  largely  into  carbonate  and  sulfid. 

500.  Application  of  Lime. — For  many  reasons  it  is  important 
that  the  lime  be  transported  to  the  field  before  it  has  had  time  to 
be  converted  into  hydrate.     The  transportation  costs  less  in  this 
state  and  it  can  be  handled  with  far  less  inconvenience  than  when 
slaked.     The  lime  should  be  placed  in  small  piles  and  left  thus, 
best  covered  with  a  little  earth,  until  thoroughly  slaked.     It  is 
then  spread  evenly  over  the  surface.     The  quantity  used  per  acre 
depends  largely  on  the  nature  of  the  soil.     Stiff  clays  and  sour 
marsh  lands  require  a  larger  dressing  than  loams  or  well  aerated 
soils.     From  three  to  six  thousand  pounds  per  acre  are  the  quan- 
tities usually  employed.     When  the  lime  is  once  thoroughly  incor- 
porated in  the  soil  it  is  rapidly  converted  into  carbonate,  but  while 
•n  the  caustic  state  it  may  act  vigorously  in  promoting  the  decay 
of  organic  matter  and  may  prove  injurious  in  promoting  the  de- 
composition of  ammonium  salts  with  attendant  loss  of  nitrogen. 

501.  Action  of  Lime. — The  benefits  arising  from  the  applica- 
tion of  lime  to  agricultural  lands,  although  in  many  cases  great, 
do  not  arise  from  any  distinct  fertilizing  action  of  its  own.  Plants 
need  lime  for  growth  and  need  plenty  of  it,  but,  as  a  rule,  any  soil 
which  is  good  enough  to  grow  crops  wrill  contain  enough  lime 
to  furnish  that  constituent  of  the  crops  for  many  years.     Its  ac- 
tion is  both  mechanical  and  chemical.     By  virtue  of  the  latter 
property  it  renders  available  for  plant  food  bodies  already  existing 
in  the  soil,  but  existing  in  such  shape  as  to  be  unavailable  for 
plants.     The  supply  of  plant  food  available  for  the  crops  of  one 
year  is  increased,  but  this  increase  is  at  the  expense  of  the  follow 
ing  years.     Lime  is  a  stimulant.     Theie  is  a  common  proverb 
that  "lime  enriches  the  father  but  beggars   the  son."     Never- 
theless, a  limestone  country  is  usually  a  fertile  one  and  soils  con- 
taining plenty  of  lime  naturally,  are  nearly  always  rich  soils.     It 
is  said  that  the  trees  and  plants  which  farmers  pick  out  as  indic- 
ative of  rich  land  are  nearly  always  those  which   prefer  lime 
soils. 


596  AGRICULTURAL   ANALYSIS 

The  mechanical  action  of  lime  on  soils  tends  to  lighten  heavy 
clays  and  loams  and  to  render  firmer  and  more  consistent  the 
light  and  shifting  sandy  soils.  When  a  lump  of  clay  is  stirred 
up  in  a  bucket  of  rain  water  the  water  becomes  muddy  and  re- 
mains that  way  for  many  days.  If,  however,  to  the  bucket  of 
muddy  water  a  little  lime  water  be  added  the  suspended  parti- 
cles of  clay  begin  to  flocculate  and  soon  the  water  is  clear  and  the 
clay  falls  to  the  bottom,  nor  does  it  again  make  the  water  muddy 
for  a  long  time  when  stirred  up  with  it.  The  flocky  character  of 
the  precipitate  is  tenaciously  retained  and  it  is  necessary  to 
knead  the  clay  for  some  time  to  induce  it  to  reassume  its  origi- 
nal heavy  character.  An  action  like  this  takes  place  when  lime 
is  added  to  heavy  soils  so  that  the  soil  becomes  more  porous  and 
assumes  a  better  tilth  on  cultivation.  With  sandy  soils  an  alto- 
gether different  action  takes  place.  In  making  mortar,  as  is  well- 
known,  sand  is  stirred  in  with  water  and  lime  and  after  being  ex- 
posed to  air  for  a  while  the  mixture  becomes  hard  and  firm, 
the  firmness  increasing  with  age.  This  is  due  to  the  fact  that 
when  the  mortar  dries  the  lime  begins  to  absorb  carbon  dioxid 
from  the  air  and  is  converted  into  grains  of  carbonate  which  ad- 
here strongly  to  neighboring  sand  grains  and  to  each  other  so 
that  the  whole  soon  gets  to  be  a  solid  mass.  Something  like 
this  takes  place  in  the  soil  and  the  sand  grains  are  to  some  ex- 
tent bound  together.  The  increased  firmness  of  the  soil  thus 
gained  is  often  of  considerable  advantage. 

Besides  these  actions,  which  are  more  or  less  mechanical,  lime 
exerts  a  chemical  action  on  many  soil  constituents.  Feldspar 
and  other  common  rocks  contain  potash,  and  this  potash  is  in 
such  a  form  as  to  be  inaccessible  to  plants.  These  rocks  exist  in 
the  shape  of  small  particles  in  many  soils  and  on  them  lime  exerts 
a  decomposing  action,  setting  the  potash  free.  Lime  also  hastens 
the  decomposition  of  the  nitrogenous  organic  matter  and  at  the 
same  time  renders  the  soil  more  retentive  of  the  products  formed. 
The  conversion  of  ammonia,  resulting  from  the  decomposition  of 
such  organic  matter  into  nitrites  and  nitrates,  is  not  easily  ac- 
complished without  a  proper  amount  of  calcium  carbonate.  The 
microorganisms  producing  this  change,  which  is  known  as  nitri- 


PREFERABLE  FORM   OF  LIME  597 

fication,  apparently  require  its  presence  for  neutralizing  the  acid 
formed.  In  general,  it  may  be  said  that  the  presence  of  lime 
hastens  the  destruction  of  organic  matter.  . 

It  is  difficult  to  say  just  what  soils  will  be  improved  by  liming 
and  what  will  not,  and  it  is  a  matter  which  must  be  settled  by 
experiment  in  each  case.  As  a  rule,  heavy  clays  and  loams  are 
benefited,  yet  of  two  such  soils,  apparently  identical,  one  may 
not  be  affected  in  any  marked  degree  while  the  other  may  readily 
respond  to  treatment.  Sandy  soils  are  often  improved  but  some- 
times not.  Sour,  boggy  lands,  are  usually  improved  by  the  ad- 
dition of  enough  lime  to  neutralize  their  undue  acidity.  Marsh 
grasses  and  plants  are  more  tolerant  of  acid  in  the  soil  than  tame 
grasses  are,  so  that  in  unlimed  soil  the  former  run  out  the  latter. 
The  application  of  lime  alone  to  a  very  poor  soil  does  not  pay. 

The  particles  of  lime  resting  in  the  soil  are  partially  dissolved 
by  the  next  rainfall  after  application,  or  by  the  soil  moisture, 
forming  lime  water,  and  the  lime  is  distributed  in  this  form 
through  the  soil  to  some  extent.  It  all  probably  soon  becomes 
converted  into  carbonate  as  ground  air  is  usually  quite  rich  in 
carbon  dioxid.  Indeed,  for  many  soils,  it  is  immaterial  whether 
lime  be  applied  as  lime  or  as  carbonate,  granting,  of  course,  that 
the  latter  be  ground  to  a  fine  powder.  Economy  is  in  favor  of 
the  lime,  however,  not  only  because  it  needs  no  grinding,  but 
because  it  is  lighter  than  the  corresponding  amount  of  carbonate, 
making  a  saving  in  transportation.  The  difference  is  quite  consid- 
erable, 56  pounds  of  lime  being  equivalent  in  effect  to  100  pounds 
of  carbonate.  For  these  reasons  as  well  as  because  it  possesses 
some  valuable  properties  not  shared  by  the  carbonate,  it  is  pro- 
bable that  for  most  localities  lime  is  to  be  preferred  to  any  form 
of  ground  oyster  shells,  ground  limestone,  marble  dust  or  the  like. 

One  of  these  valuable  properties  not  possessed  by  limestone,  is 
said  to  be  that  of  acting  as  a  fungicide  and  insecticide.  As  a 
rule,  fungi  prefer  acid  reaction  in  the  substances  in  which  they 
grow,  so  that  the  strongly  alkaline  properties  of  lime  may  make 
a  limed  soil  unsuitable  for  their  growth. 

502.  Preferable  Form  of  Lime. — Burned  lime  or  slaked  lime 
as  has  already  been  said,  is  to  be  preferred  to  lime  carbonate  where 


598  AGRICULTURAL  ANALYSIS 

quick  action  in  neutralizing  a  free  acid  or  aiding  in  decomposi- 
tion is  the  object  in  view.  In  a  soil  rich  in  ammonia  compounds 
the  powdered  lime  carbonate  is  preferable  in  order  to  avoid  loss 
of  the  nitrogen  compounds.  Burned  lime  also  exists  in  a  finer 
state  of  subdivision  than  is  usually  found  in  the  ground  rock 
or  shells.  If  the  final  effect  desired  is  the  amelioration  of  the  phys- 
ical state  of  the  soil  and  the  promotion  of  nitrification  there  is 
little  difference  in  value  between  the  burned  and  unburned  lime. 

503.  Analysis  of  Lime. — Lime,  which  is  prepared  for  use  as 
a  fertilizer  is  rarely  submitted  to  a   chemical  examination.     It 
it  is  easy  to  see,  however,  that  such  an  examination  is  of  some  im- 
portance. If  the  real  value  of  a  sample  be  dependent  on  the  con- 
tent of  lime,  the  actual  quantity  present  as  determined  by  analy- 
sis, must  fix  the  value  for  agricultural  purposes.     The  more  im- 
portant things  to  be  determined  are  the  quantities  of  lime,  and  of 
slaked  lime,  of  undecomposed  calcium  carbonate,  and  of  insoluble 
matter.     It  will  be  also  of  interest  to  determine  the  respective 
quantities  of  lime  present  as  oxid,  hydrate,  and  carbonate.     If  any 
question  be  raised  in  the  case  of  slaked  lime  in  respect  of  its 
origin,  it  can  usually  be  answered  by  an  examination  of  the  un- 
burned or  unslaked  residues.     In  perfectly  slaked  lime  containing 
no  debris,  the  analyst  will  be  unable  to  discover  whether  it  has 
been  made  from  limestone,  marble  or  shells.     The  lime  used  for 
agricultural  purposes  should  be  reasonably  free  of  magnesia,  and 
should  not  be  air-slaked  before  transportation  to  the  field.     In 
<lry  air-slaking,   a   considerable   quantity  of  carbonate   may  be 
formed. 

504.  The  Analytical  Process,     (i)  Insoluble  and  Soluble  Con- 
stituents.— A  representative  sample  of  the  lime  having  been  se- 
cured, it  is  reduced  to  a  powder  and  passed  through  a  half  milli- 
meter mesh  sieve  or  ground  to  a  fine  powder  in  an  agate  mortar. 
Two  grams  of  this  sample  are  digested  with  an  excess  of  hydro- 
chloric acid,  for  two  hours  with  frequent  stirring,  filtered,  the 
residue  washed  with  hot  distilled  water  until  chlorin  is  all  re- 
moved, and  dried  to  constant  weight.  The  lime,  magnesia,  silica, 


GYPSUM  OR  LAND  PLASTER  599 

and  other  constituents  of  the  filtrate,  are  determined  by  the  usual 
processes  of  mineral  analysis.73 

(2)  State  of  Combination  of  the  Lime. — In  a  lime  containing 
only  small  quantities  of  magnesia  the  lime  carbonate  may  be  de- 
termined by  estimating  the  carbon  dioxid  by  any  one  of  the  reli- 
able processes  in  use.74  In  every  case  sufficient  acid  must  be  em- 
ployed to  combine  with  all  the  bases  present.  Tartaric  or  hydro- 
chloric acid  may  be  used.  From  the  volume  or  weight  of  the 
carbon  dioxid  obtained  the  quantity  of  calcium  carbonate  may  be 
calculated.  Since  magnesium  carbonate  is  more  easily  decom- 
posed by  heat  than  the  corresponding  calcium  compound,  any 
residual  carbonate  in  a  well-burned  sample  is  probably  lime. 
The  total  percentage  of  lime  in  the  sample  is  to  be  determined 
in  the  usual  way  by  precipitation  as  oxalate  and  weighing  as 
carbonate  or  oxid.  The  lime  existing  as  oxid  can  be  determined 
by  exposing  a  weighed  sample  in  an  atmosphere  of  aqueous  vapor 
until  all  the  lime  is  slaked.  After  drying  at  100°  the  increase  in 
weight  is  determined  and  the  calcium  oxid  calculated  from  the 
formula,  CaO-f  H2O— CaO2H2. 

If  now  the  total  lime  be  represented  by  a;  the  lime  combined 
as  carbonate  by  b ;  and  that  present  as  oxid  by  c ;  the  quantity  x 
existing  as  hydrate  may  be  calculated  by  difference  from  the  equa- 
tion 

x=a — (b-\-c). 

The  total  lime  as  oxid  and  hydroxid  may  also  be  separated  from 
that  present  as  carbonate  by  solution  in  sugar.75  One  gram  of  cal- 
cium oxid  is  completely  soluble  in  150  cubic  centimeters  of  a  10 
per  cent,  sucrose  solution.  Magnesia,  iron  and  alumina  do  not 
interfere  with  the  determinations. 

5O5-  Gypsum  or  Land  Plaster. — This  substance  is  highly  prized 
as  a  top  dressing  for  grass  and  for  admixture  with  stall  manure 
for  the  purpose  of  fixing  ammonia.  Its  value  in  both  cases  de- 

73  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  2nd  Edition, 
1906,  1  :  402,  405,  434,  512. 

14  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  2nd  Edition > 
1906,  1  :  380,  436. 

75  Stone  and  Scheuch,  Journal  of  the  American  Chemical  Society,  1894,. 
16  :  721. 


6OO  AGRICULTURAL  ANALYSIS 

pends  upon  its  percentage  of  hydrated  calcium  sulfate.  The  quan- 
tity of  gypsum  of  all  kinds  mined  in  the  United  States  in  1906  was 
1,540,585.  short  tons.  Of  this  amount  only  62,671  short  tons 
were  sold  as  land  plaster.76  In  the  same  time  there  were  imported 
into  the  United  States  440,586  short  tons.  If  the  same  proportion- 
ate part  of  this  were  used  for  fertilizing  purposes,  it  may  be  said 
that  the  annual  consumption  of  land  piaster  in  the  United  States 
at  the  present  time  for  agricultural  uses  is  80,294  short  tons. 

Gypsum,  being  a  very  soft  mineral,  is  easily  ground  and  should 
be  in  the  state  of  a  fine  powder  when  used  for  fertilizing  purposes. 
It  is  soluble  in  about  500  parts  of  rain  water,  so  that  when  ap- 
plied as  a  top  dressing  it  is  carried  into  the  soil  by  rain.  Its 
favorable  action  is  both  as  a  plant  food  and  mechanically  in  modi- 
fying, in  an  advantageous,  way,  the  physical  constituents  of  the 
soil.  It  is  also  valuable  for  composting  and  for  use  in  stables 
by  reason  of  its  power  of  fixing  ammonia  by  the  formation  of 
lime  carbonate  and  ammonium  sulfate : 

( H4N )  ,CO3+CaSO4=  ( H4N )  2SO4+CaCO8. 

506.  Analysis  of  Gypsum. — For  agricultural  purposes  it  will 
be  sufficient  to  determine  the  quantity  of  sulfuric  acid,  and  to 
calculate  therefrom  the  amount  of  calcium  sulfate  in  the  sample : 
Or  the  lime  may  be  determined  and  the  quantity  of  sulfate  cal- 
culated therefrom. 

(1)  Insoluble  Matter. — In  the  conduct  of  the  work  the  sam- 
ple of  gypsum  is  rubbed  to  an  impalpable  powder  in  an  agate 
mortar.     The  sample,  about  one  gram,  is  dissolved  in  a  large 
excess  of  dilute  hydrochloric  acid,  the  digestion  being  contin- 
ued at  near  the  boiling-point,  with  frequent  stirring,  for  at  least 
two  hours.     The  solution  is  made  alkaline,  filtered,  and  the  resi- 
due washed  and  dried  to  constant  weight. 

(2)  Sulfuric  Acid. — The  washings  and  filtrate  from  the  above 
determination  are  made  up  to  a  definite  volume  with  water  and 
divided  into  two  equal  parts.     The  sulfuric  acid  is  estimated  in 
one  part  by  adding  to  it  sodium  carbonate  until  the  acidity  is 
nearly  neutralized.     The  sulfuric  acid  is  then  thrown  down  at 
near   boiling   temperature   by    the   gradual    addition   of   barium 

78  Burchard,  Mineral  Resources  of  the  United  States,  1906  :  1073. 


SOLUTION  IN  SODIUM  CARBONATE  6oi 

chlorid   solution.     The    barium    sulfate    formed    is    separated, 
washed,  dried,  and  weighed  in  the  usual  manner. 

(3)  Iron  and  Alumina. — To  the  other  half  of  the  solution  a 
little  nitric  acid  is  added  and  boiled  to  convert  any  ferrous  into 
ferric  iron.     On  the  addition  of  ammonia  the  iron  and  alumina 
are  separated  as  hydroxids,  collected  on  a  gooch,  washed,  dried, 
ignited,  and  weighed  as  oxids. 

(4)  Lime. — In  the  filtrate  the  lime  is  thrown  out  as  oxalate, 
and  separated  and  weighed  in  the  usual  way  as  oxid.     One  part 
of  CaO  is  equal  to  2.4286  parts  of  CaSO4. 

(5)  Moisture. — Two  grams  of  the  sample  are  dried  to  con- 
stant weight  at  80°. 

(6)  Water  of  Crystallization. — The  residue   from  the  above 
drying  is  heated  to  150°,  until  a  constant  weight  is  obtained.    The 
loss  represents  water  of  crystallization. 

(7)  Carbonates. — The  carbon  dioxid  is  evolved  by  the  usual 
process,  and  calculated  to  calcium  carbonate. 

507.  Solution  in  Sodium  Carbonate. — Gypsum  is  also  easily 
decomposed  by  boiling  with  a  solution  of  about  10  times  its 
weight  of  sodium  carbonate.  The  calcium,  by  this  operation,  is 
converted  into  carbonate  and  can  be  collected  on  a  gooch,  washed, 
and  estimated  as  usual,  but  in  this  case  it  will  contain  all  the 
insoluble  matters,  from  which  the  lime  can  be  separated  by  solu- 
tion in  hydrochloric  acid. 

In  the  filtrate  from  the  above  separation  the  excess  of  sodium 
carbonate  is  removed  by  the  addition  of  hydrochloric  to  slight 
acidity,  and  the  sulfuric  acid  estimated  as  described  in  the  pre- 
ceding paragraph. 

Pure  gypsum  has  a  composition  represented  by  the  follow- 
ing formula:  CaSO4.2H2O. 

It  contains: 

Per  cent. 

Sulfur  trioxid 46.51 

Lime 32.56 

Water 20.93 

A  commercial  sample  of  ordinary  gypsum  should  have  about 
the  following  composition  :77 

77  Frankland,  Agricultural  Chemical  Analysis,  1883  :  240. 


6O2  AGRICULTURAL  ANALYSIS 

Per  cent. 

CaSO4.2H,O 88.15 

CaCOj 3  50 

Fe2Os  and  A12O3 1.50 

Insoluble 2.80 

Organic  matter 0.50 

Water  and  undetermined 3.55 

Fine  ground  gypsum  in  the  arid  regions  of  the  United  States, 
especially  when  transported  during  the  hot  months,  loses  one 
molecule  of  its  crystal  water,  and  this  often  leads  to  disagree- 
ments respecting  weight.78 

Hilgard  also  calls  attention  to  the  fact  that  soils  naturally 
impregnated  with  gypsum  are  not  productive.  It  is,  however, 
very  useful  as  a  dressing  to  soils  containing  "black  alkali"  (car- 
bonate of  soda),  converting  the  carbonate  of  soda  into  sulfate, 
a  far  less  injurious  ingredient.  After  solution  in  water  it  pene- 
trates the  soil  and  effects  changes  in  its  zeolithic  constituents, 
setting  potash  free  and  thus  increasing  the  stores  of  plant  food.79 

508.  Common  Salt. — Common  salt  is  highly  esteemed  in  many 
quarters  as  a  top  dressing  for  lawns  and  meadows,  and  also  for 
cultivated  crops.  Its  action  is  chiefly  of  a  mechanical  and  cata- 
lytic nature,  since  it  does  not  form  a  notable  percentage  of  the 
mineral  food  of  plants.  On  account  of  its  affinity  for  moisture  it 
is  also  said  to  have  some  value  as  a  condenser  and  carrier  of  water 
in  times  of  drouth.  On  account  of  its  great  cheapness,  selling 
often  for  less  than  $10  a  ton,  its  use  in  moderate  quantity  en- 
tails no  great  expense.  Its  ability,  however,  to  pay  for  its  own 
use  in  the  increased  harvest  is  of  a  doubtful  character  when  it 
is  applied  at  a  cost  of  more  than  a  few  dollars  per  acre.  In  the 
chemical  examination  of  a  sample  of  common  salt  which  is  to  be 
used  as  a  fertilizer,  a  complete  analysis  is  rarely  necessary. 
When  desired  it  can  be  conducted  according  to  the  usual  methods 
of  mineral  analysis.  For  practical  purposes  the  moisture,  insol- 
uble matter,  magnesia  and  chlorin  should  be  determined  and  the 
quantity  of  sodium  chlorid  calculated  from  the  latter  number. 
Traces  of  iodin  or  bromin  which  may  be  present  are  of  no  con- 
sequence. 

18  Hilgard,  Letter  to  Author,  1907. 
"  Soils,  1906  :  43. 


GREEN    VITRIOL  603 

The  moisture  is  determined  by  drying  two  grams  of  the  well- 
mixed  and  finely  powdered  sample  to  constant  weight  at  100°. 
The  chlorin  is  obtained  by  precipitation  of  an  aliquot  part  of  a 
solution  of  the  salt  by  set  silver  nitrate,  using  potassium  chro- 
mate  as  indicator. 

In  the  determination  of  insoluble  matter  it  should  not  be  for- 
gotten that  a  little  gypsum  may  be  present,  and  this  should  be 
dissolved  by  rubbing  to  a  finer  powder  and  by  repeated  digestion 
in  water.  The  magnesia  and  lime  are  separated  and  determined 
in  the  usual  manner.  If  the  quantity  of  gypsum  present  be  suf- 
ficient to  warrant  it,  the  sulfuric  acid  may  be  separated  and 
weighed  in  the  manner  already  described.  Common  salt,  when 
present  in  the  soil  in  proportions  greater  than  o.i  per  cent.,  is 
injurious  to  vegetation.  The  presence  of  salt  in  any  greater 
quantities  in  a  soil  renders  it  barren.  In  Texas  the  irrigation  of 
rice  fields  with  slightly  brakish  water  has  had  the  effect  of  ren- 
dering the  fields  unfit  for  rice  growing.  Salt  is  often  used  to  kill 
weeds,  and  it  is  extremely  doubtful  if  its  use  as  a  fertilizer  is 
ever  really  indicated. 

509.  Green  Vitriol. — When  iron  is  used  as  a  fertilizer  it  is 
sometimes  applied  as  ferrous  sulfate.  The  value  of  iron  in  a 
soil  is  incontestable,  and  by  reason  of  the  fact  that  fertile  soils 
are  always  well  aerated,  the  iron  present  in  the  arable  layer  is 
found  in  the  ferric  state.  When  green  vitriol  is  applied  to  the  soil 
it  undergoes  gradual  oxidation  and  appears  finally  in  a  more 
highly  oxidized  form  as  ferric  hydrate.  Iron  acts  directly  on  the 
plant  in  promoting  the  development  of  the  chlorophyll  cells,  and 
is  also  found  in  almost  all  parts  of  the  vegetable  organism.  A  too 
great  quantity  of  ferrous  sulfate  is  destructive  of  plant  growth, 
in  which  respect  it  resembles  common  salt.  It  should,  therefore, 
be  applied  with  due  regard  to  the  dangers  which  might  arise 
from  an  excessive  quantity.  It  is  not  likely,  however,  that  when 
applied  in  a  finely  powdered  state  at  the  rate  of  from  one  to 
two  hundred  pounds  per  acre  it  would  ever  prove  poisonous  to 
vegetation. 

In  the  analysis  of  a  sample  of  green  vitriol  it  will  be  sufficient 
to  determine  the  moisture,  water  of  crystallization,  iron,  and 


604  AGRICULTURAL  ANALYSIS 

sulfuric  acid.  The  moisture  may  be  ascertained  by  drying  the 
finely  powdered  sample  over  sulfuric  acid  for  a  few  hours.  The 
water  of  crystallization  is  separated  by  exposing  the  sample  to  a 
temperature  of  285°  for  two  hours.  The  iron  may  be  determined 
by  oxidizing  to  the  ferrous  state  by  boiling  with  nitric  acid 
and  then  precipitating  with  ammonia,  and  proceeding  as  directed 
for  iron  analysis.  The  sulfuric  acid  is  separated  as  barium  sul- 
fate  and  determined  as  already  directed. 

510.  Pyrites. — The  existence  of  iron  pyrites  in  a  soil  in  any 
notable  quantity  is  injurious.  The  pyrites,  which  is  sulfid  of  iron, 
FeS2,  is  converted  into  copperas,  (ferrous  sulfate  or  green  vitriol) 
in  which  state  before  passing  to  a  state  of  higher  oxidation,  it  is 
quite  injurious.    Iron  pyrites  is  easily  recognized  by  its  crystalline 
form  and  golden  luster.    It  has  often  been  mistaken  for  gold,  and 
to  this  fact  is  due  its  common  name,  "fool's  gold."     It  often  oc- 
curs in  globular  masses  in  marls,  and  in  this  state  is  known  as 
"sulfur  balls."     When  heated,  pyrites  takes  fire  and  burns  with 
a  pale  blue  flame  (sulfur  flame),  and  the  iron  is  converted  into 
ferric  hydrate. 

511.  Stall  Manures. — There    are    no    definite    methods    to    be 
described  for  the  analysis  of  that  large  class  of  valuable  fertilizer 
produced  in  the  stable  and  pen,  and  which  collectively  may  be 
called  stall  manures.     The    methods    of    sampling  have  already 
been  described,  but  only  patience  and  tact  will  enable  the  col- 
lector to  get  a  fair  representation  of  the  whole  mass.80     These 
manures  are  a  mixture  of  urine,  excrement,  waste  fragments  of 
fodder,  and  the  bedding  used  for  the  animals.     With  them  may 
also  be  included  the  night  soil  and  waste  from  human  habita- 
tions and  the  garbage  fro'm  cities.     All  of  these  bodies  contain 
valuable  plant  foods,  and  the  phosphoric  acid,  potash,  and  nitro- 
gen therein  are  to  be  determined  by  the  methods  already  given 
for  these  bodies  when  they  occur  in,  or  are  mixed  with,  organic 
matter.     In  general,  stall  manures  are  found  to  have  a  higher 
manurial  value  than  is  indicated  by  the  amount  of  phosphorus, 
potash,  and  nitrogen  which  they  contain.     Through  them  there 

80  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  2nd  Edition, 
1908,  2  :  16. 


HEN    MANURE  605 

is  introduced  into  the  soil  large  quantities  of  humus  bodies 
whereby  the  physical  state  of  the  soil  is  profoundly  modified  and 
its  adaptability  to  the  growth  of  crops,  as  a  rule,  increased.  The 
addition  of  active  nitrifying  ferments  to  stall  manures  is  also  ad- 
vantageous, since  they  often  contain  active  denitrifying  organisms 
derived  from  straw  and  similar  sources  whose  activity  is  checked 
by  the  proper  treatment  to  secure  progressive  nitrification.  Stall 
manures,  however,  may  in  many  cases  prove  to  be  injurious  to 
a  crop,  as  for  instance,  when  they  are  applied  in  a  poorly  decom- 
posed state  and  in  a  season  deficient  in  moisture. 

It  is  essential,  therefore,  that  the  bedding  of  animals  be  in  a 
finely  divided  state,  whereby  not  only  are  the  absorptive  powers 
of  the  organic  matter  increased,  but  also  the  conditions  for  their 
speedy  decay  favored.  To  avoid  the  loss  of  ammonia  arising 
from  decomposing  urine,  it  is  advisable  to  compost  the  stall 
manure  with  gypsum  or  to  sprinkle  it  from  time  to  time  with 
oil  of  vitriol. 

In  the  analysis  the  moisture  may  be  estimated  by  drying  to 
constant  weight  at  100°  or  at  a  lower  temperature  in  a  vacuum. 
The  potash  and  phosphoric  acid  are  determined  as  usual,  with 
previous  careful  incineration,  and  the  nitrogen  secured  by  the 
moist  combustion  process. 

The  organic  matter  of  farmyard  manure  in  many  cases  exerts 
a  very  beneficial  effect  on  the  texture  of  the  soil,  and  in  addi- 
tion serves  as  a  source  of  humus,  which  still  further  improves 
fertility.  For  these  reasons  the  actual  returns  from  the  applica- 
tion of  such  manures-  are  often  much  greater  than  would  be 
expected  from  the  total  quantity  of  plant  food  which  they  con- 
tain. 

There  is  no  other  virtue  in  stall  manure  than  is  found  in  its 
content  of  plant  food  and  its  effects  on  soil  texture. 

512.  Hen  Manure. — This  fertilizing  substance  is  a  mixture 
of  the  excrement  of  the  fowl  yard  with  feathers,  dust,  and  other 
debris.  Measured  by  the  standard  applied  to  commercial  fer- 
tilizers, hen  manure  has  a  low  value.  As  in  the  case  of  other 
farm  manures,  however,  it  produces  effects  quite  out  of  propor- 
tion to  the  amount  of  ordinary  plant  foods  which  it  contains. 


606  AGRICULTURAL  ANALYSIS 

In  a  sample  examined  at  the  Connecticut  station  the  percentages 
of  its  chief  constituents  were  found  to  be  the  following:81 

Water 51.84 

Organic  and  volatile  matters 24.27 

Ash 23.89 

The  organic  matter  contained  0.6 1  per  cent,  of  nitrogen  as  am- 
monia and  the  ash  0.97  per  cent,  of  phosphoric  acid,  and  0.59  per 
cent,  of  potash,  all  calculated  to  the  original  weight  of  the  sam- 
ple. The  percentage  of  water  in  this  sample  is  undoubtedly 
higher  than  the  average,  so  that  it  can  hardly  be  taken  to  rep- 
resent the  true  composition  of  this  manure.  The  potash,  phos- 
phoric acid,  and  nitrogen  are  to  be  determined  by  some  one  of 
the  standard  methods  already  described,  the  two  former  after 
careful  incineration. 

513.  Guanos  and  Cave  Deposits. — The  principal  constituents 
of  value  in  these  deposits  are  nitrogen  and  phosphoric  acid.  The 
other  organic  matters  are  also  of  some  value,  but  have  no  com- 
mercial rating.  The  nitrogen  may  be  present  in  all  its  forms ; 
viz.,  organic,  ammoniacal,  amid,  and  nitric,  and  for  this  reason 
is  well  suited  not  only  to  supply  nourishment  to  the  plant  in  the 
earlier  stages  of  its  growth,  but  also  to  cater  to  its  later  wants. 
In  guano  deposits  in  caves,  due  usually  to  the  presence  of  bats, 
similar  forms  of  fertilizers  are  found  and  the  soluble  constituents 
due  to  decay  and  nitrification  are  protected  from  the  leaching  to 
which  they  would  be  subjected  in  the  open  air. 

In  some  localities  in  the  United  States  a  few  open  deposits  are 
found,  but  the  humidity  of  our  climate,  except  in  the  arid  regions 
of  the  West,  has  prevented  the  immense  open  deposits  of  guano 
that  characterize  some  of  the  arid  islands  of  the  Pacific  Ocean. 

Many  bat  guanos  examined  in  the  laboratory  of  the  Bureau 
of  Chemistry  have  been  found  to  contain  potash,  in  one  case 
1.78  per  cent.  It  is  suggested,  therefore,  that  the  analyst  do 
not  omit  to  examine  each  sample  qualitatively  for  this  substance 
and  to  determine  its  amount  when  indications  point  to  its  pres- 
ence in  weighable  proportions.  In  the  many  samples  of  bat 
guano  of  American  origin  which  have  been  analyzed  in  the  last 

81  Connecticut  Agricultural  Experiment  Station,  Annual  Report,  1888,  :: 
80. 


TOTAL  PHOSPHORIC  ACID  IN   GUANOS  607 

few  years,  some  very  rich  in  plant  food  have  been  found.  In 
one  instance  the  total  percentage  of  nitrogen  present  was  io.ii 
per  cent.  In  some  cases  the  phosphoric  acid  is  high,  but  rarely 
in  conjunction  with  a  high  content  of  nitrogen.  In  one  instance 
where  the  total  phosphoric  acid  reached  14.53  Per  cent.,  the  con- 
tent of  nitrogen  was  4.87  per  cent. 

In  respect  of  the  process  of  analysis  there  are  no  especial 
•directions  to  be  given.  The  phosphoric  acid  may  be  determined 
as  given  below,  and  the  potash  by  the  usual  methods.  The  total 
phosphoric  acid  and  potash  are  determined  only  after  the  destruc- 
tion of  the  organic  matter. 

In  old  cave  deposits  the  processes  of  decay  and  nitrification 
seem  to  have  long  been  completed  and  very  little  power  of  in- 
ducing nitrification  in  culture  solutions  seeded  from  these  sam- 
ples has  been  found. 

514.  French  Official  Method  for  Total  Phosphoric  Acid  in 
Guanos. — To  determine  the  phosphoric  acid  in  guanos,  the  meth- 
od officially  adopted  by  the  French  agricultural  chemists  may 
be  used.82 

Two  grams  of  the  sample  are  rubbed  up  in  a  porcelain  cruci- 
ble with  a  decigram  of  slaked  lime  to  prevent  the  possible  reduc- 
tion of  the  phosphoric  acid  by  the  organic  matter.  The  mixture 
is  slightly  moistened  with  a  few  drops  of  water,  dried  on  a  sand- 
bath,  and  afterwards  heated  to  redness,  best  in  a  muffle,  until 
organic  matter  is  destroyed.  The  contents  of  the  crucible  are 
detached  and  placed  in  a  flask  of  200  cubic  centimeters  capacity. 
The  crucible  is  well  digested  twice  with  some  hydrochloric  acid 
to  dissolve  any  adhering  fragments,  and  finally  washed  with  hot 
water,  the  acid  and  water  being  added  to  the  flask.  The  con- 
tents of  the  flask  are  boiled  for  15  minutes  and  then  poured 
into  a  flat-bottom  dish,  the  flask  well  rinsed  three  or  four  times 
with  small  quantities  of  water,  and  the  liquor  and  washings  evap- 
orated to  dryness  to  render  the  silica  insoluble.  The  residue  is 
taken  up  by  a  mixture  of  10  cubic  centimeters  each  of  hydro- 
chloric acid  and  water,  heated  for  a  few  minutes  and  filtered, 
and  the  dish  well  washed  with  successive  small  portions  of  water, 
82  Sidersky,  Analyse  des  Engrais,  1901  :  61. 


608  AGRICULTURAL  ANALYSIS 

but  the  total  volume  of  the  filtrate  and  washings  should  not  ex- 
ceed 80  cubic  centimeters.  In  this  filtrate  the  phosphoric  acid 
may  be  determined  by  any  one  of  the  approved  methods. 

515.  Waste  Leather. — This  material  belongs  probably  to  that 
class  of  nitrogenous  substances  which  has  a  small  immediate  value 
for  plant  nutrition.  The  chief  manurial  value  of  the  waste  is 
found  in  its  nitrogenous  content.  The  value  of  this  for  available 
plant  food  has  been  investigated  by  Lindsey.83  A  complete  resume 
of  the  literature  of  the  subject  is  also  given  by  him. 

A  good  way  of  identifying  leather  waste  is  by  the  process  pro- 
posed by  Dabney.84  It  depends  on  the  color  produced  in  a  solu- 
tion of  iron  phosphate  by  the  tannin  compounds  derived  from  the 
leather.  The  reagent  is  prepared  by  dissolving  a  freshly  made 
precipitate  of  iron  phosphate  from  10  grams  of  ferric  chlorid  in 
400  cubic  centimeters  of  an  aqueous  solution  of  40  grams  of 
glacial  phosphoric  acid.  A  gentle  heat  promotes  the  solution  of 
the  phosphate. 

In  the  case  of  a  fertilizer  supposed  to  contain  leather,  about  one 
gram  of  the  material  is  treated  with  30  cubic  centimeters  of  water 
and  a  few  drops  of  sulfuric  acid.  The  mixture  is  boiled  and 
poured  on  a  filter.  To  a  portion  of  the  filtrate  some  of  the  solu- 
tion of  iron  phosphate  is  added,  and  the  mixture  made  alkaline 
with  ammonia.  If  leather  be  present  in  the  sample,  a  purple  or 
wine  color  will  be  developed.  Lindsey  could  easily  detect  the 
leather  when  it  was  added  in  10  per  cent,  quantities  by  the  above 
method,  and  he  regards  this  method  as  superior  to  the  micro- 
scope, which  is  unreliable  in  the  case  of  finely  ground  material. 

•While  leather,  as  such,  decays  slowly,  and,  therefore,  is  not  at 
once  available  for  the  nourishment  of  plants,  it  acquires  greater 
utility  after  digestion  in  sulfuric  acid.  Artificial  digestion  ex- 
periments with  leather  previously  treated  with  sulfuric  acid  show 
that,  approximately,  70  per  cent,  of  the  nitrogen  pass  into  solu- 
tion. Such 'a  prepared  leather  has,  therefore,  an  available  co- 

85  Agricultural  Science,  1894,  8  :  49,  98. 

Massachusetts   Agricultural    Experiment    Station,    Twelfth    Annual 
Report  :  285. 

M  North  Carolina  Agricultural  Experiment  Station,  Bulletin  3. 


ANALYSIS   OF    WOOD  ASHES  609 

efficient  in  respect  of  nitrogen  not  much  inferior  to  most  organic 
bodies. 

In  comparative  trials  with  sodium  nitrate  it  was  demonstrated 
that  nitrogen  in  leather,  previously  dissolved  in  sulfuric  acid, 
has  a  rank  of  about  60  when  it  is  rated  at  100  in  the  soda  salt. 

For  the  estimation  of  the  nitrogen  in  leather  the  moist  com- 
bustion process  is  to  be  preferred. 

516.  Hair  and  Horn. — Waste  hair  and  horn  also  have  a  high  ni- 
trogen content,  and  in  certain  circumstances  this  may  become  valu- 
able for  manurial  purposes.     To  this  end,  however,  a  treatment 
similar  to  that  prescribed  for  leather  is  imperative.    In  the  nat- 
ural state,  hair  and  horn  decay  so  slowly  as  to  be  of  little  conse- 
quence for  plant  food  within  any  reasonable  time  in  so  far  as 
practical   agriculture  is   concerned.     The   preliminary   digestion 
of  these  substances  with  sulfuric  acid  brings  a  large  proportion 
of  their  nitrogen  within  reach  of  the  growing  crop. 

517.  Analysis  of  Wood  Ashes. — The  only  kinds  of  ashes  used 
extensively  for  manurial  purposes  are  those  derived  from  the 
burning  of  hard  woods.    The  ash  of  soft  woods,  such  as  the  pine, 
is  too  poor  in  plant  foods  to  warrant  its  transportation  to  any 
great  distance  for  manurial  purposes.     The  methods  of  incinera- 
tion of  organic  bodies  for  the  purpose  of  obtaining  and  estimat- 
ing their  mineral  contents  will  be  fully  discussed  in  the  third 
volume  of  this  work. 

It  is  important  in  ash  analysis  to  know  whether  there  be 
enough  of  iron  present  to  combine  with  all  the  phosphoric  acid. 
For  manurial  purposes  it  will  be  found  sufficient  to  determine 
the  percentages  of  potash  and  phosphoric  acid  alone.  For  hy- 
gienic purposes  it  is  advisable  to  examine  the  ash  qualitatively 
and,  if  necessary,  quantitatively  for  zinc,  lead,  copper,  boric  acid, 
and  other  bodies  of  a  similar  character  which  may  be  naturally 
present  in  the  ash,  or  may  have  been  added  to  the  organic  sub- 
stance from  which  it  was  prepared  for  preservation  or  other 
purposes.  The  methods  of  making  these  special  investigations 
will  be  discussed  in  the  succeeding  volume.  At  present  will  be 
given,  however,  not  only  the  methods  for  detecting  phosphoric 


6lO  AGRICULTURAL  ANALYSIS 

acid  and  potash,  but  also  for  a  complete  analysis  of  an  ash  in  so 
far  as  its  usual  constituents  are  concerned. 

518.  Carbon,  Sand,  and  Silica. — The  earlier  official  agricultural 
methods  prescribe  the  following  procedure  for  the  determina- 
tion of  the  unburned  carbon,  and  the  sand  and  silica:85 

Five  grams  of  the  ash  are  treated  in  a  beaker,  covered  with  a 
watch-glass  with  50  cubic  centimeters  of  hydrochloric  acid  of 
1.115  specific  gravity,  and  digested  on  the  water  bath  until  all 
effervescence  has  ceased.  The  cover  is  removed  and  the  liquid 
evaporated  to  complete  dryness  to  render  the  silica  insoluble. 
The  residue  is  moistened  with  two  or  three  cubic  centimeters  of 
hydrochloric  acid  and  taken  up  with  about  50  cubic  centimeters 
of  water,  allowed  to  stand  on  the  water  bath  a  few  minutes, 
filtered,  and  thoroughly  washed.  The  filtrate  and  washings  are 
made  up  to  a  quarter  of  a  liter  for  analysis.  The  residue  is 
washed  from  the  filter  into  a  platinum  dish  and  boiled  about 
five  minutes  with  20  cubic  centimeters  of  a  saturated  solution 
of  pure  sodium  carbonate ;  afterwards  a  few  drops  of  pure 
sodium  hydroxid  solution  are  added  and  the  liquid  allowed  to 
settle,  and  it  is  then  decanted  through  a  tared  gooch.  The  residue 
is  boiled  with  sodium  carbonate  solution  and  decanted  as  before, 
a  second  and  a  third  time,  and  finally  brought  upon  the  felt  and 
thoroughly  washed,  first  with  hot  water,  then  with  a  little  dilute 
hydrochloric  acid,  and  finally  with  hot  water  until  free  of  chlo- 
rids.  The  residue  in  the  gooch  is  dried  at  no0  to  constant 
weight,  giving  the  carbon  and  sand.  It  is  then  incinerated  and 
the  weight  of  the  sand  determined,  the  difference  giving  the 
carbon.  It  is  advisable  to  examine  the  sand  with  a  microscope 
to  determine  if  it  be  pure.  The  alkaline  filtrate  and  washings 
from  the  carbon  and  sand  are  acidified  with  hydrochloric,  evap- 
orated to  dryness,  and  the  silica  separated  and  determined  in 
the  usual  way. 

Instead  of  determining  soluble  silica  directly  from  the  sodium 
carbonate  solution,  as  above,  another  portion  of  the  ash  may  be 
treated  with  hydrochloric  acid  and  evaporated  to  dryness  as  be- 
fore described,  filtered  on  an  ordinary  filter,  washed,  burned. 
85  Division  of  Chemistry,  Bulletin  43,  1894  :  390. 


FERRIC  PHOSPHATE  AND  THE  ALKALINE  EARTHS  6ll 

and  weighed,  giving  the  weight  of  silica  plus  sand,  from  which 
the  weight  of  sand  is  deducted  to  obtain  soluble  silica.  It  is 
inadmissible  to  separate  the  soluble  silica  from  the  residue  after 
it  has  been  ignited. 

Instead  of  limiting  the  quantity  of  hydrochloric  acid  used  for 
moistening  the  dried  residue,  as  suggested  above  by  the  official 
chemists,  enough  should  be  employed  to  fully  saturate  the  mass. 
The  weight  of  pure  ash  is  obtained  by  subtracting  from  the 
weight  of  the  sample  used  the  sum  o-f  the  weights  of  carbon, 
sand,  and  carbon  dioxid. 

519.  Ferric  Phosphate  and  the  Alkaline  Earths. — The  ferric 
phosphate,  lime,  magnesia,  and  manganese  are  determined  in  an 
aliquot  part  of  the  first  hydrochloric  acid  solution  and  wash- 
ings obtained  above.  Fifty  or  TOO  cubic  centimeters  may  be 
used,  corresponding  to  one  or  two  grams  of  the  original  ash. 
The  accurately  measured  quantity  of  the  solution  is  carefully 
treated  with  ammonia  until  the  precipitate  formed  on  its  addi- 
tion becomes  permanent  on  shaking.  Ammonium  acetate  and 
acetic  acid  are  then  added  until  the  mixture  has  assumed  a 
strongly  acid  reaction.  The  separation  of  the  ferric  phosphate 
precipitate  is  promoted  by  gentle  warming,  and  it  is  separated 
by  filtration  without  unnecessary  delay.  If  the  precipitate  be 
not  large  the  sample  contains  no  manganese  and  alumina  in 
weighable  quantities,  and  if  the  filtrate  be  not  red,  the  precipi- 
tate is  washed  with  hot  water  containing  a  little  ammonium 
nitrate.  It  is  then  ignited  and  weighed  as  Fe2P2O8  and  the 
quantity  of  ferric  oxid  computed  therefrom.  If,  however,  the 
precipitate  be  large,  it  is  well  washed  as  above  and  then  dis- 
solved in  as  small  a  quantity  as  possible  of  hydrochloric  acid, 
and  the  solution  is  again  precipitated  as  above  by  the  addition 
of  ammonia,  ammonium  acetate,  and  acetic  acid.  The  ferric 
phosphate  obtained  by  the  second  precipitation  is  treated  exactly 
as  above  described. 

In  case,  however,  any  weighable  quantities  of  manganese  or 
alumina  are  present  it  will  not  do  to  weigh  the  precipitate  of 
ferric  phosphate  directly  even  after  a  second  precipitation.  Also 
if  the  filtrate  at  first  obtained  have  a  red  color,  the  precipitate 


6l2  AGRICULTURAL  ANALYSIS 

may  contain  basic  ferric  phosphate.  In  this  latter  case  it  should 
be  ignited  and  weighed,  then  dissolved  in  hydrochloric  acid  and 
the  ferric  oxid  estimated  in  the  solution  and  from  the  difference 
the  quantity  of  combined  phosphoric  acid  calculated. 

The  separation  of  the  iron  from  the  phosphoric  acid  may  be 
accomplished  by  adding  tartaric  acid  to  the  hydrochloric  acid 
solution  of  the  iron  phosphate  above  obtained  and  then  ammo- 
nium chlorid  and  ammonia.  The  mixture  is  placed  in  a  flask 
and  ammonium  sulfid  added.  The  flask  is  closed,  placed  in  a 
warm  place  and  allowed  to  stand  until  the  supernatant  liquid  is 
clear  and  of  a  pure  yellow  color  without  a  trace  of  green.  The 
iron  is  separated  by  filtration,  washed,  dissolved,  and  estimated 
in  the  usual  way. 

If  manganese  and  alumina  be  present  the  iron  and  manganese 
are  separated  from  the  phosphoric  acid  and  alumina  by  the  pro- 
cesses just  given  for  the  separation  of  iron  from  phosphoric  acid. 
In  the  filtrate  the  alumina  and  phosphoric  acid  are  separated  as 
follows:  The  filtrate  is  evaporated  in  a  platinum  dish  after  the 
addition  of  an  excess  of  pure  sodium  carbonate  until  no  ammo- 
nia is  set  free  by  a  further  addition  of  the  carbonate.  Some 
nitric  acid  is  then  added  and  the  evaporation  continued  to  dry- 
ness.  The  residue  is  fused  and  after  cooling  softened  with  water, 
washed  into  a  small  beaker,  some  hydrochloric  acid  added, 
warmed,  and  filtered.  Ammonia  is  added  until  the  reaction  is 
alkaline.  If  no  precipitate  be  produced  no  alumina  is  present.  In 
this  case  more  nitric  acid  is  added,  the  solution  again  evaporated 
and  the  phosphoric  acid  determined  by  the  usual  methods. 

In  case  a  precipitate  is  formed,  showing  the  presence  of  alu- 
mina, nitric  acid  is  added  until  the  precipitate  is  dissolved,  and 
then  in  slight  excess  and  after  evaporation  the  phosphoric  acid 
separated  by  molybdic  solution  and  determined  as  usual.  From 
the  filtrate  the  excess  of  molybdic  acid  is  removed  by  hydrogen 
sulfid  and  the  alumina  determined  in  the  filtrate :  Or  the  alumina 
may  be  determined  directly  in  the  hydrochloric  acid  solution  of 
the  melt  above  obtained  as  aluminum  phosphate  by  adding  so- 
dium phosphate,  ammonia  and  acetic  acid.  The  aluminum  phos- 
phate is  separated  by  filtration  and  determined  in  the  usual  man- 


MODIFIED    METHOD  613 

ner.     The  phosphoric  acid  is  then  determined  in  another  aliquot 
part  of  the  original  filtrate  from  the  first  solution  of  the  ash. 

Since  most  ashes  contain  an  excess  of  phosphoric  acid  above 
the  quantity  required  to  combine  with  the  iron  it  is  preferable  to 
proceed  as  described  in  the  next  paragraph. 

520.  Modified  Method. — The  principle  of  the  method  rests  on 
the  assumption  that  all  the  phosphoric  acid  may  be  removed 
from  the  solution  by  the  careful  addition  of  iron  chlorid.  Any 
excess  of  iron  is  then  removed  by  ammonium  acetate  and  the 
manganese,  lime,  and  magnesia  are  separated  in  the  filtrate.  The 
percentage  of  iron  is  determined  by  reduction  of  the  iron  in  an- 
other portion  of  the  solution  and  titration  with  potassium  per- 
manganate. The  process  as  conducted  by  McElroy  is  as  fol- 
lows :80 

Moisture. — If  the  ash  contain  much  carbon  the  water  is  best 
determined  by  drying  in  vacuo  to  avoid  oxidation. 

Sand,  Silica,  and  Carbon. — Place  a  portion  of  the  ash  in  a 
weighed  platinum  dish,  weigh,  and  cover  the  sample  with  hydro- 
chloric acid  of  1.115  specific  gravity.  Evaporate  to  dryness  on 
the  water  bath,  and  then  heat  for  15  minutes  at  105°  to  no8  in 
an  air  bath.  Repeat  the  treatment  with  acid  and  drying :  Finally 
cover  with  a  third  portion  of  acid  and  digest  on  the  water  bath 
for  an  hour  or  two.  Filter  into  a  weighed  gooch  and  wash  the 
residue  free  of  chlorids.  The  gooch  is  best  weighed  with  the  dish 
to  avoid  the  necessity  of  transferring  the  silica  which  may  adhere 
to  the  sides  of  the  former.  Dry  at  a  few  degrees  above  the  boil- 
ing temperature  of  water  and  weigh.  Where  the  ash  contains 
much  charcoal  the  drying  is  best  done  in  a  vacuum  at  from  60° 
to  70°.  The  increase  in  weight  found  represents  sand,  silica,  and 
carbon :  Burn  and  reweigh.  The  loss  is  carbon. 

Another  portion  of  ash  is  treated  as  before  except  that  it  is 
filtered  through  a  paper  filter.  The  filtrate  is  united  with  that  of 
the  previous  sample  in  a  graduated  flask.  When  the  washing  is 
completed  the  filter  is  placed  in  the  dish,  a  weak  solution  of 
caustic  soda  added,  and  the  mixture  heated  on  the  water  bath 
for  some  time.  Decant  while  hot  through  a  fresh  filter  and  re- 
86  Manuscript,  Unpublished. 


614  AGRICULTURAL  ANALYSIS 

treat  the  residue  in  the  dish  with  another  portion  of  alkali.  Finally 
wash  with  hot  water  till  the  alkaline  reaction  disappears,  then 
with  weak  hydrochloric  acid,  then  with  water  until  chlorids  dis- 
appear. The  washed  mass  on  the  filter  is  transferred  to  a  plati- 
num dish  and  ignited.  The  weight  obtained  represents  sand. 

Separation  of  Phosphoric  Acid. — The  united  filtrates  from  the 
two  determinations  are  placed  in  a  graduated  flask  and  made  up 
to  the  mark.  An  aliquot  portion  of  this  solution  representing 
half  a  gram  of  the  original  ash  or  any  other  convenient  quantity 
is  transferred  to  a  beaker  and  a  solution  of  ferric  chlorid  added 
until  ammonia  produces  a  brown  precipitate  in  the  mixture.  Neu- 
tralize with  ammonia  and  hydrochloric  acid  alternately  until  the 
liquid  is  as  little  acid  as  it  can  be  and  still  remain  clear.  Add 
from  10  to  20  cubic  centimeters  of  a  solution  of  sodium  ace- 
tate (1:10)  and  bring  to  a  boil.  The  liquid  should  be  quite 
dilute.  Filter  and  wash  free  of  chlorids  with  boiling  water  con- 
taining some  sodium  acetate. 

Manganese. — Make  the  filtrate  faintly  alkaline  with  ammonia 
and  add  ammonium  sulfid.  Any  manganese  sulfid  which  may 
form  is  separated  by  filtration,  treated  with  dilute  acetic  acid  and 
the  resulting  solution,  which  should  be  clear,  heated  to  boiling, 
nearly  neutralized  with  caustic  soda,  and  mixed  with  bromin 
water.  The  resultant  manganese  dioxid  is  to  be  filtered  into  a 
gooch,  ignited  and  weighed  as  Mn3O4. 

Lime. — Reacidify  the  filtrate  from  the  manganese  sulfid  with 
acetic  acid,  heat  to  boiling  and  add  ammonium  oxalate:  Allow 
to  stand  over  night,  filter  through  a  gooch  and  wash  with  water 
containing  acetic  acid.  The  calcium  oxalate  can  be  weighed  as 
such,  but  it  is  preferable  to  dry  thoroughly  and  then  heat  in  a 
small  bunsen  flame  until  a  change  can  be  noted  passing  over  the 
precipitate.  If  this  is  carefully  done  the  residue  will  be  calcium 
carbonate.  In  any  case,  the  result  is  to  be  checked  by  igniting 
over  the  blast-lamp  to  constant  weight  and  weighing  the  lime 
thus  obtained. 

Magnesia. — In  the  filtrate  the  magnesia  can  be  determined  by 
sodium  phosphate  in  the  usual  manner.  In  very  accurate  work 
the  calcium  oxalate  obtained  as  directed  above  can  be  dissolved 


MODIFIED    METHOD  615 

and  reprecipitated,  and  the  magnesia  in  the  filtrate  added  to  that 
in  the  first  filtrate. 

.  Iron. — For  iron  another  aliquot  portion  of  the  original  solution 
is  used,  acidified  with  sulfuric,  evaporated  to  drive  off  hydro- 
chloric acid,  rediluted  and  passed  through  the  Jones  reductor. 
The  filtrate  is  titrated  with  potassium  permanganate  solution  in 
the  usual  manner. 

Alkalies. — For  the  alkalies  another  aliquot  portion  is  precipi- 
tated while. hot  with  barium  chlorid  and  barium  hydrate,  filtered, 
and  ammonia  and  ammonium  carbonate  added  to  remove  the 
excess  of  barium  salt.  Refilter,  evaporate  to  dryness  in  a  plati- 
num dish,  and  ignite  gently  to  expel  all  ammonia  salts ;  repeat 
this  operation  after  taking  up  with  water  and  finally  heat  to 
constant  weight.  The  weight  obtained  represents  a  mixture 
of  potassium  and  sodium  chlorids,  with  usually  carbon  derived 
from  impurities  in  the  ammonia.  A  little  magnesia  is  often 
present.  The  potassium  is  estimated  by  means  of  platinum  solu- 
tion, and  the  potassium  chlorid  found  deducted  from  the  total 
weight  gives  the  sodium  chlorid.  The  carbon  is  usually  un- 
weighable,  though  it  often  looks  as  if  present  in  considerable 
quantity.  It  may  be  estimated,  however,  by  dissolving  the  mixed 
chlorids  in  weak  hydrochloric  acid  and  filtering  through  a  gooch 
before  making  the  potassium  estimation.  The  estimation  of  the 
magnesia  remaining  with  the  mixed  chlorids  may  be  effected  by 
evaporating  the  alcoholic  solution  remaining  after  the  precipita- 
tion of  the  potassium  to  dryness,  redissolving  in  water,  placing 
the  solution  in  a  flask  provided  with  gas  tubulures,  introducing 
hydrogen,  and  placing  in  the  sunlight.  The  platinum  is  soon  re- 
duced, leaving  the  liquid  colorless.  Heating  facilitates  the  re- 
action. Displace  the  hydrogen  by  a  current  of  carbon  dioxid, 
filter,  concentrate  the  solution  and  precipitate  the  magnesia  by 
sodium  phosphate  in  the  usual  manner. 

Phosphoric  Acid. — It  is  best  to  determine  the  phosphoric  acid 
directly  in  an  aliquot  part  of  the  first  filtrate  from  the  hydro- 
chloric acid  solution  of  the  ash  obtained  as  described  under  the 
determinations  of  sand,  silica  and  carbon.  When  there  is  not 
enough  of  the  material  for  this,  the  precipitate  of  ferric  phosphate 


6l6  AGRICULTURAL  ANALYSIS 

may  be  dissolved  and  the  phosphoric  acid  determined  after  sep- 
aration with  ammonium  molybdate. 

Sulfuric  Acid. — Fifty  cubic  centimeters  of  the  original  hydro- 
chloric acid  filtrate,  obtained  as  described  under  the  determina- 
tions of  sand,  silica  and  carbon,  are  heated  to  boiling,  and  the 
sulfuric  acid  thrown  out  by  the  gradual  addition  of  barium 
chlorid.  During  the  precipitation  the  mixture  is  kept  at  the  boil- 
ing temperature,  but  taken  from  trie  lamp  and  the  precipitate 
allowed  to  settle  from  time  to  time  until  it  is  seen  that  an  addi- 
tional drop  of  the  reagent  causes  no  further  precipitate.  The 
barium  sulfate  is  collected,  dried,  and  weighed  in  the  usual  man- 
ner. 

Chlorin. — Dissolve  from  one  to  five  grams  of  the'  ash  in  nitric 
acid  in  very  slight  excess,  or  in  water.  If  the  solution  be  made 
in  nitric  acid  the  excess  must  be  neutralized  if  the  chldrin  be  de- 
termined volumetrically ;  and  if  the  solution  be  in  water,  nitric 
acid  must  be  added  if  the  determination  be  gravimetric. 

The  volumetric  determination  is  accomplished  in  the  usual 
manner  with  a  standard  silver  nitrate  solution,  using  potassium 
chromate  as  indicator.  The  gravimetric  determination  is  effected 
by  precipitation  with  silver  nitrate,  collecting,  washing,  and  dry- 
ing at  150°  the  silver  chlorid  obtained. 

Carbon  Dioxid. — The  carbon  dioxid  is  most  conveniently  esti- 
mated in  from  one  to  five  grams  of  the  ash,  according  to  its  rich- 
ness in  carbonates,  by  the  apparatus  described  in  Volume  I  or 
some  similar  device.87 

521.  Early  Official  Method  for  Determinations  of  the  Alkalies. 
— Evaporate  the  filtrate  and  washings  from  the  sulfuric  acid  de- 
termination, paragraph  519  in  a  porcelain  dish  to  dryness,  re-dis- 
solve in  about  50  cubic  centimeters  of  water  and  add  milk  of  lime, 
or  barium  hydroxid  solution,  which  must  be  perfectly  free  from 
alkalies,  until  no  further  precipitation  is  produced,  and  it  is  evi- 
dent there  is  an  excess  of  calcium  hydroxid  or  barium  hydroxid 
present ;  boil  for  two  or  three  minutes,  filter  hot,  and  wash  thor- 
oughly with  boiling  water,  precipitate  the  lime  and  baryta  from 

87  Wiley,  Principles  and  Practice  of  Agricultural  Analysis,  and  Edition, 
1906,  1  :  380. 


the  filtrate  with  ammonia  and  ammonium  carbonate,  filter,  evap- 
orate the  filtrate  to  dryness  in  a  porcelain  dish,  and  drive  off  the 
ammonia  salts  by  heat  below  redness.88  When  cold,  re-dissolve  in 
15  or  20  cubic  centimeters  of  water,  precipitate  again  with  a  few' 
drops  of  ammonia  and  ammonium  carbonate  solution,  let  stand  a 
few  minutes  on  the  water  bath  and  filter  into  a  tared  platinum 
dish  and  evaporate  to  dryness,  expel  the  ammonia  salts  by  heat- 
ing to  just  preceptible  dull  redness,  weigh  the  potassium  and  so- 
dium chlorids  obtained  and  determine  the  potassium  chlorid  with 
platinic  chlorid  as  usual. 

The  potassium  may  also  be  determined  by  the  perchlorate  meth- 
od, or  the  total  chlorin  be  determined  volumetrically,  and  the 
relative  percentages  of  potassium  and  sodium  chlorids  calculated 
by  the  usual  formula :  Or  multiply  the  weight  of  chlorin  in  the 
mixture  by  2.1035,  deduct  from  the  product  the  total  weight  of 
the  chlorids  and  multiply  the  remainder  by  3.6358.  The  product 
expresses  the  weight  of  the  sodium  chlorid  contained  in  the  mixed 
salts.  The  indirect  method  is  only  applicable  when  there  are  con- 
siderable quantities  of  alkalies  present  and  where  they  exist  in 
approximately  molecular  proportions.  It  is,  therefore,  a  process 
rarely  to  be  recommended  in  ash  analysis. 

522.  Latest  Official  Methods  for  the  Determination  of  Inor- 
ganic Plant  Constituents.89 — i.  Preparation  of  Sample. — The  ma- 
terial must  be  thoroughly  cleaned  from  all  foreign  matter,  es- 
pecially from  adhering  soil.  It  is  to  be  ground  and  preserved  in 
carefully  stoppered  bottles. 

2.  Determination  of  Carbon-Free  Ash.  (a)  Preparation  of 
calcium  acetate. — Dissolve  20  grams  of  pure  calcium  carbonate 
in  pure  acetic  acid,  and  dilute  to  one  liter.  Evaporate  20  cubic 
centimeters  of  the  solution  in  a  platinum  dish,  ignite  gently,  then 
strongly,  to  constant  weight.  The  dish  must  be  weighed  quickly. 
This  gives  the  calcium  oxid  in  20  cubic  centimeters. 

(a')  Alternative  Method. — Dissolve  marble  in  hydrochloric 
acid,  evaporate,  and  dry  to  render  silica  insoluble,  dissolve  with 
water  and  a  little  acid,  and  precipitate  iron  and  aluminum  in  the 

88  Division  of  Chemistry,  Bulletin  43,  1894  :  391. 

89  Bureau  of  Chemistry,  Bulletin  107,  1907  :  21. 


6l8  AGRICULTURAL  ANALYSIS 

usual  way.  The  calcium  is  then  precipitated  with  ammonia  and 
ammonium  oxalate  in  hot  solution,  the  precipitate  washed  well, 
dried,  ignited  and  weighed.  It  is  then  dissolved  and  diluted 
so  that  100  cubic  centimeters  contain  i.i  grams  calcium  oxid. 

It  is  best  to  test  the  purity  of  this  reagent  by  making  blank 
determinations  with  it. 

(b)  Preparation  of  Ash. — Moisten  from  10  to  20  grams  of  the 
substance  with  40  cubic  centimeters  of  calcium  acetate  solution, 
dry  on  a  water  bath,  and  ignite,  gently  at  first,  then  more  vigor- 
ously.    The  quantity  of  calcium  acetate  used  should  be  sufficient 
to  prevent  fusion  of  the  ash.     Some  form  of  apparatus  must  be 
used  to  prevent  volatilization,  either  Shuttleworth's  or  Tucker's, 
or  an  ordinary  platinum  dish  may  be  ir,ed,  fitted  with  a  cover,  like 
that  described  by  Wislicenus.     The  weight  of  the  ash  must  be 
corrected  for  lime,  carbon  dioxid  and  carbon. 

(c)  Determination  of  Carbon  Dioxid. — Using  the  ash  prepared 
in  (b),  liberate  the  carbon  dioxid  with  hydrochloric  acid  in  any 
of  the  usual  forms  of  apparatus,  determining  the  carbon  dioxid 
evolved  either  by  increase  of  weight  of  potash  bulbs  or  loss  of 
weight  of  the  apparatus.     The  former  method  is  preferred. 

(d)  Determination  of  Carbon,  Sand  and  Silica. — The  residue 
from  the  carbon  dioxid  determination  is  transferred  to  a  beaker 
or  evaporating  dish,  evaporated  to  dryness  and  thoroughly  dried 
and  pulverized  to  render  silica   insoluble.     The   dry  residue   is 
moistened  with  from  five  to  10  cubic  centimeters  of  hydrochloric 
acid,  taken  up  with  about  50  cubic  centimeters  of  water,  allowed 
to  stand  on  the  water  bath  for  a  few  minutes,  filtered  through  a 
parchment-paper  filter  (S.  and  S.  "hardened"  filters),  and  thor- 
oughly washed.     The  solution  and  washings  are  to  be  made  up  to 
250  cubic  centimeters  or  other  convenient  volume  and  preserved 
for  analysis.     This  is  solution  A. 

The  residue  is  washed  from  the  filter  (which  may 
be  used  again)  into  a  platinum  dish  and  boiled  about 
five  minutes  with  20  cubic  centimeters  of  a  saturated  solution 
of  pure  sodium  carbonate,  a  few  drops  of  pure  sodium  hydroxid 
solution  are  added,  the  solids  are  allowed  to  settle,  and  the  liquor 
decanted  through  a  tared  gooch.  The  residue  in  the  dish  is  boiled 


DETERMINATION    OF     INORGANIC     PLANT    CONSTITUENTS      619 

with  sodium  carbonate  solution  and  decanted  as  before,  and  the 
process  repeated  a  third  time,  after  which  the  residue  is  brought 
upon  the  filter  and  thoroughly  washed,  first  with  hot  water,  then 
with  a  little  dilute  hydrochloric  acid,  and  finally  with  hot  water 
until  free  from  chlorids.  The  gooch  and  contents  are  dried  to 
constant  weight  at  no",  and  the  combined  weight  of  carbon  and 
sand  determined.  After  incineration  the  loss  in  weight  gives  the 
carbon.  It  is  advisable  to  examine  the  residue  under  the  micro- 
scope to  ascertain  if  it  is  really  sand.  The  alkaline  filtrates  and 
washings  are  to  be  united,  acidified  with  hydrochloric  acid, 
evaporated  to  dryness,  and  the  silica  separated  and  determined 
in  the  usual  way. 

Alternate  Method. — Instead  of  determining  directly  the 
silica  dissolved  by  the  sodium  carbonate  solution,  as  described 
above,  another  portion  of  the  ash  may  be  treated  as  in  2(0}  and 
(rf),  and  the  residue  of  silica,  sand,  and  carbon  filtered  on  an  or- 
dinary filter,  washed,  burned,  and  weighed,  giving  the  combined 
weight  of  silica  and  sand,  from  which  the  weight  of  sand  found  in 
2(d)  is  to  be  deducted  to  obtain  the  silica.  It  is  inadmissable  to 
separate  the  soluble  silica  from  the  residue  after  ignition. 

Subtract  carbon,  carbon  dioxid,  and  calcium  oxid  added  in  the 
form  of  calcium  acetate  from  the  ash,  and  calculate  results  as 
carbon-free  ash. 

3.  Determination  of  Manganese,  Calcium,  and  Magnesium. — 
To  an  aliquot  of  solution  A,  corresponding  to  from  0.5  to  two 
grams  of  ash,  add  a  quantity  of  pure  ferric  chlorid  solution,  more 
than  equivalent  to  the  phosphoric  acid  which  may  be  present, 
neutralize  with  ammonia,  dissolve  the  precipitate  in  a  very  slight 
excess  of  hydrochloric  acid,  add  one  or  two  grams  of  sodium 
acetate  and  boil  one  or  two  minutes,  filter  at  once  and  wash  with 
boiling  water.  If  necessary,  dissolve  the  precipitate  in  hydro- 
chloric acid  and  reprecipitate  as  above.  Evaporate  the  filtrate 
and  washings  to  about  50  cubic  centimeters  and  determine  man- 
ganese, calcium,  and  magnesium  as  in  the  analysis  of  soils.90 
The  quantity  of  calcium  found  must  be  corrected  for  the  calcium 
.added. 

90  Bureau  of  Chemistry,  Bulletin  107,  1904  :  15,  (c),  (d),  (e). 


62O  AGRICULTURAL  ANALYSIS 

4.  Determination  of  Phosphoric  Acid. —  (a)  In  an  aliquot  por- 
tion of  the  hydrochloric  acid  solution,  corresponding  to  0.2  to  one 
gram  of  ash,  determine  the  phosphoric  acid  by  any  of  the  me- 
thods described  for  total  phosphoric  acid  in  fertilizers. 

(b)  The  determination  can  also  be  made  directly  in  the  plant 
substances  after  incineration  as  prescribed  in  the  methods  for 
phosphoric  acid,  in  fertilizers  using  sufficient  material  to  give  from 
0.2  to  one  gram  ash  in  the  aliquot  portion  of  the  solution  used 
for  the  phosphoric  acid  determination. 

5.  Determination  of  Sulfuric  Acid. —  Heat  an  aliquot  of  solu- 
tion A,  corresponding  to  from  0.5  to  one  gram  of  ash,  to  boiling 
and  add  barium  chlorid  solution  in  small  quantities  until  no  fur- 
ther precipitation  is  produced,  and  proceed  in  the  usual  manner 
to  determine  the  barium  sulfate. 

6.  Determination  of  Chlorin. — Determine  the  chlorin  as  silver 
chlorid,  either  gravimetrically  or  by  one  of  the  standard  volumet- 
ric processes,  in  a  nitric  acid  or  aqueous  solution  of  the  ash.  Ni- 
tric acid  may  be  used  as  the  solvent  in  2  (c)  and  the  solution  em- 
ployed for  this  purpose. 

7.  Potassium  in  Plants. — Potash  may  be  determined  as  directed 
under  fertilizers  for  potash  in  organic  compounds,  using  suf- 
ficient plant  material  to  get  from  0.5  to  one  gram  ash  in  the  ali- 
quot portion  of  the  solution  used  for  the  potash  determination. 

8.  Sulfur  in  Plants. — Peroxid   Method. — Provisional. — Place 
from  1.5  to  2.5  grams  of  material  in  a  nickel  crucible  of  about 
100  cubic  centimeters  capacity  and  moisten  with  approximately 
two  cubic  centimeters  of  water.     Mix  thoroughly,  using  a  nickel 
or  platinum  rod.     Add  five  grams  of  pure  anhydrous  sodium 
carbonate  and  mix.     Add  pure  sodium  peroxid,  small  amounts 
(approximately  0.50  gram)    at  a  time,  thoroughly  mixing  the 
charge,  after  each  addition.     Continue  adding  the  peroxid  un- 
til the  mixture  becomes  nearly  dry  and  quite  granular,  requir- 
ing usually   about  five  grams  of  peroxid.     Place   the   crucible 
over  a  low  alcohol  flame  (or  other  flame  free  from  sulfur)  and 
carefully  heat  with  occasional  stirring  until  contents  are  fused. 
Should  the  material  ignite,  the  determination  is  worthless.  After 
fusion  remove  the  crucible,  allow  to  cool  somewhat,  and  cover 


STATING    RESULTS    OF    FERTILIZER    ANALYSIS  621 

the  hardened  mass  with  peroxid  to  a  depth  of  about  0.5  centi- 
meters. Heat  gradually,  and  finally  with  full  flame  until  com- 
plete fusion  takes  place,  rotating  the  crucible  from  time  to  time 
in  order  to  bring  any  particles  adhering  to  the  sides  into  contact 
with  the  oxidizing  material.  Allow  to  remain  over  the  lamp 
for  ten  minutes  after  fusion  is  complete.  Cool  somewhat,  place 
warm  crucible  and  contents  in  a  600  cubic  centimeter  beaker  and 
carefully  add  about  100  cubic  centimeters  of  the  water.  After 
violent  action  has  ceased,  wash  the  material  out  of  the  crucible, 
make  slightly  acid  with  hydrochloric  acid  (adding  small  portions 
at  a  time),  transfer  to  a  500  cubic  centimeter  flask,  cool,  and 
make  to  volume.  Filter  and  use  a  200  cubic  centimeter  aliquot 
for  determination  of  sulfates  by  precipitating  with  barium  chlo- 
rid  in  the  usual  manner. 

9.  Chlorin  in  Plants  (Provisional). — Saturate  five  grams  of 
the  sample  in  a  platinum  dish  with  20  cubic  centimeters  of  a  five 
per  cent,  solution  of  sodium  carbonate,  evaporate  to  dryness,  and 
ignite  as  thoroughly  as  possible'  Extract  the  residue  with  hot 
water,  filter  and  wash.  Return  it  to  the  platinum  dish,  ignite  to 
an  ash,  dissolve  in  nitric  acid,  and  determine  the  chlorin  by  the 
usual  method. 

523.  Stating  Results  of  Fertilizer  Analysis. — There  is  much 
difference  of  opinion  respecting  the  manner  in  which  the  results 
of  fertilizer  analyses  should  be  expressed.  The  matter  may  be 
looked  at  from  two  points  of  view,  first,  the  strictly  scientific 
expression  for  the  use  of  scientific  men  alone,  and,  second,  well 
known  terms  for  the  use  of  farmers.  Inasmuch  as  the  object 
of  the  inspection  of  fertilizers,  that  is,  fertilizer  control,  is  to 
acquaint  the  farmers  with  the  character  of  the  goods  they  pur- 
chase, it  is  evident  that  the  method  of  expressing  the  results 
of  analyses  when  exercised  for  the  control  and  sale  of  fertilizers 
should  be  in  terms  easily  understood  by  the  farmer.  In  the 
United  States  it  has  been  a  very  common  method  of  expression 
to  use  the  terms  "potash,"  "phosphoric  acid"  and  "ammonia" 
in  designating  the  three  important  constituents  of  fertilizers. 
The  farmers  of  this  country,  as  a  rule,  are  well  acquainted  with 
the  meaning  of  these  terms.  By  potash  the  potassium  oxid 


622  AGRICULTURAL  ANALYSIS 

(K2O),  by  phosphoric  acid  phosphoric  anhydrid  (P2O5),  and 
by  ammonia  the  total  nitrogen  expressed  as  ammonia,  namely, 
H3N,  are  meant.  This  latter  constituent  is  also  very  frequently 
expressed  "nitrogen  as  ammonia."  In  some  parts  of  the  coun- 
try it  is  customary  to  calculate  the  phosphoric  acid  as  trical- 
cium  phosphate.  In  this  form  the  name  which  is  very  com- 
monly employed  is  "bone  phosphate"  or  "bone  phosphate  of 
lime"  whether  it  be  made  from  bone  directly  or  from  phosphate 
rocks. 

In  some  of  the  States  the  origin  of  the  nitrogen  is  also  re- 
quired to  be  placed  upon  the  label  and  also  its  character,  namely, 
nitrogen  as  nitrates,  nitrogen  as  organic  matter,  etc.,  or,  if  cer- 
tain forms  of  organic  matter  be  used,  namely,  leather  or  hair, 
this  fact  is  also  required  to  be  stated.  There  is  also  a  very 
strong  movement  in  the  United  States  to  secure  the  expression 
of  results  of  analyses  of  fertilizers  in  the  elemental  form,  name- 
ly, nitrogen  (N),  phosphorous  (P),  potassium  (K),  calcium 
(Ca),  magnesium  (Mg),  iron  (Fe),  etc.  There  is  also  some 
influence  brought  to  bear  in  the  United  States  to  report  the  re- 
sults of  the  analysis  of  fertilizers  in  their  ionic  form. 

The  whole  matter  of  the  uniform  notation  of  the  results  of 
the  analyses  of  fertilizers  in  the  United  States  is  complicated  by 
the  large  number  of  State  laws  requiring  a  certain  form  of  ex- 
pression. Even  if  the  agricultural  chemists  of  the  country 
should  agree  upon  a  common  form  it  would  require  legislation 
in  many  States  to  make  it  effective. 

524.  Objections  to  the  Elemental  System. — The  objections  to 
*he  elemental  system  of  nomenclature  may  be  summarized  as 
follows  as  applying  to  the  United  States.91 

i.  The  proposed  elemental  system  is  used  only  by  one  State; 
the  common  form,  namely,  K2O  potash,  P2O5  phosphoric  acid, 
and  N  nitrogen  or  H3N  ammonia,  is  used  by  nearly  all  the  other 
States  and  by  many  foreign  countries.  The  adoption  of  the 
elemental  system  will  produce  confusion  among  the  States,  and 
even  if  adopted  by  all  the  States  would  not  be  in  harmony  with 
the  practice  of  other  countries. 

31  Fraps,  Preliminary   Report  on  the   Unification    of   Terms,  Bureau  of 
Chemistry,  Unnumbered  Circular,  1905  :  4. 


ADVANTAGES    OF    THE    ELEMENTAL    SYSTEM  623 

2.  The   common   system   of  notation   mentioned   above   is   in- 
corporated in  the  fertilizer  laws  of  27  of  the  States.     Any  change 
would    require    legislative    action    to    ratify    it    in    all    of   these 
States. 

3.  A    change    in    the    terms   which  are  commonly   used  will 
cause  confusion  in  the  minds  of  a  multitude  of  farmers,  manu- 
facturers and  dealers  who  are  acquainted  with  the  terms  now 
in  use. 

4.  The  apparent  decrease  of  20  per  cent,  in  the  amount  of 
potash  and  50  per  cent,  in  the  amount  of  phosphoric  acid  which 
would  result  from  the  adoption  of  the  new   system  would  re- 
quire a  great  deal  of  explanation  to  make  it  clear  to  the  farm- 
ers. 

5.  The  use  of  the  double  system  of  notation  for  fertilizers  in 
order  to   introduce  the  new   system   is   undesirable   and   would 
result  in  confusion. 

525.  Advantages  of  the  Elemental  System. — Hopkins  recom- 
mends reporting  all  analyses,  as  far  as  possible,  on  the  uniform 
basis  of  chemical  elements  as  follows  :92 

For  fertilizers  :  For  soils  : 

Nitrogen  (N).  Sulfur  (S). 

Phosphorus  (P).  Inorganic  carbon  (C). 

Potassium  (K).  Organic  carbon  (C). 

For  soils  :  Aluminum  (Al). 

Nitrogen  (N).  Manganese  (Mn). 

Phosphorus  (P).  Sodium  (Na). 

Potassium  (K).  Chlorin  (Cl). 

Calcium  (Ca).  Silicon  (Si). 

Magnesium  (Mg).  Insoluble  matter. 

Iron  (Fe).  Hydrogen  and  oxygen. 

The  hydrogen  and  oxygen  may  be  reported  "by  difference," 
or,  if  desired,  they  can  be  computed  in  the  usual  manner  by  cal- 
culating the  oxygen  necessary  to  form  oxids  with  certain  of  the 
determined  elements  and  adding  to  this  the  loss  in  ignition  (af- 
ter deducting  the  amount  of  volatile  elements  determined).  Sili- 
con (Si)  can  be  reported  if  determined  separately  from  the  in- 
soluble matter.  Of  course,  in  ultimate  analyses,  by  the  fusion 

"2  Bureau  of  Chemistry,  Preliminary  Report  on  the  Unification  of  Terms, 
Unnumbered  Circular,  1905  :  2. 


624  AGRICULTURAL  ANALYSIS 

method,  the  insoluble  matter  disappears.  It  will  be  seen  that 
there  is  no  difficulty  whatever  in  reporting  soil  analyses  by  this 
method.  This  has  already  been  demonstrated  and  illustrated  by 
the  Ohio  experiment  station.93 

In  considering  the  different  forms  of  nitrogen  we  can  report 
nitrate  nitrogen,  ammonia  nitrogen,  and  organic  nitrogen;  and, 
if  necessary,  we  can  also  distinguish  between  organic  and  inor- 
ganic sulfur  and  between  organic  and  inorganic  phosphorus, 
as  we  do  between  organic  and  inorganic  carbon.  A  complete 
analysis  of  potassium  chlorid  would  be  reported: 

Per  cent. 

Potassium 52 

Chlorin 48 

Total loo 

Whereas  under  the  qjd  system  we  have: 

Per  cent. 

Potash  (K2O) 63 

Chlorin  (Cl) 48 

Total 113 

Less  oxygen  replaced  by  chlorin 13 

TOO 

One  of  the  reasons  for  adopting  thi?  system  is  to  secure  ul- 
timate uniformity.  At  the  present  time  there  is  no  uniformity. 

Nitrogen. — A  majority  of  the  States  already  report  nitrogen 
as  N,  but  several  States  report  it  as  NH3,  and  the  Bureau  of 
Soils  reports  it  as  NO3,  NH8,  and  N. 

Phosphorus. — The  Bureau  of  Soils  reports  phosphorus  as  PO4, 
P2O5,  or  P.  Illinois  reports  it  as  P,  and  all  other  States  as 
P205. 

Potassium. — The  Bureau  of  Soils  and  the  State  of  Illinois  re- 
port potassium  as  K,  and  all  other  States,  also  the  Bureau  of 
Soils,  report  it  as  K2O. 

The  various  State  laws  with  few  exceptions  permit  the  use 
of  "equivalents"  in  addition  to  the  required  statement  of  analy- 
sis. Thus  a  uniform  statement  giving  both  N  and  NH3,  P  and 
P2O0,  K  and  K2O  could  be  used  by  all  manufacturers,  and  it 
K  Ohio  Agricultural  Experiment  Station,  Bulletin  150,  1904  :  131. 


KINDS  OF  INSECT  PESTS  625 

would  be  acceptable  in  almost  every  State  under  the  present 
laws.  If  this  double  statement  were  prepared  in  the  simplest 
form  it  would  not  be  objectionable,  and  it  would  not  require  any 
immediate  or  special  legislation,  excepting  in  one  or  two  States. 
The  following  form  is  suggested: 

Per  cent.  Per  cent. 

Nitrogen 1.4  =  Ammonia 1.7 

Available  phosphorus 6.4  =  Available  phosphoric  acid 14.4 

Insoluble  phosphorus 0.6  =  Insoluble  phosphoric  acid  •  •  •  •     1.4 

Total  phosphorus 7.0  —  Total  phosphoric  acid 15.8 

Potassium 3.9  =  Potash 4.7 

526.  Ingredients  Expressed  as  Ions. — The  expressions  of  the 
results  of  fertilizer  analyses  in  the  ionic  nomenclature  is  prac- 
ticed by  the  Bureau  of  Soils.     One  of  the  advantages  of  this 
system  is  to  secure  an  expression  of  analytical  data  in  a  man- 
ner conformable  to  the  piesent  leading  theory  of  the  constitu- 
tion of  matter.     This  method  of  expression  is  open  to  the  same 
criticism  as  that  applied  to  the  elemental  system.     It  has  the 
merit  however,  not  possessed  by  the  elemental  system,  of  being 
more  in  accord  with  modern  theories. 

527.  General  Conclusion. — It  appears  therefore  as  the  general 
consensus  of  opinion  in  the  United  States  that  the  present  sys- 
tem for  the  expression  of  the  results  of  fertilizer  analyses  and 
also  of  the  same  elements  as  determined  in  the  soil  should  be  as 
follows :     Nitrogen  N ;     phosphoric  acid  P2O5 ;     potash  K,O ; 
silica  SiO2;  soda  Na2O;  lime  CaO;  magnesia  MgO;  ferric  oxid 
Fe2O3 ;  alumina  A12O3 ;  sulfur  trioxid  SO3 ;  carbon  dioxid  CO2. 
This  would  not  preclude  the  additional  statement  of  the  data  in 
cither  elemental  or  ionic  form  as  described. 

METHODS  OF  ANALYSIS  OF  INSECTICIDES  AND 
FUNGICIDES 

528.  Kinds   of  Insect  Pests. — Various   groups  of  insects   act 
harmfully  on  plants,  or  animals,  or  as  pests  in  households,  or 
granaries ;  and  require  special  methods  of  treatment  to  kill  them.94 
Among  these  classes  of  insects  may  be  mentioned  internal  feed- 
ers, subterranean  insects,  insects  affecting  stored  products,  house- 

94  Haywood,  Manuscript  Communication  to  the  Author,  1908. 


626  AGRICULTURAL,  ANALYSIS 

hold  pests,  and  animal  parasites.  The  insects  which  principally 
injure  plants  however,  and  for  which  insecticides  are  most  often 
applied  are  external  feeders,  which  include  "biting"  and  "suck- 
ing" insects.95 

Biting  insects  are  those  which  actually  eat  some  part  of  the 
solid  substance  of  the  plant  as  the  leaf,  bark,  flower,  etc.  For 
these  some  poisonous  substance  is  used,  which  can  be  sprayed 
on  the  parts  of  the  tree  attacked  and  then  be  eaten  by  the  in- 
sect in  its  food. 

Sucking  insects,  are  those  which  live  by  sucking  the  plant 
juices  from  leaf,  bark,  fruit,  etc.  For  these  insecticides  must 
be  used  which  kill  the  insect  either  by  their  causticity,  by  smoth- 
ering, through  closing  the  breathing  pores,  or  by  filling  the  air 
around  the  insect  with  poisonous  fumes. 

Classification  of  Insecticides. — From  the  above  it  will  be  seen 
that  insecticides  may  be  classified  according  to  the  group  of 
insects  upon  which  they  act,  in  the  following  manner: 

Insecticides  used  against 

1.  External  feeders: 

(a)  Biting  insects. 

(b)  Sucking  insects. 

2.  Internal  feeders. 

3.  Subterranean   insects. 

4.  Insects    affecting   stored    products. 

5.  Household  pests. 

6.  Animal  parasites. 

Since  the  methods  used  in  combating,  as  well  as  the  insecticides 
used  against,  internal  feeders  and  household  pests  are  extremely 
varied,  it  does  not  seem  best  to  consider  these  classes  of  insecti- 
cides in  this  section. 

Following  are  descriptions  of  the  composition,  adulteration 
and  methods  of  analysis  of  the  principal  commercial  insecticides 
under  the  various  groups  enumerated  above,  such  as  the  chemist 
is  usually  called  upon  to  examine.  Those  insecticides  which 
are  home-made  and  do  not  require  analysis  by  the  chemist  are 
not  included. 

95  Marlatt,  Department  of  Agriculture,  Farmers'  Bulletin  127,  1901  :  7. 


PARIS   GREEN  627 

Insecticides  for  External  Biting  Insects. — This  group  of  in- 
secticides includes  paris  green,  green  arsenoid,  arsenate  of  lead, 
london  purple,  etc. 

529.  Paris  'Green. — Paris  green  is  supposed  to  be  copper-aceto 
arsenite  and  to  contain  31.29  per  cent,  copper  oxid,  58.65  per 
cent,  total  arsenious  oxid  and  10.06  per  cent,  acetic  acid.  On 
account  of  its  method  of  manufacture  it  may  contain  small 
amounts  of  dust  (determined  as  sand),  small  amounts  of  sodium 
sulfate,  and  larger  or  smaller  amounts  of  free  arsenious  oxid.  The 
following  constituents  therefore  are  usually  determined  in  the 
complete  analysis  of  a  sample  of  paris  green :  Moisture,  sand,  sul- 
furic  acid  calculated  as  sodium  sulfate,  total  arsenious  oxid, 
total  copper  oxid,  soluble  arsenious  oxid  and  acetic  acid  by  dif- 
ference. 

Analyses  of  Paris  Green. — Moisture. — Dry  one  to  two  grams 
for  eight  to  10  hours  at  105°  to  110°,  and  calculate  the  loss  as 
moisture.96 

Total  Arsenious  Oxid.  Method  7.97 — Solutions  Required. — (a). 
.Starch  Solution. — Use  a  starch  solution  which  is  prepared  by 
boiling  two  grams  of  starch  with  200  cubic  centimeters  of  dis- 
tilled water  for  about  five  minutes. 

(b)  Standard  Iodin  Solution. — Prepare  a  standard  iodin  solu- 
tion in  the  following  manner: — Dissolve  12.7  grams  of  pow- 
dered iodin  in  about  250  cubic  centimeters  of  water  to  which 
has  been  added  about  25  grams  of  chemically  pure  potassium 
iodid,  and  make  up  the  whole  to  a  volume  of  two  liters.  To 
standardize  this  solution,  weigh  one  gram  of  chemically  pure 
dry  arsenious  oxid,  transfer  to  a  250  cubic  centimeter  flask  by 
means  of  about  100  cubic  centimeters  of  a  solution  containing 
two  grams  of  sodium  hydroxid  in  each  100  cubic  centimeters, 
and  boil  until  all  arsenious  oxid  goes  into  solution.  Make  up 
to  a  volume  of  250  cubic  centimeters  and  use  50  cubic  centi- 
meters for  analysis.  Concentrate  this  portion  of  50  cubic  cen- 

96  Bureau  of  Chemistry,  Bulletin  107,  1907  :  25. 

97  Smith,  Journal  of  American  Chemical  Society,  1899,  21  :  769. 

Hay  wood,  Journal  of  the  American  Chemical  Society,    1900,  22  :  568. 
70S- 


628  AGRICULTURAL  ANALYSIS 

timeters  by  boiling  in  a  250  cubic  centimeter  flask  to  half  its 
volume,  and  allow  to  cool  to  about  80°.  Add  an  equal  volume 
of  concentrated  hydrochloric  acid  and  three  grams  of  potassium 
iodid,  mix,  and  allow  the  whole  to  stand  for  10  minutes  to  re- 
duce the  arsenic  oxid  formed  by  boiling  the  alkaline  arsenite 
to  arsenious  oxid.  Dilute  the  solution  with  cold  water  and  add 
an  approximately  tenth-normal  solution  of  sodium  thiosulfate, 
drop  by  drop,  until  the  solution  becomes  exactly  colorless.  This 
end  point  is  easy  to  read  without  the  aid  of  starch.  Make  this 
solution  slightly  alkaline  with  dry  sodium  carbonate,  using  a 
drop  of  methyl  orange  to  read  the  change,  and  then  make  slight- 
ly acid  with  hydrochloric  acid,  taking  care  that  all  lumps  of 
sodium  carbonate  on  the  bottom  are  acted  on  by  the  hydrochloric 
acid.  Add  sodium  bicarbonate  in  excess  and  run  in  the  solu- 
tion of  iodin  drop  by  drop,  using  starch  water  to  read  the  end 
reaction.  Sometimes  the  solution  becomes  dark  toward  the  end 
of  the  titration.  This  change  must  not  be  confused  with  the 
final  dark-blue  color  given  by  the  iodin-starch. 

From  the  number  of  cubic  centimeters  of  iodin  solution  and 
the  weight  of  arsenious  oxid  used  determine  the  value  of  each 
cubic  centimeter  of  iodin  in  terms  of  arsenious  oxid. 

Determination. — Transfer  two  grams  of  paris  green  to  a  250 
cubic  centimeter  flask  by  means  of  about  100  cubic  centimeters 
of  a  two  per  cent,  sodium-hydroxid  solution.  Boil  this  mixture 
for  five  to  10  minutes,  or  until  all  the  green  particles  have 
changed  to  red  cuprous  oxid,  then  cool  it  to  room  temperature 
and  make  the  volume  up  to  250  cubic  centimeters.  Filter  the 
well-shaken  liquid  through  a  dry  filter  and  use  50  cubic  centi- 
meter portions  for  analysis.  Conduct  the  analysis  from  this 
point  as  when  standardizing  the  iodin.  solution. 

Total  Arsenious  Oxid.  Method  7/.98 — Solutions  Required. —  (a) 
Standard  iodin  solution. — Prepare  an  iodin  solution  as  in  Method 
I.  To  standardize  this  solution  place  one  gram  of  dry,  chemical- 
ly pure  arsenious  oxid  in  a  250  cubic  centimeter  flask,  and  dis- 
solve by  boiling  about  20  minutes  with  five  grams  of  sodium  bi- 

98  Hay  wood,  Bureau  of  Chemistry,  Bulletin  81,  1904  :  195. 
Journal  of  the  American  Chemical  Society,  1903,  25  :  963. 
Bureau  of  Chemistry,  Bulletin  107,  1907  :  26. 


PARIS   GREEN  629 

carbonate  and  approximately  100  cubic  centimeters  of  water; 
cool,  add  hydrochloric  acid  until  acid,  and  then  sodium  bicar- 
bonate until  alkaline;  make  up  to  the  mark  and  titrate  aliquots 
of  50  cubic  centimeters  with  iodin  solution  as  in  Method  I. 

(b)  Sodium   acetate   solution. — Dissolve    12.5   grams   of   the 
crystallized  salt  in  each  25  cubic  centimeters. 

(c)  Sodium  potassium  tartrate  solution. — Dissolve  from  two 
to  three  grams  of  sodium  potassium  tartrate  in  each  50  cubic 
centimeters. 

(d)  Slarch  solution. — Prepare  a  starch  solution  as  in  Method  I. 
Determination. — Place  one  gram  of  paris  green  in  a  100  cubic 

centimeter  flask  and  boil  for  five  minutes  with  25  cubic  centi- 
meters of  the  sodium  acetate  solution.  Make  to  the  mark,  shake, 
and  pass  through  a  dry  asbestos  gooch  filter.  Use  an  aliquot 
of  this  filtrate  for  the  determination  of  the  soluble  arsenious  oxid 
by  means  of  the  iodin  solution.  Transfer  the  residue  on  the 
filter  to  a  beaker,  beat  up  with  a  little  water,  dissolve  in  con- 
centrated hydrochloric  acid  adding  a  drop  at  a  time,  then  add 
three  or  four  drops  in  excess.  Transfer  the  whole  to  the  100 
cubic  centimeter  flask  originally  employed  and  analyze  aliquots 
of  from  20  to  40  cubic  centimeters.  Add  concentrated  sodium 
carbonate  solution,  a  drop  at  a  time,  to  each  of  these  aliquots  un- 
til a  slight  permanent  precipitate  is  formed.  Dissolve  this  pre- 
cipitate by  adding  50  cubic  centimeters  of  the  sodium  potassium 
tartrate.  Dilute  to  about  200  cubic  centimeters,  add  solid  sodium 
bicarbonate  and  starch  water,  and  titrate  with  standard  iodin. 

Total  Arsenious  Oxid.    Method  III." — Solutions  Required. — 
Prepare  the  same  solutions   as   were  required   for  Method  II. 

Determination. — Boil   0.4   gram   of   the    finely   ground   paris 
green  with  25  cubic  centimeters  of  the  sodium  acetate  solution 
for   from  five  to    10  minutes.     Add  concentrated   hydrochloric 
acid,  a  drop  at  a  time,  until  solution  is  effected  (about  10  cubic 
centimeters   of   the    acid   is   usually   necessary).     Add   concen- 
trated sodium  carbonate  solution,  a  drop  at  a  time,  until  a  slight 
99  Haywood,  Bureau  of  Chemistry,   Bulletin  81,    1904  :  197. 
Journal  of  the  American  Chemical  Society,  1903,  25  :  963. 
Bureau  of  Chemistry,  Bulletin  107,  1907  :  26. 


630  AGRICULTURAL  ANALYSIS 

precipitate  appears,  then  proceed  as  directed  in  the  last  two  sen- 
tences of  Method  II. 

Sodium-Acetate-Soluble  Arsenious  O.rid.1 — Solutions  Re- 
quired.— Prepare  the  same  solutions  as  are  used  in  Method  II 
for  total  arsenious  oxid,  with  the  exception  of  the  sodium  po- 
tassium tartrate  solution. 

Determination. — Proceed  as  described  in  the  first  three  sen- 
tences of  Method  II  for  total  arsenious  oxid,  except  that  a  paper 
filter  is  used,  instead  of  asbestos. 

Water-Soluble  Arsenious  Oxid.  Method  I.2 — Solutions  Re- 
quired.— Prepare  starch  and  standard  iodin  solutions  as  de- 
scribed under  Method  II  for  total  arsenious  oxid. 

Determination. — Treat  one  gram  of  paris  green  in  a  large 
flask  with  1,000  cubic  centimeters  of  water  previously  boiled  to 
«xpel  carbon  dioxid  and  then  cooled  to  room  temperature.  Stop- 
per the  flask  and  shake  eight  times  each  day  for  ten  days.  At 
the  end  of  this  time  filter  the  solution  through  a  dry  filter.  Treat 
200  cubic  centimeters  of  this  filtrate  with  sodium  bicarbonate 
and  titrate  with  the  iodin  solution. 

Water-Soluble  Arsenious  Oxid.  Method  II.3 — Solutions  Re- 
quired.— The  same  solutions  are  required  as  are  used  in  Method 
I  for  water-soluble  arsenious  oxid. 

Determination. — Digest  one  part  of  paris  green  in  1,000  parts 
•of  water  for  twenty-four  hours  with  occasional  shaking.  At  the 
end  of  this  time  filter  through  a  dry  filter,  treat  an  aliquot  with 
sodium  bicarbonate  and  titrate  with  iodin  solution. 

Water-Soluble  Arsenious  Oxid.  Method  III.* — Solutions  Re- 
quired.— The  same  solutions  are  required  as  are  used  in  Method 
I  for  water-soluble  arsenious  oxid. 

1  Avery  and  Beans,    Journal  of  the  American  Chemical  Society,   1901, 
23  :  in. 

Bureau  of  Chemistry,  Bulletin  107,  1907  :  27. 

2  Haywood,  Journal  of  the  American  Chemical  Society,    1900,   22  :  568, 
705  ;    1901,  23  :  in. 

Bureau  of  Chemistry,  Bulletin  67,  1902  :  98. 

s  Cathcart,  New  Jersey  Agricultural -Experiment  Station,  Bulletin  205, 
1905  :  9. 

*  Colby,  California  Agricultural  Experiment  Station,  Bulletin  151,  1903  : 
18. 


PARIS    GREEN  631 

Determination. — Place  half  a  gram  of  paris  green  in  a  250 
cubic  centimeter  erlenmeyer  flask,  add  100  cubic  centimeters  of 
distilled  water  and  agitate  by  shaking  every  few  minutes  through- 
out a  working  period  (eight  hours)  of  a  clay,  keeping  the  liquid 
at  only  25°  to  30°.  The  next  day  after  pouring  off  the  clear 
liquid,  add  a  fresh  100  cubic  centimeter  portion  of  water  and 
repeat  the  treatment  mentioned  above.  Repeat  the  same  treat- 
ment on  a  third  day,  in  all  24  hours.  Finally,  combine  the  three 
TOO  cubic  centimeter  leachings,  filter  through  a  double  filter  and 
determine  arsenious  oxid  by  means  of  standard  iodin  in  the 
filtrate. 

Total  Copper  Oxid.  Met-hod  I.5 — Pour  the  cuprous  oxid  (ob- 
tained in  Method  I,  for  total  arsenious  oxid  by  boiling  the  paris 
green  with  sodium  hydroxid)  on  the  filter  and  wash  well  with 
hot  water,  after  an  aliquot  of  the  filtrate  has  been  used  for  the 
determination  of  arsenious  oxid.  Then  dissolve  in  hot  dilute 
nitric  acid  and  make  up  to  a  volume  of  250  cubic  centimeters. 
Use  50  to  ioo  cubic  centimeters  of  this  solution  for  the  electro- 
lytic determination  of  copper,  as  described  on  page  52,  para- 
graph (2),  under  "VII  General  Methods  for  the  Analysis  of 
Foods  and  Feeding  Stuffs."  Bulletin  107,  Bureau  of  Chemistry. 

Total  Copper  Oxid.  Method  7/.° — Solutions  Required. — Stand- 
ard thiosulfatc  solution.  Dissolve  24.8  grams  of  the  crystallized 
salt  and  make  up  to  two  liters.  Standardize  this  solution  against 
chemically  pure  copper  foil  dissolved  in  nitric  acid  by  the  method 
of  analysis  given  in  the  following  paragraph. 

Determination. — Use  an  aliquot  portion  of  the  nitric-acid  so- 
lution of  copper  oxid,  employed  in  Method  I  for  total  copper 
oxid.  Make  it  alkaline  with  sodium  carbonate,  then  make  slight- 
ly acid  with  acetic  acid,  dilute  with  water,  and  add  about  three 
or  four  grams  of  solid  potassium  iodid.  When  the  potassium 
iodid  is  all  dissolved  by  shaking,  titrate  the  free  iodin  with  thio- 
sulfate,  using  starch  as  indicator  toward  the  end  of  the  reaction. 

Total  Copper   Oxid.     Method  III.' — Solutions   Required. — A 

5  Bureau  of  Chemistry,   Bulletin  73,  1903  :  158;    Bulletin  81,  1904  :  195  ; 
Bulletin  90,  1905  :  95. 

6  Journal  of  the  American  Chemical  Society,  1900,   22  :  568. 
'  Bureau  of  Chemistry,  Circular  10,  1905,  Revised. 


•632  AGRICULTURAL  ANALYSIS 

fifth-normal  solution  of  potassium  cyanid  which  is  prepared  by 
standardizing  against  a  known  weight  of  copper  dissolved  in 
nitric  acid,  the  method  being  the  same  as  that  described  in  the 
following  paragraph. 

Determination. — Neutralize  an  aliquot  portion  of  the  nitric  acid 
solution  used  in  Method  I  for  total  copper  oxid  with  sodium  car- 
bonate and  add  a  trifling  excess  of  the  carbonate ;  add  one  cubic 
centimeter  of  0.960  specific  gravity  ammonia  and  titrate  the  dark 
Hue  solution  to  the  disappearance  of  the  blue  color  with  stand- 
ard potassium  cyanid. 

Sand. — Dissolve  the  sample  used  for  moisture  determination  in 
hydrochloric  acid,  filter,  wash,  dry  and  finally  burn  the  filter 
.and  calculating  the  residue  as  sand.8 

Sodium  Sulfate, — Treat  the  boiling  filtrate  from  the  deter- 
mination of  sand  with  a  boiling  solution  of  barium  chlorid,  al- 
low to  stand  until  the  precipitate  settles,  leaving  a  clear  solu- 
tion ;  filter,  wash,  dry  and  burn  with  the  usual  precaution  used 
in  determining  barium  sulfate.  Calculate  the  barium  sulfate 
found  to  sodium  sulfate,  since  it  is  in  this  form  that  sulfuric  acid 
is  supposed  to  be  present. 

Acetic  Acid. — This  figure  is  obtained  by  subtracting  the  sum  of 
the  other  constituents  from  100. 

530.  Discussion  of  Methods  of  Analysis  of  Paris  Green. — Hay- 
wood  has  very  carefully  tested  all  three  of  the  methods  given 
above  for  total  arsenious  oxid  and  has  found  that  all  of  them 
give  excellent  results.  The  methods  have  also  been  tested  by  the 
Association  of  Official  Agricultural  Chemists  with  like  results. 

The  electrolytic  method  for  total  copper  is  of  course  a  stand- 
ard method,  the  accuracy  of  which  has  long  since  been  deter- 
mined. The  thiosulfate  method  for  total  copper  gives  most  ex- 
cellent results  when  precautions  are  taken,  but  is  a  failure  unless 
certain  precautionary  details  are  followed  to  the  letter.  It  is  ab- 
solutely necessary  that  there  be  only  a  very  slight  excess  of  ace- 
tic acid  present  when  the  potassium  iodid  is  added,  otherwise 
iodine  is  continuously  set  free  and  an  end  point  can  not  be  ob- 
tained. It  is  also  necessary  that  the  chemist  be  very  careful 
8  Bureau  of  Chemistry,  Bulletin  68,  1902  :  13. 


LONDON  PURPLE  633. 

about  reading  the  end  point  when  the  standard  thiosulfate  solu- 
tion is  added  to  use  up  the  iodin  set  free.  The  end  point  is 
not  reached  when  the  solution  is  a  dirty  white,  but  only  when  the 
white  is  entirely  unsoiled  by  any  darker  coloring.  The  potas- 
sium cyanid  method  gives  very  fair  results  when  carefully  car- 
ried out,  but  there  is  a  tendency  to  get  figures  slightly  above  the 
truth. 

A  full  discussion  of  the  method  of  determining  sodium-acetate- 
soluble  arsenious  oxid  and  Method  I  of  determining  water-soluble 
arsenious  oxid  will  be  found  in  the  Proceedings  of  the  i8th  An- 
nual Convention  of  the  Association  of  Official  Agricultural  Chem- 
ists.9 To  what  is  said  there  of  water-soluble  arsenious  oxid, 
it  is  only  necessary  to  add  that  future  work  will  probably  show 
that  the  time  of  extraction  with  water,  i.  e.,  ten  days,  can  prob- 
ably be  considerably  reduced,  say  to  about  five  days,  without  in 
any  way  decreasing  the  value  of  the  method.  From  the  work 
performed  by  Colby  it  would  appear  that  Method  II  gives  re- 
sults considerably  below  the  truth,  in  that  all  free  arsenious  oxid 
is  not  dissolved  in  24  hours.10  Haywood  has  never  tested  Meth- 
od III  for  soluble  arsenious  oxid,  nor  has  he  seen  it  used  by 
any  one  but  Colby,  its  originator.  It  would  appear  that  this  last 
method  would  give  just  about  the  same  results  as  would  be  ob- 
tained by  extracting  one  part  of  paris  green  with  1000  parts  of 
water  for  three  to  five  days.  If  such  is  the  case,  it  would  be 
simpler  to  extract  all  at  once  instead  of  by  three  operations. 

531.  Green  Arsenoid. — The  same  methods  of  analysis  are  used 
in  examining  this  compound  as  are  used  for  paris  green,  except 
that   the   sum  of   moisture,   sand,    sodium   sulfate,   total   arsen- 
ious oxid  and  total  copper  subtracted  from  100  represents  col- 
oring matter  instead  of  acetic  acid. 

532.  London  Purple. — London  purple  is  a  by-product  obtained 
in  the  manufacture  of  certain  of  the  anilin  dyes.     It  is  com- 
posed principally  of  calcium  arsenate  and  calcium  arsenite  to- 
gether with  an  organic  dye  residue.     Both  the  calcium  arsenate 
and  arsenite  are  soluble  in  water  to  a  limited  extent,  but  in  ad- 
dition to  this  london  purple  may  contain  a  certain  amount  of 

9  Bureau  of  Chemistry,  Bulletin  67,  1902  :  98. 

10  California  Agricultural  Experiment  Station,  Bulletin  151,  1903  :  18. 


634  AGRICULTURAL  ANALYSIS 

"ic"  and  "ous"  arsenic  in  the  form  of  the  uncombined  oxids. 
Dirt  in  the  form  of  sand  may  also  be  present  in  the  mixture;  to 
a  limited  extent.  It  will  thus  be  seen  that  the  analysis  of  Ion- 
don  purple  should  include  determinations  of  moisture,  total  ar- 
senic oxid,  total  arsenious  oxid,  soluble  arsenic  oxid,  soluble  ar- 
senious  oxid,  calcium  oxid,  sand  and  the  dye  by  difference. 

Following  are  the  methods  of  analysis  commonly  used  in  deter- 
mining the  above  constituents. 

Moisture. — Dry  from  one  to  two  grams  for  from  10  to  12 
hours  at  a  temperature  of  105°  to  no0.11 

Total  Arsenious  Oxid.  Method  I. — Solutions  Required. — Pre- 
pare starch  and  iodin  solutions  by  either  of  the  methods  given 
under  paris  green. 

Determination. — Dissolve  two  grams  of  london  purple  in  a 
mixture  of  about  80  cubic  centimeters  of  water  and  20  cubic  cen- 
timeters of  concentrated  hydrochloric  acid  at  a  temperature  of 
from  60°  to  70°  ;  filter  and  wash  to  a  volume  of  300  cubic  cen- 
timeters. Treat  100  cubic  centimeters  of  this  solution  with  so- 
dium bicarbonate  in  excess  and  make  up  to  the  mark  in  a  500 
cubic  centimeter  flask,  using  a  few  drops  of  ether  to  destroy  the 
bubbles.  Pass  a  portion  through  a  dry  filter,  and  to  250  cubic 
centimeters,  add  starch  water,  and  titrate  the  solution  with  stand- 
ard iodin  to  the  appearance  of  a  blue  color.  The  result  is  the 
arsenious  oxid,  as  such,  in  50  cubic  centimeters  of  the  original 
solution,  or  in  0.3333  gram  of  the  original  london  purple. 

Total  Arsenious  Oxid.  Method  7/.12 — The  method  is  designed 
to   eliminate   part   of   the    coloring   matter.     The    solutions    re 
quired  are  as  in  Method  I  for  total  arsenious  oxid. 

Determination. — Place  two  grams  of  london  purple  in  a  beak- 
er and  dissolve  in  about  80  cubic  centimeters  of  water  and  20 
cubic  centimeters  of  concentrated  hydrochloric  acid  at  a  tem- 
perature of  60°  to  70°,  cool  and  add  sodium  carbonate  in  slight 
excess,  transfer  to  a  250  cubic  centimeter  flask,  bring  to  the 
mark,  shake,  and  filter  through  a  dry  filter.  Acidifv  50  cubic 
centimeters  of  the  filtrate  with  hydrochloric  acid  and  make  al- 

11  Haywood,  Journal  of  the  American  Chemical  Society,  1900,  22  :  800. 
Bureau  of  Chemistry,  Bulletin  107,  1907  :  28. 

12  Bureau  of  Chemistry,  Bulletin  81,  1904  :  199;  Bulletin  107,  1907  :  29. 


LONDON  PURPLE;  635 

kaline  with  sodium  bicarbonate.  Titrate  the  amount  of  arsen- 
ious  oxid  present  with  the  standard  iodin  solution. 

Total  Arsenic  Oxid.  Method  7.13 — Solutions  Required. — Use 
the  same  solutions  as  described  above  for  total  arsenious  oxid. 

Determination. — Heat  50  cubic  centimeters  of  the  hydrochloric 
acid  solution  of  london  purple  prepared  by  the  preceding  meth- 
od, to  80°  on  the  water  bath,  remove  and  add  50  cubic  centi- 
meters of  concentrated  hydrochloric  acid  and  three  grams  of  po- 
tassium iodid.  Allow  the  mixture  to  stand  for  at  least  15  min- 
utes, the  arsenic  acid  thus  being  reduced  to  the  arsenious  con- 
dition and  the  iodin,  set  free. 

Then  rinse  the  solution  into  a  large  beaker,  dilute  well,  and  add 
twentieth-normal  sodium  thiosulfate,  drop  by  drop,  to  eliminate 
the  free  iodin.  The  end  point  here  is  rather  difficult  to  read  en 
account  of  the  very  dark  color  of  the  solution,  but  with  a  little 
practice  the  chemist  can  determine  it  by  proceeding  as  follows : 

Run  in  the  sodium  thiosulfate  a  little  at  a  time,  occasionally 
withdrawing  a  drop  of  the  solution  and  adding  it  to  a  drop  of 
starch  paste.  This  will  give  a  blue  color  of  varying  intensity, 
which  becomes  fainter  as  the  iodin  is  used  up.  Finally 
when  a  drop  of  the  solution  gives  only  the  slightest  blue  color 
with  the  starch,  add  a  little  starch  paste  directly  to  the  whole 
solution  and  dissipate  the  blue  color  with  a  few  drops  of  thio- 
sulfate. With  a  little  practice  the  chemist  can  in  this  way  get 
the  exact  end  point.  Immediately  make  the  solution  alkaline 
with  solid  sodium  carbonate.  Again  make  it  slightly  acid  with 
hydrochloric  acid,  taking  care  that  all  of  the  solid  particles  of 
the  sodium  carbonate  on  the  bottom  are  neutralized  by  the  acid, 
and  finally  make  alkaline  with  sodium  bicarbonate.  Add  starch 
paste  and  titrate  with  the  standard  iodin  solution.  The  end 
point  is  easily  read  if  the  beaker  is  placed  on  a  white  surface 
between  the  eye  and  the  light  and  the  iodin  solution  run  in 
until  a  distinct  purple  color  appears.  The  figure  thus  obtained 
gives  the  number  of  cubic  centimeters  of  iodin  corresponding 
to  the  total  amount  of  arsenic  in  the  solution  expressed  as  ar- 
senious oxid.  Subtracting  from  this  the  number  of  cubic  cen- 
13  Haywood,  Journal. of  the  American  Chemical  Society,  1900,  22  :  800. 


636  AGRICULTURAL   ANALYSIS 

timeters  of  iodin  corresponding  to  the  arsenious  oxid  in  the  pre- 
vious method  gives  the  number  of  cubic  centimeters  of  iodin 
corresponding  to  the  arsenic  oxid  in  0.3333  gram  of  the  sample. 

Total  Arsenic  Oxid.  Method  II. — The  method  is  designed 
to  eliminate  part  of  coloring  matter.  The  solutions  required  are 
the  same  as  in  Method  I  for  total  artenious  oxid. 

Determination. — Acidify  50  cubic  centimeters  of  the  solution, 
prepared  as  directed  in  the  preceding  paragraph,  with  concen- 
trated hydrochloric  acid,  heat  to  80°,  add  50  cubic  centimeters 
more  of  hydrochloric  acid  and  three  grams  of  potassium  iodid, 
and  proceed  as  described  in  Method  I  for  total  arsenic  oxid  in 
london  purple  beginning  with  the  second  sentence. 

Water-Soluble  Arsenious  Oxid.™ — Use  the  same  solutions  as 
in  Method  I  for  total  arsenious  oxid. 

Determination. — Extract  one  gram  oi  london  purple  in  a  stop- 
pered flask  with  500  cubic  centimeters  of  cold  carbon  dioxid 
free  water  for  seven  days,  shaking  eight  times  each  day.  Filter 
through  a  dry  filter;  to  100  cubic  centimeters  of  filtrate,  add 
sodium  bicarbonate,  and  titrate  with  standard  iodin,  using  starch 
as  indicator. 

Water-Soluble  Arsenic  Oxid. — Use  the  same  solutions  as  in 
Method  I  for  total  arsenious  oxid. 

Determination. — Transfer  an  aliquot  (about  200  cubic  cen- 
timeters) of  the  water  extract  from  the  determination  of  soluble 
arsenious  oxid  to  a  flask,  make  slightly  alkaline  with  sodium 
hydroxid,  and  concentrate  to  about  25  cubic  centimeters.  Re- 
move the  flask  and  allow  it  to  cool  to  about  80°,  and  add  an 
equal  volume  of  concentrated  hydrochloric  acid  and  three  grams 
of  potassium  iodid.  Allow  it  to  stand  15  minutes,  dilute,  exactly 
use  up  the  iodin  set  free  with  twentieth-normal  thiosulfate  (us- 
ing starch  if  necessary),  and  neutralize  the  solution  with  sodium 
carbonate.  Again  make  slightly  acid  with  hydrochloric  acid, 
taking  care  that  all  lumps  of  sodium  carbonate  are  acted  on,  then 
make  alkaline  with  an  excess  of  sodium  bicarbonate,  and  titrate 
with  iodin,  using  starch  as  indicator.  From  this  figure  subtract 

14  Haywood,   Journal  of  the  American  Chemical  Society,  1900,  22  '  800. 
Bureau  of  Chemistry,  Bulletin  107,  1907  :  29.  . 


ANALYSIS    OF    LONDON     PURPLE  637 

the  figure  representing  the  amount  of  soluble  arsenious  oxid, 
and  calculate  the  remainder  as  arsenic  oxid. 

Calcium  Oxid. — Dissolve  a  portion  of  london  purple  in  hy- 
drochloric acid  by  the  aid  of  heat,  filter,  wash  the  residue  with 
hot  water,  and  pass  hydrogen  sulfid  through  the  filtrate.  Wash 
the  precipitate  so  obtained  in  the  filter  with  hot  water  till  clean. 
Evaporate  the  filtrate  to  a  small  bulk,  transfer  to  a  200  cubic  cen- 
timeter flask,  treat  with  ammonium  hydroxid  to  precipitate  iron 
and  make  to  the  mark.  Filter  the  solution  through  a  dry  paper 
and  determine  the  calcium  in  an  aliquot  portion  of  the  filtrate 
by  means  of  ammonium  oxalate. 

Sand.15 — Dry  the  residue  remaining  from  the  hydrochloric  acid 
extraction  in  the  previous  method,  transfer  to  a  crucible,  burn 
paper  and  contents,  and  finally  weigh  as  sand. 

533.  Discussion  of  Methods  of  Analysis  of  London  Purple. — 
Method  I  for  total  arsenious  and  arsenic  oxid  have  been  care- 
fully tested  by  Haywood  and  excellent  results  have  been  ob- 
tained. The  Association  of  Official  Agricultural  Chemists  has 
also  tested  Method  I,  sometimes  obtaining  good  results  and 
sometimes  obtaining  widely  divergent  results.  It  is  undoubted- 
ly true  that  it  is  extremely  difficult  to  read  the  two  end  points 
in  Method  I  for  total  arsenic  oxid,  i.  e.,  the  point  where  the 
thiosulfate  uses  up  all  the  iodin  and  the  point  where  all  arseni- 
ous oxid  is  oxidized  to  arsenic  oxid  by  standard  iodin,  however 
by  closely  following  the  directions  it  is  easy  to  obtain  closely 
agreeing  results. 

Method  II  for  total  arsenious  and  arsenic  oxid  have  also  been 
tested  by  Haywood  and  results  were  obtained  that  closely  agreed 
with  the  results  obtained  by  Method  I.  The  Association  of 
Official  Agricultural  Chemists  has  also  tested  Method  II,  but 
with  unsatisfactory  results  up  to  the  present  time,  the  tendency 
being  to  obtain  low  results  on  arsenious  oxid  and  high  results 
on  arsenic  oxid.  Method  II  is  a  decided  improvement  on  Meth- 
od I,  as  it  greatly  lessens  the  difficulty  of  reading  the  two  end 
points  mentioned  above  and  gives  equally  good  results. 

The  methods  for  determining  soluble  arsenious  and  arsenic 
15  Bureau  of  Chemistry,  Bulletin  68,  1902  :  20. 


638  AGRICULTURAL  ANALYSIS 

oxids  have  been  carefully  tested  by  the  Association  of  Official 
Agricultural  Chemists  and  have  usually  given  good  results. 

534.  Lead  Arsenate.10 — Lead  arsenate  is  usually  prepared  by  the 
action  of  either  lead  acetate,  or  lead  nitrate  on  crystallized  di- 
sodium  hydrogen  arsenate  and  usually  comes  on  the  market  in 
the  form  of  a  thick  paste.  In  making  an  analysis  of  this  com- 
pound, the  following  determinations  are  usually  made:  Mois- 
ture, total  arsenic  oxid,  soluble  arsenic  oxid,  total  lead  oxid,  sol- 
uble lead  oxid,  and  soluble  impurities  (exclusive  of  soluble  lead 
oxid  and  arsenic  oxid). 

General  Direction. — In  case  the  sample  is  in  the  form  of  a 
paste,  as  it  usually  is,  dry  the  whole  of  it  to  constant  weight  at 
the  temperature  of  boiling  water  and  calculate  the  results  as 
total  moisture.  Grind  the  dry  sample  (which  will  gain  a  small 
amount  of  moisture  by  so  doing)  to  a  fine  powder  and  deter- 
mine the  various  constituents  as  follows : 

Moisture. — Heat  two  grams  of  the  sample  in  the  water  bath 
for  eight  hours  or  in  the  hot  air  bath  at  110°  for  five  to  six 
hours  or  till  constant  weight  is  obtained. 

Total  lead  oxid. — Dissolve  two  grams  of  the  sample  in  about 
80  cubic  centimeters  of  water  and  15  cubic  centimeters  of  con- 
centrated nitric  acid  on  the  steam  bath :  transfer  the  solution  to 
a  250  cubic  centimeter  flask  and  make  up  to  the  mark.  To  50 
cubic  centimeters  of  the  solution  add  three  cubic  centimeters  of 
concentrated  sulfuric  acid,  evaporate  on  the  steam  bath  to  a  sirupy 
consistency  and  then  on  a  hot  plate  till  white  fumes  appear  and 
all  nitric  acid  has  been  given  off.  Add  50  cubic  centimeters  of 
water  and  100  cubic  centimeters  of  95  per  cent,  alcohol,  let  stand 
for  several  hours  and  filter  off  the  supernatant  liquid,  wash  about 
ten  times  with  acidified  alcohol  (water  100  parts,  95  per  cent,  al- 
cohol 200  parts,  and  concentrated  sulfuric  acid  three  parts)  and 
then  with  95  per  cent,  alcohol  till  free  of  sulfuric  acid.  Dry, 
remove  as  much  as  possible  of  the  precipitate  from  the  paper 
into  a  weighed  crucible,  and  ignite  at  a  low  red  heat.  Burn  the 
paper  in  a  separate  porcelain  crucible  and  treat  the  residue  first 
with  a  little  nitric  acid,  which  is  afterwards  evaporated  off,  and 

18  Haywood,  Bureau  of  Chemistry,  Bulletin  105,   1907  :  165. 


LEAD   ARSENATE  639 

then  with  a  drop  or  two  of  sulfuric  acid.  Ignite,  weigh,  and 
add  this  weight  to  the  weight  of  the  precipitate  previously  re- 
moved from  the  paper  for  amount  of  the  lead  sulfate. 

Water-soluble  lead  oxid. — Place  two  grams  of  lead  ar senate  in 
a  flask  with  2,000  cubic  centimeters  of  carbon  dioxid  free  water 
and  let  stand  ten  days,  shaking  eight  times  a  day.  Filter  through 
a  dry  filter  and  use  aliquots  of  this  for  determining  soluble  lead 
and  arsenic  oxids  and  soluble  solids ;  determine  lead  as  described 
above  for  total  lead  oxid,  using  the  same  relative  proportions  of 
sulfuric  acid,  water,  and  alcohol,  but  keeping  the  volume  as 
small  as  possible. 

Total  arsenic  oxid. — Transfer  100  cubic  centimeters  of  the 
nitric  acid  solution  of  the  sample,  prepared  as  in  the  above  de- 
termination of  lead,  to  a  porcelain  dish,  add  six  cubic  centime- 
ters of  concentrated  sulfuric  acid,  evaporate  to  a  sirupy  consis- 
tency on  the  water  bath  and  then  on  a  hot  plate  to  the  appear- 
ance of  white  fumes  of  sulfuric  acid.  Wash  into  a  100  cubic 
centimeter  flask  with  water,  make  up  to  mark,  filter  through  dry 
filters,  and  use  50  cubic  centimeter  aliquot  parts  for  further 
work.  Transfer  this  to  an  erlenmeyer  flask  of  400  cubic  centi- 
meters capacity,  add  four  cubic  centimeters  of  concentrated  sul- 
furic acid  and  one  gram  of  potassium  iodid,  dilute  to  about  100 
cubic  centimeters  and  boil  until  the  volume  is  reduced  to  about 
40  cubic  centimeters.  Cool  the  solution  under  running  water, 
dilute  to  about  300  cubic  centimeters,  and  exactly  use  up  the  io- 
din  set  free  and  still  remaining  in  solution  with  a  few  drops  of 
approximately  tenth-normal  sodium  thiosulfate  solution.  Wash 
the  mixture  into  a  large  beaker,  make  alkaline  with  sodium  car- 
bonate, and  slightly  acidify  with  dilute  sulfuric  acid ;  then  make 
alkaline  again  with  an  excess  of  sodium  bicarbonate.  Titrate  the 
solution  with  a  twentieth-normal  iodin  solution  to  the  appearance 
of  a  blue  color,  using  starch  as  indicator. 

Water-soluble  arsenic  oxid. — For  this  determination  use  200 
to  400  cubic  centimeters  of  the  water  extract  obtained  under  the 
determination  of  soluble  lead  oxid.  Add  0.5  cubic  centimeter 
of  sulfuric  acid  and  evaporate  it  to  a  sirupy  consistency,  then 
heat  on  a  hot  plate  to  appearance  of  white  fumes.  Add  a  very 


640  AGRICULTURAL  ANALYSIS 

small  amount  of  water  and  filter  the  lead  through  the  very  small- 
est filter  paper,  using  as  little  wash-water  as  possible.  Place 
this  filtrate  in  an  erlenmeyer  flask,  and  determine  arsenic  as 
described  above  for  total  arsenic  oxid,  using  the  same  amount  of 
reagents  and  the  same  dilutions. 

Soluble  solids  or  impurities. — Evaporate  200  cubic  centime- 
ters of  the  water  extract  obtained  above  to  dryness  in  a  weighed 
platinum  dish,  dry  to  constant  weight  at  the  temperature  of  the 
boiling  water  bath  and  weigh.  The  soluble  solids  so  obtained 
represent  principally  any  sodium  acetate  or  sodium  nitrate  pres- 
ent, with  a  very  small  quantity,  perhaps,  of  lead  acetate  or 
nitrate  and  some  soluble  arsenic,  probably  in  the  form  of  lead 
arsenate. 

The  above  methods  for  determining  the  constituents  of  com- 
mercial lead  arsenate  have  been  carefully  tested  by  Haywood, 
as  well  as  by  several  other  chemists  all  of  whom  have  reported 
that  exceptionally  good  results  were  obtained. 

535.  Insecticides  for  External  Sucking  Insects. — This  group  of 
insecticides  includes  soaps,  caustic  soda  and  potash,  lime-sulfur- 
salt  mixtures,  kerosene  emulsions,  dilute  nicotine  solutions,  hy- 
drocyanic acid  gas,  vapors  of  carbon  bisulfid,  etc. 

536.  Soaps. — Soap  may  be  used  to  destroy  soft  bodied  insects, 
such  as  plant  lice,  and  in  strong  solutions,  as  a  winter  wash  to 
destroy  scale  insects.     Fish  oil  soap,  prepared  by  the  action  of 
caustic  potash  or  soda  on  fish  oil  is  one  of  the  most  effective 
soaps,  and  is  the  one  which  the  chemist  is  most  often  called 
upon  to  examine.     The  potash  soap  is  the  better  of  the  two,  as 
it  does  not  clog  the  spraying  machine  when  the  solution  becomes 
cold. 

It  is  usually  necessary  to  know  only  three  constituents  of  a  soap 
in  order  to  judge  of  its  value  for  spraying  purposes,  namely: 
moisture,  total  fatty  matter,  and  total  soda  or  potash.  The  mois- 
ture and  alkali  are  usually  determined  and  the  total  fatty  matter 
approximately  estimated  by  difference. 

Following  are  the  methods  of  analysis  usually  employed:17 
Moisture. — Tare  accurately  a  100  cubic  centimeter  beaker,  the 
17  Bureau  of  Chemistry,  Bulletin  107,  1907  :  31. 


CAUSTIC   SODA  AND  POTASH  641 

bottom  of  which  is  covered  about  one-half  inch  deep  with  recent- 
ly ignited,  perfectly  dry  sand,  and  in  which  is  a  small  glass  rod. 
Place  in  the  beaker  about  five  grams  of  the  sample;  add  25 
cubic  centimeters  of  alcohol  or  more  if  necessary,  and  dissolve 
the  soap  in  the  alcohol  by  constant  stirring  on  the  water  bath. 
Evaporate  the  alcohol  and  finally  dry  in  an  oven  at  110°  until 
the  weight  is  constant.  A  few  precautions  should  be  taken  which 
are  not  mentioned  in  the  above  method,  namely :  If  the  soap  is 
hard  the  five  grams  should  be  cut  off  in  very  thin  strips  so  that 
it  will  dissolve  more  readily  in  the  alcohol ;  also  most  samples  of 
soap  never  come  to  a  constant  weight  on  drying,  but  gain  or 
lose  nearly  indefinitely.  It  is,  therefore,  best  to  heat  the  soap 
at  110°  until  it  is  nearly  dry  and  weigh,  then  return  the  soap  to 
the  oven  and  dry  another  half  hour.  Continue  this  alternate 
drying  and  weighing  until  the  weight  changes  only  a  few  milli- 
grams during  the  course  of  a  half  hour's  drying. 

Total  Alkali.18 — Dissolve  a  weighed  quantity  of  the  soap  in 
water;  decompose  with  hydrochloric  acid,  filter  off  the  water 
from  the  fat,  and  wash  with  cold  water.  Determine  both  po- 
tassium and  sodium  in  the  filtrate  first  as  mixed  chlorids  in  the 
ordinary  manner  and  then  determine  the  potassium  by  means  of 
platinum  chlorid. 

A  rapid  but  only  approximate  determination  of  the  alkali  in 
soap  is  made  in  the  following  manner:  Weigh  a  small  quan- 
tity of  the  soap,  treat  with  concentrated  sulfuric  acid,  burn,  re- 
peat treatment  with  sulfuric  acid,  and  burn  again.  Add  a  small 
amount  of  ammonium  carbonate  to  the  dish,  cover;  and  heat. 
Repeat  this  a  number  of  times  till  all  bisulfates  have  changed 
to  sulfates.  Test  the  residue  qualitatively  to  determine  whether 
it  is  sodium  or  potassium  sulfate,  and  calculate  the  residue  to 
soda  or  potash,  as  the  case  may  be. 

537.  Caustic  Soda  and  Potash. — These  two  substances  are  some- 
times used  in  water  solutions  as  winter  washes.     They  are  more 
often  used  by  the  entomologist,  however,  in  preparing  resin  and 
fish  oil  soaps,  lye-sulfur  mixtures,  etc.     To  judge  of  their  value 
for  any  of  the  above  purposes  and  to  calculate  how  much  of 
18  Bureau  of  Chemistry,  Bulletin  107,  1907  :  31. 
21 


642  '  AGRICULTURAL  ANALYSIS 

the  caustic  soda  or  potash  should  be  used,  it  is  necessary  to  know 
the  carbonate  and  hydroxid  content. 

Following  are  the  methods  usually  employed  in  examining  this 
class  of  goods: 

Carbonate  and  Hydroxid.  Method  7.19 — Solutions  Required. — 
A  half -normal  solution  of  hydrochloric  acid;  methyl  orange  and 
phenolphthalein  indicators. 

Determination. — Weigh  a  large  quantity  of  the  sample  from  a 
weighing  bottle,  dissolve  in  carbon  dioxid-free  water,  and  make 
up  to  a  definite  volume.  Analyze  aliquots  of  this  solution.  Ti- 
trate one  portion  with  half-normal  acid,  using  methyl  orange  as 
indicator,  and  note  the  total  alkalinity  thus  found.  Transfer 
another  aliquot  of  the  same  size  to  a  measuring  flask  and  add 
enough  barium  chlorid  to  precipitate  all  carbonate,  avoiding  any 
unnecessary  excess.  Make  the  volume  up  to  the  mark  with  car- 
bon dioxid-free  water,  stopper,  shake,  and  set  aside  to  allow  the 
precipitate  to  settle.  When  the  liquid  becomes  clear,  draw  off 
one-half  by  means  of  a  pipette  and  titrate  with  half-normal  hy- 
drochloric acid,  using  phenolphthalein  as  indicator.  This  num- 
ber of  cubic  centimeters  of  half-normal  acid  multiplied  by  two 
gives  the  number  of  cubic  centimeters  of  half-normal  acid  cor- 
responding to  the  original  amount  taken.  The  last  figure  ob- 
tained represents  sodium  or  potassium  hydroxid  and  the  differ- 
ence between  the  first  and  last  figures  represents  the  sodium  or 
potassium  carbonate. 

Carbonate  and  Hydroxid.  Method  //.20 — Solutions  Required. 
— A  fifth-normal  solution  of  potassium  acid  sulfate;  methyl 
orange  and  phenolphthalein  indicators. 

•  Determination. — Dilute  with  carbon  dioxid-free  water  an  ali- 
quot of  the  solution  as  prepared  in  Method  I  and  add  a  few  drops 
of  phenolphthalein.  Add  a  fifth-normal  solution  of  potassium 
acid  sulfate  at  the  rate  of  about  one  drop  per  second,  with  con- 
stant stirring,  until  the  pink  color  fades  out  and  the  solution  be- 
comes colorless.  The  reading  thus  obtained  (n)  represents  the 
sodium  or  potassium  hydroxid  and  one-half  of  the  sodium  or  po- 
tassium carbonate  present,  since  the  sodium  or  potassium  car- 

19  Bureau  of  Chemistry,  Bulletin  107,  1907  -.31. 
10  Bureau  of  Chemistry,  Bulletin  107,  1907  :  32. 


UME-SULFUR-SALT     MIXTURE  643 

bonate  is  changed  to  sodium  or  potassium  bicarbonate.  Add 
methyl  orange  and  continue  the  titration  to  the  appearance  of 
a  pink  color.  This  reading  (m)  represents  the  sodium  or  po- 
tassium bicarbonate  present  or  one-half  of  the  sodium  or  potas- 
sium carbonate ;  2m  represents  all  the  sodium  or  potassium  car- 
bonate present,  and  n-m  the  sodium  or  potassium  hydroxid. 

538.  Discussion  of  Methods  of  Analysis    of   Caustic    Soda   and 
Potash. — By  Method  I  higher  results  are  always  obtained  for- 
soclium  hydroxid  than  by  Method  II,  while  by  Method  I  lower 
results  are  always  obtained  for  sodium  carbonate  than  by  Meth- 
od II.     Although  Method  II   is   somewhat  more  difficult  than 
Method  I  because  of  the  great  care  necessary  in  reading  the  two 
end  points,  Haywood  is  inclined  to  think  that  it  is  somewhat  more 
accurate  for  the  following  reasons :     In  Method  I  after  the  car- 
bonates are  precipitated  out  by  barium  chlorid,  the  supernatant 
liquid  is  titrated  for  the  hydroxid  present.     Since  barium  car- 
bonate is  soluble  to  quite  an  extent  in  water  that  portion  which  is 
soluble  is  also  titrated  as  hydroxid,  thus  increasing  the  hydrox- 
id figure.     In  Method  II  all  the  hydroxid  and  one-half  the  car- 
bonate are  first  titrated,  then  the  other  half  of  the  sodium  car- 
bonate, so  there  does  not  seem  to  be  the  same  chance  of  error. 

539.  Lime-Sulfur-Salt  Mixture. — The   lime-sulfur-salt   mixture 
or  simply  the  lime-sulfur  mixture  without  the  salt  is  very  large- 
ly used  in  this  country  against  the  San  Jose  scale.     On  account 
of  the  trouble  incident  to  its  home  preparation   it  has  of  late 
years  appeared  on  the  American  market  in  a  concentrated  form. 
The  chemist  is  often  called  upon  to  examine  this  concentrated 
mixture  in  order  that  the  entomologist  may  calculate  the  proper 
dilution. 

It  has  been  shown  by  Haywood  that  the  liquid  portion  of  the 
lime-sulfur-salt  wash,  which  is  the  portion  sold  on  the  market, 
when  prepared  by  any  of  the  formulas  ordinarily  employed,  con- 
sists principally  of  sulfids  and  polysulfids  together  with  a  moder- 
ately large  quantity  of  thiosulfates  and  very  small  quantities  of 
sulfates  and  sulfites.21  It  is  therefore  necessary  to  make  the  fol- 
lowing determinations  on  a  commercial  sample  of  the  lime-sul- 
"  Bureau  of  Chemistry,  Bulletin  101,  1907. 


644  AGRICULTURAL  ANALYSIS 

fur-salt  wash :  Total  sulfur,  sulfur  as  sulfids  and  polysulfids,  sul- 
fur as  thiosulfates,  sulfur  as  combined  sulfates  and  sulfites,  and 
calcium  oxid.  Following  are  methods  of  analysis  which  give 
good  results : 

Total  Sulfur.22 — Solutions  Required. —  (a)  A  saturated  potas- 
sium hydroxid  solution  or  a  solution  of  sodium  hydroxid  con- 
taining 100  grams  to  100  cubic  centimeters  of  water;  (b)  A  10 
per  cent,  barium  chlorid  solution;  (c)  An  approximately  three 
per  cent,  solution,  of  hydrogen  peroxid  free  from  sulfates.  If 
the  solution  contains  sulfates  add  freshly  precipitated  barium 
carbonate  and  shake  occasionally  for  several  hours,  then  filter 
and  use  the  clear  solution. 

Determination. — Place  10  cubic  centimeters  of  the  clear 
sample  in  a  100  cubic  centimeter  measuring  flask  and  fill  to  the 
mark.  Analyze  10  cubic  centimeter  aliquots  of  this  solution. 
Treat  with  three  cubic  centimeters  of  the  caustic  potash  or  soda 
solution,  following  by  50  cubic  centimeters  of  hydrogen  peroxid 
free  from  sulfates.  Heat  on  the  steam  bath  for  one-half  hour 
exactly  and  then  acidify  with  hydrochloric  acid,  precipitate  with 
barium  chlorid  in  the  usual  way  in  boiling  solution,  and  finally 
weigh  as  barium  sulfate. 

Sulfur  as  Sulfids  and  Polysulfids.23 — Solutions  Required. — The 
same  solutions  are  required  as  are  used  in  the  above  determina- 
tions with  the  following  addition : 

Ammoniacal  zinc  chlorid  solution. — Dissolve  3.253  grams  of 
pure  zinc  in  hydrochloric  acid,  supersaturate  with  ammonia 
and  make  up  to  a  liter. 

Determination. — Pipette  10  to  25  cubic  centimeters  of  the  liquid 
portion  of  the  wash  into  a  100  cubic  centimeter  flask  and  make 
up  to  the  mark.  Use  10  cubic  centimeters  of  this  representing 
one  to  2.5  cubic  centimeters  of  the  original  solution,  for  analysis. 
Add  the  ammoniacal  zinc  chlorid  solution  until  slightly  in  excess, 
as  shown  by  the  reaction  of  a  drop  of  the  solution  with  nickel  sul- 
fate. Place  on  the  steam  bath  and  heat  until  the  odor  of  ammonia 
becomes  faint,  filter,  and  wash.  Transfer  filter  and  contents  to 
a  beaker,  add  about  10  to  15  cubic  centimeters  of  a  saturated 

n  Avery,  Bureau  of  Chemistry,  Bulletin  90,  1905  :  105. 
n  Hay  wood,  Bureau  of  Chemistry,  Bulletin  101,  1907  :  9. 


LIME-SULFUR-SALT     MIXTURE  645 

solution  of  potassium  hydroxid,  and  heat  for  some  time.  Add 
50  cubic  centimeters  of  hydrogen  dioxid,  free  of  sulfates,  and 
heat  on  the  steam  bath  exactly  30  minutes.  Acidify  with  hydro- 
chloric acid  and  precipitate  with  barium  chlorid  in  the  usual 
way. 

Sulfur  as  Thiosulfates. — Solutions  Required.— Ammoma.cd.1  zinc 
chlorid  prepared  as  in  the  previous  method,  tenth-normal  hy- 
drochloric acid,  and  tenth-normal  iodin  prepared  in  the  usual 
way. 

Determination. — Pipette  five  cubic  centimeters  of  the  original 
solution  into  a  50  cubic  centimeter  flask  and  add  ammoniacal  zinc 
chlorid  until  it  is  slightly  in  excess,  as  shown  by  nickel  sulfate. 
Make  this  mixture  up  to  the  mark,  shake,  and  filter  off  through  a 
dry  filter.  To  a  25  cubic  centimeter  aliquot  of  the  filtrate  add 
methyl  orange  and  titrate  with  tenth-normal  hydrochloric  acid  to 
exact  neutrality.  Next  titrate  the  liquid  with  a  tenth-normal  io- 
din solution.  The  reading  thus  obtained  gives  the  total  thio- 
sulfates  and  sulfites ;  since,  however,  the  sulfites  are  present  in 
such  small  amounts  as  to  be  negligible  the  number  of  cubic  cen- 
timeters of  iodin  solution  used  may  be  considered  to  represent 
only  the  thiosulfates. 

Sulfur  as  combined  sulfates  and  sulfites.24 — Solutions  Required. 
— The  same  solutions  are  used  as  are  described  in  the  preceding 
method  with  the  addition  of  10  per  cent,  barium  chlorid. 

Determination. — Follow  the  preceding  method  to  the  point 
where  the  thiosulfates  have  been  changed  to  tetrathionates,  and 
sulfites  to  sulfates  by  the  addition  of  tenth-normal  iodin.  Make 
slightly  acid  with  hydrochloric  acid  and  precipitate  the  combined 
sulfates  and  sulfites  (now  sulfates)  with  barium  chlorid  in  the 
usual  way. 

Lime.2S — Solutions  Required. — Alkali  and  hydrogen  peroxid 
solutions  prepared  as  described  under  total  sulfur.  Also  a  so- 
lution of  ammonium  oxalate. 

Determination. — Proceed  as  in  the  method  for  determining  to- 
tal sulfur  to  the  point  where  all  sulfur  has  been  oxidized  and 

14  Haywood,  Bureau  of  Chemistry,  Bulletin  101,  1905  :  9. 

15  Avery,  Bureau  of  Chemistry,  Bulletin  90,  1905  :  105. 


646  AGRICULTURAL  ANALYSIS 

the  solution  is  acid.  Then  add  ammonia  in  slight  excess  and 
filter  if  a  precipitate  appears.  Determine  the  lime  in  the  filtrate 
by  precipitating  with  ammonium  oxalate  and  finally  weighing  as 
calcium  oxid. 

540.  Kerosene  Emulsion. — In  kerosene  emulsions  as  usually  pre- 
pared the  emulsifying  agent  is  soap.     On  account  of  the  trouble 
of  preparing  these  mixtures  at  home,  various  kerosene  emulsions 
in  a  concentrated  form  have  appeared  upon  the  market  in  late 
years.     In  determining  the  value  of  an  emulsion  of  this  kind  it 
is  usually  only  necessary  to  determine  the  amount  of  kerosene 
present.     A  centrifugal  method  has  been  worked  out  by  Colby 
which  seems  to  give  very  excellent  results.20 

Kerosene. — Weigh  six,  nine,  or  even  18  grams  according  to 
the  strength  of  the  kerosene  emulsion,  and  measure  in  cubic 
centimeters  at  15.5°  into  a  babcock  cream  bottle,  graduated 
to  35  or  50  per  cent.  To  this  add  three  or  four  cubic 
centimeters  of  strong  sulfuric  acid  and  twirl  one  minute 
in  a  babcock  machine;  then  add  cold  water  and  twirl  again  one 
minute ;  finally  add  water  sufficiently  to  bring  the  water  to  or 
above  the  zero  mark  in  the  neck  of  the  babcock  bottle ;  read  the 
cubic  centimeters  of  kerosene  at  15.5°.  Calculate  the  volume 
percentage  of  kerosene  on  the  number  of  cubic  centimeters  of 
emulsion  used  in  the  test. 

541.  Tobacco  and  Tobacco  Extract. — Decoctions  of  tobacco  and 
diluted  tobacco  extracts  are  often  used  against  external  sucking 
insects.     They  are  valued  by  the  entomologist  for  the  amount  of 
nicotin  which  they  contain,  hence  this   is  the  only   determina- 
tion necessary  in  analyses  of  such  articles.     The  Association  of 
Official  Agricultural  Chemists  has  made  careful  studies  of  the 
Lloyd  and  Winton  methods  of  determining  nicotin,  but  unsatis- 
factory results  were  obtained.27     The  only  method  that  has  given 
satisfactory  results,  is  that  of  Kissling.     The   Emery  method, 
tested  by  the  association  in  1904,  appeared  to  lead  to  fairly  sat- 
isfactory results. 

28  Bureau  of  Chemistry,  Bulletin  105,  1907  :  165. 

17  Bureau  of  Chemistry,  Bulletin  56,  1899  :  114,  125  ;    Bulletin  73,  1903  : 
165;  Bulletin  81,  1904  :  203. 


TOBACCO    AND    TOBACCO    EXTRACT  647 

Nicotin.  Method  7.28 — Solutions  Required. —  (a)  Alcoholic  soda. 
— Dissolve  six  grams  of  sodium  hydroxid  in  40  cubic  centime- 
ters of  water  and  60  cubic  centimeters  of  90  per  cent,  alcohol. 

(b)  Sodium  hydroxid. — Dissolve     four     grams     of     sodium 
hydroxid  in  1,000  cubic  centimeters  of  water. 

(c)  Sulfuric  acid. — A  standard  solution. 

Determination. — Place  from  five  to  six  grams  of  tobacco  ex- 
tract or  20  grams  of  finely  powdered  tobacco,  which  has  been 
previously  dried  at  60°  so  as  to  allow  it  to  be  powdered,  in  a 
small  beaker.  Add  10  cubic  centimeters  of  the  alcohol-soda  so- 
lution and  follow,  in  the  case  of  the  tobacco  extract,  with  enough 
chemically  pure  powdered  calcium  carbonate  to  form  a  moist  but 
not  lumpy  mass.  Mix  the  whole  thoroughly.  Transfer  this  to 
a  soxhlet  extractor  and  exhaust  for  about  five  hours  with  ether. 
Evaporate  the  ether  at  a  low  temperature  by  holding  over  the 
steam  bath,  and  take  up  the  residue  with  50  cubic  centimeters 
of  the  dilute  sodium  hydroxid  solution.  Transfer  this  residue 
by  means  of  water  to  a  kjeldahl  flask,  capable  of  holding  about 
500  cubic  centimeters  and  distil  in  a  current  of  steam,  using  a 
condenser  through  which  water  is  flowing  rapidly.  Use  a  three- 
bend  outflow  tube,  a  few  pieces  of  pumice,  and  a  small  piece  of 
paraffin,  to  prevent  bumping  and  frothing.  Continue  the  dis- 
tillation till  all  the  nicotin  has  passed  over,  the  distillate  usually 
varying  from  400  to  500  cubic  centimeters.  When  the  distilla- 
tion is  complete  only  about  15  cubic  centimeters  of  the  liquid 
should  remain  in  the  distillation  flask.  Titrate  the  distillate 
with  standard  sulfuric  acid,  using  phenacetolin  or  cochineal  as 
indicator.  One  molecule  of  sulfuric  acid  is  equivalent  to  two 
molecules  of  nicotin. 

Nicotin.  Method  II.29 — Render  a  weighed  amount  of  the  sample 
alkaline  with  50  cubic  centimeters  of  approximately  tenth-nor- 
mal soda  and  transfer  to  a  round  bottom  flask  of  about  300  cubic 
centimeters  capacity  with  150  cubic  centimeters  of  distilled  wa- 
ter.    Subject  the  whole  to  distillation  in  a  current  of  steam  in  the 
usual  way  and  make  the  distillate  to  a  volume  of  500  cubic  cen- 
78  Bureau  of  Chemistry,  Bulletin  107,  1907  :  32. 
29  Emery,  Journal  of  the  American  Chemical  Society,  1904,  26  :  1113. 


648  AGRICULTURAL  ANALYSIS 

timeters.  Place  a  portion  of  the  distillate  in  a  40  centimeter 
tube  and  take  a  polariscopic  reading,  calculate  the  result  on  the 
value  of  one  degree  on  the  sugar  scale  as  previously  established 
from  chemically  pure  nicotin.  From  this  calculate  the  percen- 
tage of  nicotin  in  the  weight  of  sample  originally  taken. 

Method  II  for  nicotin  can  only  be  used  by  those  who  have  had 
long  enough  experience  with  the  polariscope  to  make  an  exceed- 
ingly close  reading. 

542.  Potassium  Cyanid. — Potassium  cyanid  is  not  used  by  it- 
self, nor  in  solution  in  water  for  spraying  purposes.     It  is  used 
however  as  a  reagent  in  preparing  hydrocyanic  acid  gas,  which 
in  its  turn  is  of  value  in  destroying  scale  insects,  controlling  in- 
sect pests  in  green  houses  and  cold  frames,  destroying  insects 
and  vermin  in  homes,  etc.     In  examining  this  compound  chem- 
ically it  is  the  amount  of  cyanogen  present  that  is  of  interest 
to  the  entomologist.     A  very  accurate  method  of  determining 
this  constituent  is  given  below. 

Cyanogen.™ — Solutions  Required. — Prepare  a  twentieth-nor- 
mal solution  of  silver  nitrate. 

Determination. — Weigh  a  large  quantity  of  the  sample  from  a 
weighing  bottle,  dissolve  in  water  and  make  up  to  a  definite 
volume.  To  an  aliquot  add  twentieth-normal  silver  nitrate,  a 
drop  at  a  time,  with  constant  stirring,  until  one  drop  produces  a 
permanent  turbidity.  In  calculating  the  results,  one  equivalent 
of  silver  is  equal  to  two  equivalents  of  cyanogen,  according  to 
the  following  equation: 

2KCN+AgNO3=KCN.AgCN-fKNO3. 

543.  Carbon  Disulfid. — The  vapors  of  carbon  disulfid  are  often 
used  to  destroy  such  insects  as  plant  lice  on  melons  and  squash 
vines,  insects   in  granaries,  and  insects  and  vermin  in  homes. 
Special  chemical  methods  for  examining  the  purity  of  this  com- 
pound have  not  been  approved. 

544.  Insecticides   for    Subterranean   Insects. — Insecticides    for 
this  purpose  must  either  be  of  such  a  character  that  they  will  dis- 
solve in  water  and  be  carried  down  to  the  insects  beneath  the 
ground,  or  must  be  volatile,  so  that  they  will  smother  the  insects. 

80  Bureau  of  Chemistry,  Bulletin  107,  1907  :  30. 


FUNGICIDES  649 

Among  the  insecticides  that  are  used  for  this  purpose  are  kero- 
sene emulsions,  potash  fertilizers,  strong  soap,  or  tobacco  washes, 
tobacco  dust,  carbon  disulfid,  etc.  Methods  for  examining  these 
materials,  except  carbon  disulfid,  have  been  given  in  the  pre- 
vious parts  of  this  article.  The  potash  fertilizers  are  examined 
for  potash  by  the  usual  fertilizer  methods. 

545.  Insecticides  for  Insects  Affecting  Stored  Grains  and  Other 
Stored  Products. — While  there  are  a  number  of  important  reme- 
dial measures  against  insects  in  stored  products,  such  as  agita- 
tion of  the  grain,  heating,  etc.,  the  only  important  insecticide 
that  is  necessary  to  consider  in  this  connection,  is  carbon  disul- 
fid.    As  has  previously  been  mentioned,  special  chemical  meth- 
ods   for   testing   the   purity  of  this   compound   have   not  been 
proposed. 

546.  Insecticides  for  Animal  Parasites. — Among  the  most  im- 
portant insecticides  of  this  class  are  tobacco  extracts,  lime-sulfur 
mixtures  and  creosote  dips.     There  are  of  course  other  remedies, 
but  not  any  that  the  chemist  will  be  called  upon  to  examine  with 
anything  like  the  frequency  that  he  is  called  on  to  examine  the 
three  classes  of  insecticides  mentioned  above.     Methods  for  ex- 
amining tobacco  extracts  and  lime-sulfur  mixtures  have  already 
been  given.     For  examining  creosote  dips,  the  method  given  by 
Allen  is  usually  followed.     This  method  is  far  from  perfect  and 
gives  only  approximate  results.81 

547.  Fungicides. — Among  substances  that  are  used  as  fungi- 
cides,   or    as    ingredients    in    making    insecticides,    the    chem- 
ist    is     most    often    called    upon    to    examine    the    following: 
Bordeaux  mixture,  copper  sulfate,   copper  carbonate,  lime-fer- 
rous sulfate,  sulfur  and  formaldehyde  solutions.     Methods  for 
examining  the  first  six  of  these  are  based  on  general  principles 
and  are  so  self-evident  that  it  does  not  seem  necessary  to  mention 
them.     It  may  be  said,  however,  in  passing,  that  the  Association 
of  Official  Agricultural  Chemists  has  adopted  official  methods 
for  determining  copper  in  copper  carbonate.32 

81  Allen,  Commercial  Organic  Analysis,  3rd  Edition,  1907,  2,  Part  2  :  262. 

Bureau  of  Chemistry,  Bulletin  90,  1905  :  103. 
3J  Bureau  of  Chemistry,  Bulletin  107,  1907  :  30. 


650  AGRICULTURAL  ANALYSIS 

For  determining  formaldehyde  in  solutions  of  this  substance 
the  following  methods  are  commonly  used: 

Formaldehyde.  Method  7.33 — Solutions  Required. — A  normal 
solution  of  sulfuric  acid,  a  normal  solution  of  sodium  hydroxid 
and  a  solution  of  purified  litmus. 

Determination. — Place  50  cubic  centimeters  of  normal  sodium 
hydroxid  in  a  500  cubic  centimeter  erlenmeyer  flask  and  add  50 
cubic  centimeters  of  hydrogen  dioxid.  Then  add  three  cubic 
centimeters  of  the  formaldehyde  solution  under  examination  (the 
specific  gravity  of  which  has  been  previously  determined),  allow- 
ing the  point  of  the  pipette  to  almost  reach  the  liquid  in  the  flask. 
Place  a  funnel  in  the  neck  of  the  flask  and  put  on  the  steam  bath 
for  five  minutes,  shaking  occasionally  during  this  time.  Remove 
from  the  steam  bath,  wash  the  funnel  with  distilled  water,  cool 
the  flask  to  about  room  temperature,  and  titrate  the  excess  of 
sodium  hydroxid  with  normal  acid,  using  litmus  as  indicator. 
This  cooling  of  the  flask  before  titration  with  acid  is  necessary 
in  order  to  get  a  sharp  end  reading  with  the  litmus.  From  the 
volume  of  formaldehyde  used  and  the  specific  gravity  determine 
the  per  cent,  of  formaldehyde. 

Formaldehyde.  Method  II.34 — Solutions  Required. — Double 
normal  sodium  hydroxid  and  double  normal  sulfuric  acid. 

Determination. — Place  three  grams  of  the  solution  in  a  tall 
erlenmeyer  flask  containing  25  to  30  cubic  centimeters  of  double 
normal  sodium  hydroxid.  Then  gradually  add  50  cubic  cen- 
timeters of  pure  2.5  to  three  per  cent,  hydrogen  peroxid  during 
a  space  of  three  minutes  through  a  funnel  placed  in  the  neck  of 
the  flask  to  prevent  spurting.  After  standing  two  or  three  min- 
utes, wash  the  funnel  with  water  and  titrate  the  unused  sodium 
hydroxid  with  double  normal  sulfuric  acid,  using  litmus  as  in- 
dicator. 

When  analyzing  solutions  containing  less  than  30  per  cent,  of 
formaldehyde,  the  mixture  must  be  allowed  to  stand  10  minutes 
after  adding  the  hydrogen  peroxid  to  complete  the  reaction. 

J3  Haywood  and  Smith,    Journal   of  the   American   Chemical   Society, 
1905,  27  :  1183. 

84  Bureau  of  Chemistry,  Bulletin  107,  1907  :  33. 


FUNGICIDES  651 

Find  the  percentage  of  formaldehyde  by  multiplying  by  two 
the  number  of  cubic  centimeters  of  soda  solution  used,  when 
three  grams  of  substance  are  examined. 

Acetaldehyde  reacts  much  more  slowly  with  the  reagent  than 
formaldehyde,  and  it  is  doubtful  whether  the  reaction  is  quanti- 
tative. 

Paraldehyde  reacts  still  more  slowly  with  hydrogen  peroxid, 
even  in  the  presence  of  a  trace  of  ferrous  salt.  Benzaldehyde  is 
acted  upon  more  quickly,  particularly  in  presence  of  ferrous  sul- 
fate,  and  a  considerable  evolution  of  gas  takes  place,  but  a  long 
time  is  needed  to  complete  reaction. 

Formaldehyde.  Method  III.35 — This  method  is  to  be  used  es- 
pecially in  solutions  containing  a  small  amount  of  formaldehyde. 

Solutions  Required. —  (a)  Silver  nitrate. — A  tenth-normal  so- 
lution. 

(b)  Ammonium  sulfocyanate. — A  tenth-normal  solution. 

(c)  Potassium  cyanid. — A  solution  containing  3.1   grams  to 
500  cubic  centimeters  of  water. 

(d)  Nitric  acid. — A  50  per  cent,  solution. 

Determination. — Treat  15  cubic  centimeters  of  the  silver  ni- 
trate with  six  drops  of  50  per  cent,  nitric  acid  in  a  50  cubic  cen- 
timeter flask;  add  10  cubic  centimeters  of  the  solution  of  potas- 
sium cyanid  and  shake  well.  Then  make  the  solution  up  to  the 
mark  and  titrate  an  aliquot  of  the  filtrate  (say  25  cubic  centi- 
meters) with  tenth-normal  solution  of  ammonium  sulfocyanate 
for  the  excess  of  silver.  Acidify  another  15  cubic  centimeter 
portion  of  tenth-normal  silver  nitrate  with  six  drops  of  50  per 
cent,  nitric  acid  and  treat  with  10  cubic  centimeters  cf  the  potas- 
sium cyanid  solution  to  which  has  been  added  a  weighed  quan- 
tity of  the  dilute  formaldehyde  solution.  Make  up  the  whole 
to  50  cubic  centimeters  and  titrate  a  25  cubic  centimeter  filtrate 
from  it  with  tenth-normal  ammonium  sulfocyanate  for  the  excess 
of  silver  as  before.  The  difference  between  these  results  multi- 
plied by  two  gives  the  amount  of  potassium  cyanid  that  has  been 
used  by  the  formaldehyde  in  terms  of  tenth-normal  ammonium 
sulfocyanate.  Each  cubic  centimeter  of  this  is  equivalent  to 
three  milligrams  of  formaldehyde. 

85  Romijn,  Zeitschrift  fiir  analytische  Chemie,  1897,  36  :  18. 


652  AGRICULTURAL   ANALYSIS 

548.  Discussion  of  Methods  of  Analysis  of  Formaldehyde  Solu- 
tions.— Method  I  has  been  carefully  tested  and  has  been  found 
to  give  excellent  results  on  strong  solutions  of  formaldehyde. 
Method  II,  the  original  hydrogen  peroxid  method,  gives  results 
that  are  slightly  below  the  truth.  The  reasons  for  the  superior- 
ity of  Method  I  over  Method  II  has  been  explained  by  Haywood 
and  Smith.38  Method  III  has  been  carefully  tested  and  has  been 
found  to  give  good  results.     It  can,  however,  only  be  used  on 
dilute  solutions  of  formaldehyde,  or  on  concentrated  solutions, 
which  are  diluted  to  a  large  extent.     Since  the  error  of  analysis 
would  be  greatly  multiplied  by  examining  concentrated  solutions 
of  formaldehyde  by  this  method  it  seems  best  to  restrict  it  to 
solutions  that  are  dilute  in  the  beginning. 

549.  Statement  of  Insecticide  Analyses. — Two  typical  insecti- 
cides may  be  considered  in  presenting  a  scheme  for  expressing 
the  results  of  analyses,  namely,  paris  green  and  london  purple. 
In  making  complete  analyses  of  paris  green  the  following  con- 
stituents should  be  determined,  namely,  moisture,  sand,  sulfur 
trioxid,  copper,  total  arsenic,  soluble  arsenic,  and  acetic  acid. 

It  is  best  to  report  the  sulfur  trioxid  in  the  form  of  sodium 
sulfate,  since  from  the  method  of  manufacture  of  paris  green  it 
is  almost  certain  that  the  sulfur  trioxid  present  exists  in  this 
form  in  the  green.  The  copper  should  be  reported  as  cupric 
oxid  (CuO),  and  the  total  arsenic  as  arsenic  trioxid  or  arsenious 
oxid.  The  acetic  acid  present  should  not  be  reported  as  acetic 
acid  as  is  usually  done,  but  as  acetic  anhydrid,  since  the  report- 
ing of  the  copper  as  CuO  has  left  the  acetic  acid  as  acetic 
anhydrid. 

In  reporting  soluble  arsenic  it  should  be  given  as  arsenious  oxid 
or  arsenic  trioxid  and  should  be  determined  in  two  ways;  (i) 
by  the  Avery-Beans  method  to  approximately  determine  the  actual 
free  arsenious  oxid  present,  and  (2)  by  the  prolonged  water 
soluble  method  to  determine  to  some  extent  the  stability  of  the 
green. 

In  examining  samples  of  london  purple  the  following  deter- 
minations should  be  made,  moisture,  insoluble  in  hydrochloric 
M  Journal  of  the  American  Chemical  Society,  1905,  27  :  1183. 


STATEMENT    OF    INSECTICIDE    ANALYSES  653 

acid,  total  and  soluble  ic  arsenic,  total  and  soluble  ous  arsenic, 
calcium  and  dye  by  difference.  The  ic  arsenic  in  both  cases 
should  be  reported  as  arsenic  pentoxid  and  the  ous  arsenic  as  an 
arsenic  trioxid.  The  calcium  should  be  reported  as  calcium  oxid. 
The  words  "by  difference"  should  always  follow  the  dye  figure. 

SCHEME  FOR  REPORTING  RESULTS  OF  ANALYSES 

PARIS  GREEN 

Moisture % 

Sand 

Sodium  sulfate  •  •  •    

Total  arsenious  oxid 

Total  copper  oxid 

Acetic  anhydrid 

Total 

Soluble  arsenious  oxid  by  Avery-Beans  Method % 

Soluble  arsenious  oxid  by  water  extraction  method 

LONDON  PURPLE 

Moisture % 

Insoluble  in  hydrochloric  acid 

Total  arsenic  oxid 

Total  arsenious 

Calcium  oxid 

Dye  (by  difference) 

Total 

Soluble  arsenic  oxid • 

Soluble  arsenious  oxid 

Soluble  calcium  oxid 


INDEX    OF    AUTHORS 


Aitken    519 

Albert     180,  568 

Allen      259 

Andrews     573 

Asboth •. 347,    352,    356,    373,  374 

Atwater    291 

Auriol     44* 

Avery    630,   644,   645,  652 

B 

Battle   337 

Beans    630,  652 

Beck   437. 

Berju     125 

Berthelot      319 

Bertrand    578 

Berzelius    262,  57,1 

Bessemer     192 

Bieler    91,    199,   358,   397,  435,  54$ 

Birkeland 310,     314,  318 

Blair 167,     173,     176,  173 

niattner    252,    254,  391 

Blum      219 

Bonnema     3°2 

Bernstein     337 

Bottcher    68,   209,   210,   211,   212,   213,   214,  222 

Boussingault    129,    292,    384,  423 

Boyer   33§ 

Bradley    310,  313 

Brasseur      252,     254,  391 

Brown      244 

Bryant     1 57 

Biihring     91 

Burchard     600 

Burk     26j 

C 

Campbell 259 

Carnot    254,    267,   271,  272 

Caro     3°6 

Cart    3°9 

Caspar!    580,    583,    586,    587,    588,    589,  592 

Cathcart    630 

Chabrier    474 

Chancel     254 

Charlton      3°7 

Chatard   224,  228,  238,  262,  264 

Chevreul    26,  578 

Clarke     266,  573 


656  INDEX   OP  AUTHORS 

Classen    218 

Cohen     449 

Cohn     •„ no 

Colby .' 630,  633,  646 

Contamine     544 

Corenwinder 544 

Cornu     544 

Crawley    283,  284 

Crispo    237,    238,  424 

Crookes    109,  310 

Crum 413 

Cushman  518,  520,  521,  522,  523 

D 

Dabney    1 10,  608 

Dafert    352 

Dagnino     295 

Dall    31 

Dana    26 

Dancy    337 

Darton     28 

Day    157 

Delatre      252 

Delaunay     487 

Devarda    389.  438 

Deventer     477 

Drown    258 

Dudley  and  Noyes   131.  168 

Dudley    131,  169 

Dumas     578 

Dyer    285,  533 

E 

Eldridge    29,    30,    31 

Emery     646 

Emmerton     131,  168 

Erlwein     310,  312 

Eyde    314,  318 

R 

Le   Feuvre    295 

Fperster     378 

Forchhammer     289 

Forster 220 

Frank   3°6 

Frankland   413 

Fraps      622 

Fresenius    67,    no,    in,   247,  355 

Freudenberg   3 1 2 

Fricke     444 

Fuchs    295,  487 

O 

Gabriel     273 

Gautier    25 

Gerhardt    187,  189 

Gerlach    307 

Gibba      152 

Gilbert   273,  274 


INDEX   OF   AUTHORS  657 

Gilchrist     192 

Gill     461 

Girard i°8,  544 

Gladding    129,  253 

Gladstone      449 

Glaser   ...67,  72,  89,  98,  166,  228,  231,  234,  236,  237,  238,  241,  244,  247,  252,  253,  254 

Goessmann    289,  529 

Gooch    225,  453 

Goode     291 

Goutal     271 

Graftiau     127 

Grandeau    308,    341,    389,    544,  578 

Gray     448 

Griess     465,  468 

von    Griiber    237 

Grueber    252,  253 

Gruener     453 

Grupe     89 

Gunning    370,  373 


H 

Haberstadt    

Halenke     

Hall    

Halske     

Hanamann    122, 

Harcourt     

Hare 

Hartwell     

Harvey     • 

Hayes   32,  36 

Hay  wood 627,  628,  629,  630,  632,  633,  637,  638,  643,  644,  645 

Headden    520 

Heintz     152 

Hensel     520 

Hess    232,    233,    234,    244,  259 

Hilgard     216,    569,  602 

Hillebrand    266 

Hollemann    178,  218 

Holverscheit     276 

Hooker    45$,  461 

Hopkins     623 

Horsin-Deon   534 

Howies     3i8 

Humboldt    292 

Hundeshagen    123,  125 

Huston    47,   no,   112,   115,   119,   202,   217,  564 

Hyde    130 


Ilosvay     484 

Immendorff      229 


658  INDEX   OP  AUTHORS 

J 

Jatnieson    303,  304 

Jenkins 289,    329,  331 

Jensch     220,  221 

Jodlbauer    347,    356,  374 

Joffre     284 

Johnson 90,     102,    329,     331,  464 

Jones   67,  217,  218,  228,  236,  237,  238,  247 

Jorgensen   81,   82,   104,  105 

Joulie 132,    136,   178,    185,  544 

Jumeau      386 

Tiiptner    65 

K 

Kalmann    166 

Kellner 209,    211,  448 

Kilgore 56,  68,   119,    124  ,131,    157,   158,  159 

Kissling     646 

Kjeldahl 88,    347,    350,    352,  389 

Knorr     225 

de    Koninck    409,  450 

Kormann     196 

Kowalsky    310,  313 

Kraut     578 

Kreider    577,    581,    585,    586,  588 

Krug 195,    241,  244 

Kriiger     446 

Kuss      128 

L_ 

Landolt      337 

Lasne 67,   101,   102,  249,  252,  253,   254,  267,  271,  272 

de   Launay    295 

Leavens     190 

Leavitt     53 

LeClerc     53.  3°6 

I,edoux      119 

Leffmann     461 

Lenglen      3°6 

Lichtschlag     253,  254 

Liebaut    544 

Lindemann     274 

I,indsey     608 

Lipman      305 

Lloyd     646 

Loges     34i 

Long    156 

Lorenz     65,    123,  125 

Lovejoy    31°.  3*3 

Luck     in 

Lunge    415,   465,   473,  560 

Lungwitz     562 

Lwoff    465,  473 

M 

Macf arlane    216 

Mach    213,   214,   215,  216 


INDEX   OF   AUTHORS  659 

Maercker   103,  213,  217,  489,  496,  497,  506 

Magnus     519 

Mamelle     544 

Marcano    292,  293 

Maret   252 

'  Mariano   de   Rivero    293 

Marioni     239 

Marlatt      626 

Marsais    544 

Marx     426 

Mason    472,  484 

McElroy    79,   241,  242,  244,  613 

McGowan    450 

Meinecke     123 

Meissels     1 66 

Millot     136 

Monnier     441 

Monroe      35 

Moore     285,  564 

Morgan    91 

Moscicki     313,  320 

Motteu     152 

Muller     140 

Munro     132 

Miintz    292,    293,    309,  544 

N 

Naumann 206 

Nessler    347,  4«o 

Neubauer    79,    83,    85,    86,    87,    88,    89,    m,  132 

Neuberg     381 

Neumann    S3,    125,    127,  162 

Nihoul     450 

Nollner      295 

Nottin      309 

Noyes      131,  169 

Noyes  and  Dudley   131,  168 

O 

Ogilvie         241 

Oliveri     184 

Ormandy     449 

Osborne     ' 90 

Ostersetzer      189 

Otto     152 

P 

Patrick     368 

Pawling     310 

Pease      169 

Peligot    338,  578 

Pellet 63,    119,  129 

Pemberton 56,   119,   122,   131,   153,   154,   157,  158,  159 

Pennock 297 

Perrot    177 

Peter    378 


660  INDEX   OF   AUTHORS 

Petermann    70,   94,    i  oo,  1 28 

Piccini     466,  477 

Pincus    132 

Pissis 294 

Pratt    28 

Prillieux      544 

Prunet     284 

R 

Rayleigh      310 

Reese    192 

Regel     567 

Reininger      313 

von    Reis    197 

Reitmair     47,     286,  534 

Reynoso     108 

Richters    220.  247 

Rideal    461 

Kisler     544 

Robine     306 

Robinson     570 

de  Roode 62,  539,  563 

Roscoe     579 

Rose     266 

Rosenheim     276 

Ross 63,     64,  107 

Rossler    77,  97 

Royse     169 

Ruffle     343 

Rutnpler     115,  280 


Salberg     69 

Sanborn     61 

Schaeffer     477 

Schenke    213,    214,  215 

Scheuch 219,  599 

Schiff     329 

Schloesing 284,    391,    544,    578,  579 

Schmitt      443 

Schneidewind 91,   199,  358,  397,  435.  54^ 

Schucht     221 

Schweitzer     562 

Scovell    347,   356,   377,    378,  380 

Selckmann     390 

Serullas     578,  579 

Sestini     302 

Sherman     130 

Shutt    307 

Sidersky    72 

Sievert     440 

Smith 627,  652 

Sorauer     191 

Spencer 177,  178 

Squanto     291 


INDEX   OF   AUTHORS  66l 

Stead     '. 254 

Stoklasa    24,  439 

Stone    219,  599 

Street     445 

Stutzer    126,  387 

Sutton    132,   137,  274,  413 


Tasselli    239 

Thibault    341 

Thilo     119,  13' 

Thomas 192 

Thomson     156 

Tilden     450 

Tisserand    544 

Tollens    89 

Tribe    449 

U 

Ulsch    357.  389,  444 


Van    Slyke    ............................................................   371.  373 

van't    Hoff  ..............................................   5°9,    5",    $12,    517,  518 

Varrentrap      ..............................................................  338 

Vassalie're     ...............................................................  544 

Veitch   .............................................   63,  64,  65,  120,  253,  260,  564 

Vogel     ...................................................................  90 

Volhard    ...............................................................    178,  387 

Voorhees    .........................................................  46,    305,  381 


Wagner  ......  65,  67,  68,  114,  126,  185,  186,  200,  201,  202,  207,  210,  214,  215,  216,  218,  247,  341,  592 

Wanklyn     .............................................................  346,  347 

Warington    ............................................................   447,  479 

Wavelet     .................................................................  165 

Weber    ...................................................................  575 

Weitz     ...................................................................  301 

Wells     ...................................................................  90 

Wense     ..................................................................  578 

Wheeler    .................................................................  192 

Wiley    .......................   6,    no,    195,    196,   295,   302,     310,   564,    577,   599,  616 

Wilfarth      ................................................................  356 

Will     ....................................................................  338 

Williams      ................................................................  447 

Winton  ......................................................   381,    571,    572,  646 

Woll    ..............................................................   74,    98,  549 

Woy     .......................................................    123,    124,    125,  130 

Wrampelmeyer  .........................................................   221,  359 

Wyatt   ..............................   26,   27,   28,   225,  227,   229,   243,   264,   266,  282 


INDEIX 


Absorption    towers 3 1 5 

Acetaldehyde    651 

Adulteration  of  basic  slag 221 

Albert,    method    for    phosphoric    acid i  go 

Albuminoid    nitrogen     387 

detection      323 

Alkalies,    early    official    method 616 

estimation    in    ash 615 

Alsace,     potash     deposits 489 

Alumina    and    ferric    oxid,    determination 67 

in  natural  phosphates,   estimation. ..  .253,   254,   255,   256 

257,     258,  259 

iron,    estimation    247 

estimation     in     ash 612 

Richters-Fcrster    method    of    detection     220 

separation  from   iron   by   phenyl-hydrazine 259 

Aluminum    mercury    couple    449 

phosphate ,  adulteration     with 220 

composition     256 

Amid   nitrogen    388 

Ammonia     287 

•albuminoid      483 

determination     383 

method    of    Boussingault    384 

in    rainwater,    determination     448 

salts,    effects    302 

Ammoniacal     nitrogen,     determination     389 

Ammonio-manganous    phosphate,    composition     153 

Ammonium   citrate,    preparation 56 

magnesium    phosphate    solution    138 

nitrate    solution,    preparation     57 

sulfate,  composition  of  commercial   386 

Anhydrite     486 

Apatites,    availability 121 

Aqueous  vapor,  tables  of  tensions 335,   336,  407 

Arsenic    acid,    determination 635 

error  due  to    135 

oxid,    determination 639 

Arsenious   oxid,    determination 627,    628,    629,  634 

Ash    analyses,    statement    of    results 530,  531 

preparation     618 

Ashes,    fertilizing    value 532 

Atmospheric    nitrogen,    fixation    by    electricity 310 

utilization      310 

Availability    of    phosphates,    method    of    determining    285 

Available    phosphoric    acid,    direct    determination     63 


INDEX  663 


Barnyard    manures,     sampling 15 

Barometer,    correction 332,     333,  334 

reading     332 

Basic   phosphatic    slags    190 

slag,    amorphous    195 

availability      191 

citric    acid    extract    205 

composition     195 

crystalline      195 

Dutch  method   for   phosphoric    acid    200 

history   of  manufacture    192 

manufacture  in   the   United   States    192,  193 

mixture   with    other    fertilizers    192 

neutralization  of  basicity   200 

official    methods     216 

preparation    of    citric    acid    extract 206 

process    of    manufacture 193 

superior  -qualities    190 

quantities  manufactured  in   various  countries 193 

used     190 

treatment   of  citric   acid   extract 206 

uses     190 

utility   in  various  crops   and   soils 192 

Wrampelmeyer's   method    for    detecting   adulteration 221 

slags,  Bottcher's  modification   for   determining  phosphoric   acid 215 

conditions   of   accurate  analysis 204 

German    agricultural    experiment    station    method 203,  209 

loss   on   ignition    222 

preparation  of  citric   acid  extract   for  analysis 205 

rich  in  silicic   acid,   official   German   method 209 

Bat     guanos 606 

Beet     molasses,     composition 534 

Benzaldehyde     651 

Bergkieserit      500 

method    of   analysis 550 

Betiiin     289 

Black     alkali 602 

phosphates,     occurrence 33 

Blue    phosphate,    occurrence 41 

Bone   meal,   value   of   denitrogenized 47 

Bordeaux    mixture    649 

Breccia    phosphate 35 

Brucine,    detection    of    nitric    acid 323 

Brussels    congress,    method    for    phosphoric    acid 99,  100 

Biihring,    citrate    method 91,    92,    93,  94 

Bureau   of  Soils  method  of  stating  results  of  analysis 624 

C 

Calcined    manurial    salts,    analysis 558 

Calcium    cyanamid,    manufacture    311 

properties    307,  311 

uses      312 

determination     619 

oxid    determination    637 

salts,  effect  on  the  determination   of  alumina 257 


664  INDEX 

Caliche,     composition     296,  297 

California,    niter    deposits 295,  296 

Canada     ashes 529,  530 

Carbon    dioxid,    determination   in    mineral    phosphates 225 

estimation  in  ash 616,  618 

disulfid      648 

estimation   in   ash    610,   613,  618 

Carbon-free   ash,   determination    617 

Carbonates,    reactions   in  superphosphate   manufacture 279 

Carnallit     486,     487,     491,  493 

composition     494 

description      497 

method    of    analysis 550 

Caustic   lime,    estimation   in   basic   slags 219 

soda  and  potash,  discussion  of  methods  of  analysis 643 

Cave     deposits 606 

Charcoal,    adulteration  'of   basic    slags 221 

Chili   saltpeter,   adulteration    299 

analysis    by    difference 424 

application     300 

commercial     forms 299 

direct    and    indirect   methods    of    analysis 437 

quantities     applied 301 

Chlorid,   influence   on   Hooker's  method    460 

Chlorin,    determination 620 

in    ash     616 

plants   621 

Chlor-platinic    acid,    preparation    by    electrolysis     575,  576 

Cholin     289 

Chromium    in     phosphates     274 

Citrate    and    molybdate    methods 102,  103 

Citrate-insoluble  phosphoric   acid,   official  method 61 

volumetric    method    160 

Citrate  method,   general   principles 88,   89,   90 

ignition   of   the  precipitate    97 

manipulation '.  95 

of  Halle  agricultural  experiment  station 91,  92,   93,  94 

official    Swedish    98 

shaking    apparatus    96 

small    phosphoric    acid    content 105 

solutions    employed    95 

temperature    conditions HI 

precipitate,     purity 104 

Citrate-soluble    phosphoric    acid 100,  101 

direct    precipitation 106,  107 

official    method    62 

Citric    acid,     influence    of    strength     on    digestion 217 

on  precipitation   of   phosphoric   acid 65 

Columbia    niter    deposits 295 

Combustion    furnace    329 

Composition    of    potash    salts,    calculation     553 

Composts     594 

Copper,    determination   in    copper    carbonate 649 

oxid,    determination     631,  632 

nitrogen    determination     323 

Copper-zinc     couple 449 


INDEX  665 

Cottonseed     hulls 528 

meal    287,   289,  528 

ash,     composition 288 

composition ;  288 

Crude    phosphates,    quantities    produced     193 

protein     387 

Crum-Frankland    method,    Warington's    modification 414 

Cupric    hydroxid,    preparation    388 

Cyanamid    compound,    toxic    effect 308 

value  as  fertilizer   307 ,  308 

later     experiments 308,  309 

manufacture     306 

D 

Dall,    origin   of   phosphates 31 

Davidson,   origin   of   Florida   phosphates 26 

Destruction  of  organic  matter,   method  of   Neumann 51,   52 

Devarda,    nitric     acid    method     438 

Digestion    apparatus    for    basic    slags 202 

reverted   phosphates 115,    116,  117 

Diphenylamin,  production  of    colors 466 

Dried  blood    287,  290 

Drying,    general    observations 23 

official     methods 23 

samples      22 

Ducks,     on     Layson     Island 291 

Dudley    and    Noyes    method 1 68 

Dutch    method,    citrate-soluble    phosphoric    acid 100,  101 


Eldridge,    origin    of    phosphates 29,    30,  31 

Emmerton     method 1 68,  1 69 

r 

Feldspar,    conclusions    regarding    use 525,  526 

Cushman's    investigations 520 

grinding     mills 522 

manurial    experiments      519-526 

possible     harmful     effects 524 

production    and    value 524 

results    of    cultural    experiments 522 

Feldspathic    rocks,    potash    from 518 

Ferric    oxid    and    alumina,    determination 67 

catalytic   influence 303 

determination     259 

phosphate,    estimation    in    ash    61 : 

Ferrodur     313 

Ferrous    sulfate    594 

agricultural    uses    603 

analysis      603 

poisonous     properties 603,  604 

Fertilizer  analysis,   advantages  of  elemental   system  of  stating  results 623 

elemental   system  of  stating  results 623 

expressed   as    ions    625 

stating    results     621 


666  INDEX 

Fertilizers,    apparatus    for    crushing i  * 

definition     i 

importations      45 

international   methods    of    determination 66 

miscellaneous,     classification 594 

occurrence     in     nature i 

sampling    of    manufactured 1 1 ,    12 

mixed     13,    14 

valuation    3,   4 

Fertilizing     ingredients,     trade     values 3 

valuation     2 

materials,     prices 3 

waste   matters    as 2 

Fish,     content    of    nitrogen 29 1 

Fixation     of    basic     soils 283 

Flax     seed 288 

Florida   phosphates,    origin    26,    29 

Fluorids,    distinction    between    basic    slags    and    phosphates 222 

treatment    in    mineral    phosphates 278 

Fluorin   and    silica,    loss    in   analysis    227 

effect    on    determination    of    alumina 258 

estimation     247 

Burk's   modification    267 

Carnot's     method     267 

method   of    Geological    Survey 262,    263,    264,    265 

L,asne   267,  268,   269,  270,  27 1 

modified   by    Carnot    27  i 

Rose     266 

modification     of     Wyatt 264 

in     bones 272 

occurrence     in     phosphates 261 

principles    of    estimation 262 

protection     of    glassware     272 

signification      t 261 

test    for    adulteration    of   basic    slags 222 

Formaldehyde,     determination     650 

discussion    of    method    of    analysis    652 

Free    acid,    determination    in    phosphates 187 

in     superphosphates 189 

phosphoric     acid    determination 247 

Fungicides     649 

0 

Gas.    sampling    6,    7 

Grape  pomace    535 

Green    arsenoid     633 

vitriol,     agricultural     uses     603 

Guano    292,  594 

Guanos     606 

estimation   of   phosphoric    acid 607 

Gunning    method 370 

for   nitric    acid    381 

modifications     371 

official      372 


INDBX  667 

Gunning  method,  official,  to  include  nitrates 382 

reactions  37  x 

Gypsum  4g8)  S94 

action  on  black  alkali 602 

analysis  , 600 

composition  602 

consumption  for  agricultural  purposes 600 

solubility  in  sodium  carbonate 60 1 

value  599 

water  of  crystallization 602 

H 

Hair    290,  609 

Halle  station  methods  for  phosphoric  acid  and  basic  slags 199 

Hanamann,    direct    weighing   of   phospho-molybdate    precipitate 122 

Hartsalz    503,  553 

Hayes,    origin    of    white    phosphates 36,    37,    38 

Hen    manure 594 

analysis     606 

properties      605 

Hoof    290 

Horn    290,  609 

Huston,    digestion    apparatus 115,    116,  117 

mechanical     stirrer 118 

solubility   of   phosphates no 

value  of  finely  ground  bone   47 

I 

Ignition   with  sulf uric   acid 538 

Incineration,   loss   of  phosphoric  acid 52,   53 

of    organic    phosphorus,    Leavitt    and    LeClerc's    method S3 

Indigo    method    of    Boussingault 427,  429 

Marx     426 

Warington      429 

solution    preparation    428 

standardization      429 

Indigotin     preparation      43° 

standardization     43' 

Inorganic    plant  constituents,   official   methods   of   determination 617 

lodin    in    phosphates 273 

titration     351 

lodometric    estimation    of    nitrogen 450,    451,    452,  453 

Insect   pests,    classifications 626 

kinds     625 

Insecticide  analysis,  scheme   for   reporting 653 

statement     652 

Insecticides   625 

classification    626 

for  animal   parasites    649 

external    sucking    insects    640 

insects    affecting    stored    grains 649 

subterranean    insects     648 

International    Steel    Standards    Committee,    methods 173 


668  INDEX 

Iron  and  alumina,  comparison   of  methods   of  estimation 252 

compounds,   occurrence   in   phosphates 279 

estimation     247 

in   mineral  phosphates,   acetate   method 231 

estimation    239 

method  of  Eugen  Glaser 234 

Hess   232,  233,  234 

phosphates,    Crispo's  method 237 

method  of  C.  Glaser    231 

Marioni   and    Tasselli    239,  240 

phosphates,    separation    244 

separation,    method   of   Ogilvie 241 

Wyatt's    method     243 

aluminum  disturbing  effects  in  determining  phosphoric  acid 188 

estimation   in  ash    612,  615 

phosphoric    acid    612 

excess    in    estimation    of    phosphoric    acid 167 

function    in    plants    *9i 

influence   on    basic    slag 191 

Hooker's   method    460 

role   in   absorption    of   nitrogen 302 

salts,   effect  on  the  determination  of  aluminum   phosphate 256 

J 

Jodlbauer    method,    Halle    station    376 

royal    Holland    station 375 

Jones   reductor    171 

Jorgensen's   method   of    determining   phosphoric    acid 81,    82,    83 

purity  of  precipitate  with  citrate 1 04 

Juptner,  method  with  tartaric  acid   65 

K 

Kainit,   composition    494 

de    Roode's   method 563 

description     495,  496 

method   of  analysis    550 

Kerosene  emulsion 646 

Kieserit    486 

description      500 

Kjeldahl  method,   digestion   apparatus,   Bureau  of  Chemistry 367 

distillation  apparatus,  Bureau  of  Chemistry 368 

for  nitrates,  official    380 

Gunning   modification    370 

Halle    station    358 

indicator     362 

Holland    station    357 

modification  of  Asboth    373 

Wilfarth    356 

modifications      355 

modified  to  include  nitric    acid 373 

of  determining  nitrogen    347,  355 

official      363 

distillation     367 

manipulation     366 

reagents     365 

preparation   of   reagents    352,  354 


INDEX  669 

Kjeldahl     method,    theory    of    the    reaction     352 

titration   of  iodin   f 350 

variation  of  Jodlbauer 374 

Krug  and  McElroy,   variation   in  alcohol  method   of  separating  lime 241,  242 

Kriiger's  method   for   nitric  acid 446 

Krugit,     description     499 

l_ 

Lamellar    phosphate     35 

Lasne ,    method     i  o  i 

Lead    arsenate,    analysis    > 638 

compound,     estimation    in     phosphoric     acid 165 

oxid,     determination      638 

of   water-soluble    639 

Leather,     waste     608 

Leavitt   and   LeClerc,    incineration   of    organic   phosphorus 53 

Leguminous    plants,    inoculation    3°5 

Lime  action      595-597 

analysis 598 

and    magnesia    in    mineral    phosphates,    estimation    from    lime 244,  245 

application      595 

determination     of     carbonate     188 

estimation    in    ash     6ii,  614 

basic    slag 218 

forms     594,  595 

Glaser-Jones    method     228 

in    mineral    phosphates,     ammonium-oxalate    method 229 

Chatard's  variation  of  the  alcohol  method...   238,  239 

difficulties  of  separation   with   alcohol 234 

estimation  by  method  of  Jones 236 

method    of    Immendorff    229 

separation    with    alcohol      234 

plaster,    value    599 

preferable     forms     597 

shell      594.  597 

state    of    combination     599 

Lime-sulfur-salt    mixture    643 

method    of   analysis    643-646 

sulfur  as  combined   sulfates   and   sulfites 645 

sulfids    and    polysulfids 644 

thiosulfates     645 

total   sulfur    644 

Liquids,     sampling     7 

London     purple     633 

analysis     634-638 

discussion   of   methods  of  analysis 637 

Longbeinit     553 

Lorenz,    method    of    preventing    contamination    with    magnesia 65 

Lunge,    modification    of    technical    methods 560-562 

Lunge's    nitrometer     415 

improved    apparatus     416 

M 

Magnesia,    estimation    in    ash 611,  614 

mixture     101 

preparation      57 

occurrence    in    phosphates 280 


670  INDEX 

Magnesium    chlorid,    estimation 557 

citrate     solution      jj6 

determination     619 

nitrate     solution,     preparation      58 

pyrophosphate,    color    86,    87 

elimination   of  color    87 

sulfate,    estimation    in    kieserit    559 

Magnetic    deflection    of    flame    320 

Manganese,   determination    619 

in   ash 611,  614 

Manure,    definition    I 

Marls     594 

Mason   method   for   nitrous   acid 472 

Mercury     vacuum     pump      327,  328 

Metallic    platinum,    weighing    in    analysis    569 

Metaphenylenediamin    method    467 

Microscope,  use   in   detecting  adulterant   of  basic   slags 221 

Mineral   phosphates,   determination   of  soluble   and   insoluble  matter 226 

estimation    in    lime    228 

French    Official    methods    248 

method  of  Lasne    249,  250,  251 

occurrence     25 

silica  and  insoluble  bodies 227 

Minerals,    grinding    13 

sampling    12 

Mixed   fertilizers,    sampling ^ 13,    14 

Molybdate    and    citrate    methods     102,  103 

method,    avoidance    of   errors So 

correction   for    errors    80 

error  due  to   arsenic 79 

magnesia     79 

silica     78 

volatility     79 

sources  of  error   78,  79,  80 

solution,    preparation    57 

Molasses,     sugar-beet     533 

Monnier   and  Auriol,   sodium-amalgam   process 441 

Monocalcium     phosphates,     composition     24 

drying     24 

formulae  for   drying   25 

Movement,    influence    on    solubility    of    phosphoric    acid 115 

Muck      594 

N 

Naphthylamin    method     468 

Natural   phosphates,   general   analysis   224 

water  and  organic   matters    224 

Nessler    process     480-484 

reagent     481 

preparation      481-484 

Nesslerizing     434 

Nitrate,    deposits    293 

antiquity      294 

origin     295 

of  lime,  electric  manufacture 315,  316,  317 

soda,   consumption    294 


INDEX  671 

N  itrates,      extraction    434 

qualitative    tests    434 

reduction  by  nascent  hydrogen    435 

statistics   of   production   in    Chili    294 

Nitric   acid,   absorption   in   electric  manufacture 318 

concentration    in    electric   manufacture 319 

cost   of   electric    manufacture 314 

determination     - 391 

ammonia     method     433 

ammonium   picrate   method    464 

colorimetric    method     455 

Crum-Frankland     method 413 

modified    by    Noyes....       414 

de   Koninck's  modification    409-41 1 

Devarda's    method    438 

ferrous  chlorid  process    413 

French    commission    method 393-396 

French    sugar   chemists   method 396 

Gantter    method     421-424 

Gooch    and    G-ruener's   method    453,   454 

Halle    zinc-iron    method     435 

Hooker's  method 456,  457,  458,  459,  460,  461 

in   presence  of  nitrous  acid   465-467 

Kruger's    method    446 

Lunge's   improved   method    416-421 

mercury-sulfuric    acid    method    413 

Mockern    station    method 435 

phenyl-sulfuric    acid   method    461,    462,    463,    464 

Schloesing    modification     392 

Schloesing- Wagner  method    396 

Schmidt's     process     411-413 

Schmitt    method    443 

Schultze-Tiemann     method 403-407 

Sievert    method    440 

Spiegel's    modification    407-409 

Stoklasa    method    439 

Ulsch   method    444 

utility   of   Lunge's   improved  method 421 

Warington's    method    399-403 

Williams- Warington    method     447 

iodometric   estimation    450,   451,   452,   453 

manufacture  in  Norway   314 

production   by   electric    action    313-318 

in   the  United  States 320,   321 

reduction    by    electricity    447 

sodium-amalgam     process     441 

sodium-mercury    amalgam    434 

in  an  acid  solution   441 

to    ammonia    433 

relation    to    organic    colors     425 

retention   by   living  organisms    298 

Nitric    oxid,    measurement 403 

Nitrites,   influence   on   Hooker's  method    460 

Nitrogen,   accumulation 304,   305 

analysis,    official    method     323 

and  phosphoric   acid,    determination   in  the  same  solution 87,   83 


672  INDEX 

Nitrogen,    as    ammonia    383 

deposits  in   soils    292 

determination,   classification   of  methods    321,    322 

French   commission    method    389 

Kjeldahl  method    347-355 

moist  combustion  process,  historical    346 

of  definite  forms    382 

state    of    combination 322 

official    volumetric     323-33 1 

volumetric    method    421-423 

calculation      331 

of   Bureau   of   Chemistry 329,    330 

Johnson    and    Jenkins 331 

from    birds     291 

kinds   in    fertilizers    288 

percentage  in   Chili   saltpeter    299 

seeds  and  seed  residues   288 

states  of    287 

utilization  by  other  than  leguminous  plants 303,   304 

of    atmospheric     301 

waste     292 

Nitrogenous  materials,   microscopic   examination    323 

Nitrous   acid   determination,    Chabrier   method 474-477 

colorimetric    method     467-477 

ferrous   sulfate   method    477 

general    observations    479 

indigo  method   426 

Lunge's    variation    47  3 

volumetric   method    477,   478,   479 

with   starch    as   indicator 474 

Norwegian   nitrate    309 

O 

Official   methods,    solution    of    phosphates 54 

Organic    materials,    sampling 15 

matter,    destruction    51 

by    ignition     ,. 538 

moist  combustion    539 

nitric   and   sulfuric   acids 51,    52 

precipitation    of    phosphoric    acid    therein 65 

nitrogen    determination     389 

Oxidation    towers     314 

Oxidized    nitrogen    determination,    method    of    Schloesing 391 

occurrence     391 

P 

Paris  green    627 

analysis 627-632 

discussion  of  methods  of  analysis    632,  633 

Patrick's    distilling    flask    368 

Peat     594 

Pellet,    method    of   rendering   silica  insoluble    63 

Peraldehyde     651 

Perchlorate,    estimation    in    Chilisaltpeter    390 

method    of    Blattner-Brasseur 391 


INDEX  673. 

Perchloric    acid,    composition    585 

keeping   properties    585 

method     544 

accuracy    587-593 

applicability     59 1 

application   to  crude   potash   salts 589 

general    principles    578 

results     593 

influence   of   carbonates    590,  591 

sulfuric   and   phosphoric   acid 587 

technique      586 

preparation,  method  of  Caspari    580 

Krieder     582-585 

properties      585 

Phosphate,   analysis   of   mineral 49 

breccia     35 

conglomerate      34 

determination,    factors    for    calculation 59 

industry,     control     43 

statistics     43 

lamellar     35 

rocks,  loss  on  ignition    222 

shaly     34 

Phosphates,    analytical    processes     49 

availability   of   raw    285 

composition  of  Tennessee   white    35 

constituents   determined    49 

Dall's   theory  of  origin    31 

drying    mono-calcium    24 

Eldridge's  theory  of  origin    29,   30,   31 

Florida,    origin    26 

general  conclusions    46 

magnitude    of    product     42 

marketed    production     44 

methods   of   solutions    54 

occurrence   in    Canada    '. 42 

the  United    States    4* 

of  black   33 

mineral      25 

origin     27,  28 

Pratt's   theory  of   origin    28 

production    in    the    United    States    43.  44 

properties     39,  40 

reactions    of    precipitation     58 

solution     58 

Shaler's  theory  of   origin    31 

South    Carolina    deposits    41 

statistics    and    composition    40 

value  of   fine   ground    5 

product    42,   43 

white,    occurrence    of ., 34 

world's   production    45,   46 

Wyatt's     theory    of     origin     27,  28 

Phosphatic    fertilizers,     availability     120 

French    official   classification    72 

slag,  detection  of  adulteration    219 

estimation   of  total   phosphoric    acid 198 

22 


674  INDEX 

Phosphatic  slag,  estimation  of  total  phosphoric  acid,   alternate  method 198 

German  manufacturer's  method  of  analysis 217 

relative   availability    197 

sifting     197 

solubility     196 

solution     197 

1  'hosphomolybdate,    direct    weighing     122 

precipitate,    direct    weighing,    Berju's    method 125 

Cladding's   modification    130 

method  of    Graftiau 127,   128 

Hanamann      ....        122 
Hundeshagen       123-126 

Lorenz     123 

Pellet     129 

Sherman  and  Hyde  125 

Woy     124 

Neumann's   method    125 

Phosphoric    acid    absorption     284 

amount  removed  by  crops 46 

and  nitrogen,   determination   in  the  same  solution 87,  88 

citrate-soluble     185,    186 

comparison   of   different   methods   of  estimation 212 

conduct  of  the  volumetric  method 160 

determination     620 

Albert    method    180 

ammonio-manganous    method    15 ' 

Brussels    Congress    method 99.    100 

citrate  method    88,    89,   90,    182 

for  small   amounts 105 

French    official    method 72.    73 

general    method    55 

German    experiment  station  method 68 

fertilizer   Association   method 246 

in    all    phosphates 184 

ash    614,   615 

basic    slags     184 

by    the    Halle    station    methods       199 

by    Wagner's    method 201 

direct  and  molybdate  method..       213 
precipitation       method 

comments    208 

excess  of  iron   167 

slags     214 

superphosphates     186 

influence  of  aluminum 83,  84,  85,  86 

calcium  and  magnesium..   83-86 

calcium    83,    84,    85,    86 

magnesium    83,   84,    85,    86 

silica    60 

tartaric  acid   . 60 

international  method    66 

International  Steel  Standard  Committee  method       173 

Jensch    method    220 

molybdate  method    181 

molybdic   method  of  the  German   experiment 

stations    70,    71 

Norwegian    method    68,    69,    70 


INDEX  675 

1'hosphoric  acid   determination  of  amounts  soluble  in  citric   acid  solution 215 

citrate-soluble   in    basic   slag 200 

citric-acid-soluble   in  basic    slag    218 

official    Swedish   method 74.   75.    7^ 

Oliveri    method 184 

preferred    method     5<> 

preparation  of  reagents 56,  57,   58 

royal  experiment  station  of  Holland  method  76,  77,  78 

silver   method    177 

technical      1 79 

total     187 

Veitch    method   for   available    120 

modification    of    Ross    method 64-65 

volumetric  method   13° 

in    superphosphates     147 

investigation  by  official  chem- 
ists             1 58 

optional     159 

direct   determination    of   available    63 

precipitation  of  citrate-soluble 106,   107 

estimation  as  lead  compound   160 

fixation    in    soils    283 

loss    by    incineration    S2»    53 

precipitate,  time  of  subsidence    137 

precipitation    by    magnesium   citrate    135 

filtration  and  washing 137 

with  metallic  tin 108,    109 

removal    by   iron    chloric!    613 

solubility   in   ammonium   citrate no 

soluble,   molybdic  method  of  the   German   experiment   stations         72 

solution,   verification  of  standard 140 

solvent   for  mineral   phosphates    282 

time   required   for   precipitation    62 

titration    in    steel    174 

of   the    yellow    precipitate    153,    154 

calculation    of    results....        156 
comparison    of     results...        157 

reagents     155 

typical    solution     139 

water-soluble     166-186 

German  method  of  determination    68 

Phosphorus,     calculation  in  iron   and  steel    172 

in  steel    176,    177 

content    in    pig    iron 194 

Platinic   chlorid,    preparation    559 

Platinum    method^   sources    of    error    570 

waste,    recovery    573,    574 

weighing,     metallic     569 

Polyhalit      486 

description      498 

Potash,    actual    491 

analysis,  effect  of  concentration  on   accuracy    571 

preparation    of    sample     538 


676  INDEX 

Potash  analysis,  technical  methods     560 

availability    in    ashes     533 

barium     oxalate     method     562 

calcium    chlorid     method     564 

consumption    for   agricultural  purposes    504 

in    different    states     505 

deposits    486-490 

Dutch    method     548 

estimation    as    perchlorate     578-593 

factors 572,  573 

in     guanos     547 

presence  of  sulfates  of  the  alkalies 566,  567 

extraction   from   ground  rock    524,  525 

factors       572 

for    conversion    •  543 

forms  in   fertilizers    536,  537 

German  potash  syndicate  methods    55° 

in    factory    residues     5°- 

sugar-beet  molasses    533 

insoluble  in  plants   535,  536 

kinds    in   beet   molasses    534 

method   of    German    fertilizer    union    546 

methods    used    at    the    Halle    station    546,  547 

mining     489 

Moore's    method       564-507 

occurrence     486 

official   agricultural   method     » 54* >  542 

French  commission   methods    543,  544 

optional    method    542,  543 

organic     sources     526 

percentage    in    fertilizers    566 

perchloric    acid    method    544 

platinic     chlorid     method     540 

price   per   unit  in    feldspar    523 

production    of    crude    salts    5°2,  5°3 

salts,    application    of    theory    of    deposition 517 

changes    in    situ    5<><> 

effect   of   temperature  on   deposition    51° 

graphic   representation  of   deposition    S'^'SM 

law   of  crystallization    511 

manufacture    490,  491 

methods  of  analysis  for  concentrated 555,  556 

production  of  concentrated    503 

rapid    methods    568 

sequence   of  deposition    515,  516 

theory    of    deposition 506 

van't  Hoff's  theory  of  deposition   508-518 

source   of,   in   soils    * 485 

Swedish    methods     549 

qualitative    detection     539,  540 

quantity    removed   by   crops    537 

Potassium    cyanid     648 

cyanogen    determination    648 

hydroxid   solution,    tension    337 

in    plants,     determination     620 

Potassium-magnesium    carbonate,    commercial    503 


INDEX  677 

Potassium    permanganate    solution,    standardization 174 

Potassium-platino-chlorid,     differences     in    crystals     573 

Potassium    sulfate,    commercial    501 

Protein,   separation    from   amid  and  other   forms  of   nitrogen 387 

Pure    water,    preparation     484 

Pyrophosphate,    examination    for    impurities    62 

R 

Rain    water,    collection    of    samples     479 

nitrogen     in     448 

preparation   of    samples    480 

Reductor,    Jones    169,    170,  171' 

manipulation     175 

Reitmair,   value   of   finely   ground   bone    47,   48,    49 

Reversion  of  phosphoric  acid,  theory    112,   113 

Reverted    phosphates,    solution    with    ammonium    citrate     149,  150 

phosphoric     acid,     arbitrary    determination     112,  113 

definition      113 

determination     147 

Road     materials,     sampling     16 

Rodonda   phosphate    .' 220 

Ross,    determination    of    reverted    phosphoric    acid 63 

Rossler    ignition    furnace    97 

Ruffle     method,   Boyer's   modification    345 

observations     344 

official      343 

S 

Salicylic    acid    method    377 

theory 379 

Salt,   agricultural    uses    6oa 

hydroscopic    character     603 

value    603 

Sample,    extraction   with   distilled   water    148 

preparation     for     analysis     148 

in    laboratory    19 

Samples,    French   agricultural  method  of  preparation 20 

German    method   of    preparation    21 

influence    of    state    of    subdivision     19 

international   method   of   preparation    20 

methods  of  drying  22 

preservation      9 

special    cases    22 

subdivision      9 

Sampling     i 

barnyard    manures     16 

general    principles    • 5 

international    methods     18 

method  of  French  experiment  station    17 

sugar   chemists    17 

methods     8 

minerals     13 

object   6 

official    methods    17 

organic    materials     15 

road    materials    1 6 


678  INDEX 

Sand,     determination     637 

estimation    in   ash    610,    613,  618 

Schmitt,     nitric     acid     method     443 

Schonit 500,  50 1 

Sea   weeds    289 

value   as  fertilizer    290 

Shaler,    origin   of  phosphates    31 

Sievert,    nitric   acid   method    440 

Silica    and    fluorin,    loss    in    analysts 227 

estimation  in   ash 610,    613,  618 

influence    on    phosphoric    acid    determination     60 

insolubility    6^ 

Silicic  acid,  separation   in   the  estimation  of  phosphoric  acid 211 

Silver   method   for   phosphoric   acid    177 

volumetric     178 

Slag    phosphates,    determination    of    phosphoric    acid     67 

Soaps     640 

analysis    640,  641 

determination  of   total   alkali    641 

Soda   and   potash,    analysis   of  caustic    641-643 

caustic      641 

lime,    hydrogen   method    341 

process    338-342 

coloration    of   product 342 

general    considerations    343 

official   French    method 341 

official    method    339,  340 

Ruffle    method     343 

saltpeter   293 

Sodium    acetate    solution     138 

amalgam,     preparation     442 

chlorid,    estimation     556 

nitrate     functions     297 

dissociation     298 

Soils,    impregnated   with   nitrogen    29^ 

Solids,    sampling     8 

Solubility,    test    for    adulteration    of    basic    slag    223 

Specific    gravity,    test    for    adulteration    of    slags    224 

Stall     manure     594 

effect  on  texture  of  soil 604,  605 

properties  and  uses   6°4 

Stassf  urt,     deposits      488 

potash   deposits    486,  488 

Stirrer,     Huston's     mechanical     118 

Stoklasa,  determination  of  nitric  acid    439 

Subterranean     insects     648 

Sucking    insect,    external     640 

Sulfanilic    acid    method     468 

Sulfids,    occurrence    in    basic    slags    222 

Sulfur   in   plants,   determination    620 

Sulfuric   acid,  determination    260,    557,  620 

estimation   in    ash    614 

quantity  required  in  superphosphate  manufacture 280,   28:,  282 

removal  in  perchloric  acid  method 588 


INDEX  679 

Superphosphates,   chemistry   of  manufacture 277 

prepared   with    phosphoric    acid    282 

Swedish     citrate     method     98,  99 

Sylvin,    description    499 

Sylvinit,    composition    494 

description     499,  500 

method    of    analysis 550 


Tankage     290 

Tartaric    acid,    influence    on   phosphoric    acid    estimation 60 

prevention    of    iron    precipitation 65 

Temperature    affecting    deposition    of    potash    salts S'° 

influence    on    citrate    solubility    •  1 1 1 

digestion   of   phosphoric  acid    202 

Tennessee  phosphates,   analyses    35 

character    and    origin    32 

classification     32,  33 

composition     41 

statistics      40 

Tetracalcium    phosphate,    molecular    structure     195 

Thiocyanates,   determination    385,  386 

Thomas    meal    203 

slag     192 

Tin,    phosphoric    acid    precipitate     108,  109 

Tobacco  and   tobacco   extract    646 

nicotine    determination    647 

stems     526 

composition     527 

waste     526 

Total    phosphoric    acid    determination    147 

official    method    59 

U 

Ulsch    method,    theory     445 

applied   to   mixed    fertilizers 445 

nitric  acid  method   444 

Uranium   method    for   phosphoric    acid    132 

in    absence   of   iron    183 

presence    of    iron    1 83 

preparation   of  sample    132,  133 

nitrate    solution     1 38 

solution,     conduct     of     titration     i4S»  146 

correction    of   titration    142 

errors  attending  use    143,  144 

standardization      140,  181 

titration     141 

volumetric   process,   general   conclusions    151 

V 

Vanadium,   estimation    274,    273,  276 

method  of  Rosenheim  and  Holverscheit    276 


68O  INDEX 

Volumetric  determination  of  phosphoric  acid,  classification  of  methods    130- 

method,   calculating   results 337 

disuse     337 

use    for    nitrogen    determination    337 

processes,    direct   titration    131 

for  phosphoric  acid  titration   after  previous  separation 131 

silver   method    17% 

solution      134 

W 

Wagner's    digestion    apparatus    for    basic    slags 202 

method   for   basic   slags,    solutions   employed    203 

phosphoric  acid  and  basic  slags 20: 

Water-   and   citrate-soluble   phosphoric    acid   precipitation    119 

Water,    preparation    of    ammonia   free    481,  482 

Water-  soluble  arsenic   oxid    636 

arsenic    oxid    determination    639 

arsenious   oxid    636 

determination 629,  630 

phosphoric   acid,   official  method    60 

volumetric   method    160 

Waste    leather    608 

matters     as     fertilizers     2 

White  phosphates,  Hayes"  theory  of  origin 36,  37,  38 

occurrence      34 

origin   36 

properties     39 

specific   gravity    39 

utilization     39 

Williams-Warington  method  for  nitric  acid  determination   447 

Wood    ashes    594 

analysis     609 

composition     529 

Y 

Yellow    precipitate,    percentage   of    phosphoric    acid    164 

titrating     164 

weighing     , 164 

Z 

Zinc  sulfid  and  sodium  thiosulfate   method    377 


UNIVERSITY  OF  CALIFORNIA  AT  LOS  ANGELES 

THE  UNIVERSITY  LIBRARY 
This  book  is  DUE  on  the  last  date  stamped  below 


Form  L-9-20m-8,'37 


s 

587 

W6UP 

1906 

v.2 


